2.2* Flashcards
(318 cards)
1
Q
What is a hydrogen bond?
A
A weak interaction that can occur whenever molecules contain a slightly negatively charged atom bonded to a slightly positively charged hydrogen atom.
2
Q
What is a hydrolysis reaction?
A
A reaction that occurs when a molecule is split into two smaller molecules with the addition of water.
3
Q
What is a monomer?
A
A small molecule which binds to many other identical molecules to form a polymer.
4
Q
What is a polymer?
A
A large molecule made from many smaller molecules called monomers.
5
Q
What do atoms consist of?
A
A nucleus ( protons and neutrons ) surrounded by shells of electrons.
6
Q
When are its atoms stable?
A
When their outermost shell is full.
7
Q
Describe covalent bonding.
A
Atoms of different elements have different amount of atoms in their outermost shells. For example, carbon has four electrons. By sharing electrons with other atoms, the atom’s outermost shell can be ‘filled’ and it becomes strongly bonded with the other atom.
8
Q
What is a condensation reaction?
A
Reaction that occurs when two molecules are joined together with the removal of water.
9
Q
How is a covalent bond drawn?
A
By a single line (the equivalent of sharing one electron)
10
Q
Explain the covalent bonding of methane.
A
Because carbons outer shell is filled by four electrons, carbon forms four covalent bonds.
11
Q
How many covalent bonds do oxygen, hydrogen and nitrogen form?
A
Hydrogen forms a single covalent bonds, oxygen two covalent bonds and nitrogen three covalent bonds.
12
Q
Describe the carbon-hydrogen bond.
A
The carbon-hydrogen bond is one of the most important in organic molecules . Hydrogen has one electron. Carbon can therefore bind with four hydrogen atoms. The carbon-carbon bond is also very important in hydrocarbon chains. Sometimes a double bond can form (the equivalent of sharing two electrons).
13
Q
Explain the condensation which happens on your windows on a cold day.
A
When condensation happens on your windows on a cold day, water vapour in the air has changed state and settled on a window as liquid. The water vapour has been removed from the air.
14
Q
When does a condensation reaction occur? And what can this allow?
A
A condensation reaction occurs when two molecules are joined together with the removal of water. In the same way, two molecules can be split apart with the addition of water.
15
Q
What is a hydrolysis reaction?
A
When water is split by a condensation reaction.
16
Q
When do almost all condensation reactions happen?
A
Almost all condensation reactions happen in the same way, when two OH- groups react together. The reaction involves the breaking and formation of covalent bonds.
17
Q
Describe what is added in hydrolysis and taken away in condensation reactions.
A
H2O is added in hydrolysis and a covalent bond is broken. H2O is removed in condensation. A new covalent bond is formed. In both hydrolysis and condensation reactions the OH groups of molecule 1 and molecule 2 are close to each other.
18
Q
Name the type of molecule, monomer, and polymer that contain C, H and O.
A
Molecule; Carbohydrate Monomer; Monosaccharides - e.g. glucose Polymer; Polysaccharides e.g. Starch
19
Q
What is responsible for linking and splitting apart biological molecules in living things.
A
Condensation and hydrolysis reactions.
20
Q
The units which are linked together in condensation reactions are called what?
A
Monomers
21
Q
What happens when two monomers join together?
A
They form a dimer.
22
Q
What happens when lots of monomers join together?
A
They form a polymer.
23
Q
Name the type of molecule, monomer, and polymer that contain C, H, O, N, S
A
Molecule; Protein Monomer; Amino acids Polymer; polypeptides and proteins.
24
Q
Name the type of molecule, monomer, and polymer that contain C, H, O, N, P
A
Molecule; Nucleic acid Monomer; Nucleotides Polymer; DNA and RNA
25
How much of the human body do hydrogen and carbon make up?
Hydrogen atoms make up 60% of the atoms in the human body. Carbon atoms make up 11% of the atoms in the human body.
26
What does does water consist of?
Two hydrogen atoms, each covalently bonded to one oxygen atom.
27
Why is water polar?
Because the oxygen atom has a greater number of positive protons in its nucleus, this exerts a stronger attraction for the shared electrons. This means the oxygen atom becomes slightly negative, and the hydrogen atoms become slightly positive. When this happens, we say the molecule is polar.
28
On a water molecule are the hydrogen positive or negative?
Positive end (poles) of molecule.
29
On a water molecule are the oxygen positive or negative?
negative end (pole) of molecule.
30
What is a hydrogen bond?
A weak interaction which happens wherever molecules contain a slightly negatively charged atom bonded to a slightly positively charged hydrogen atom.
31
What is the strength of a hydrogen bond compared to a covalent bond?
The bond is weaker than a covalent bond.
32
Where do thousands of hydrogen bonds stabilise a molecule?
In some polymers, thousands and thousands of hydrogen bonds form between chains of monomers. Having many bonds like this helps stabilise the structure of some biological molecules.
33
Water has a number of properties that are essential for life, many of which depends on what?
The polar nature of the water molecules and on hydrogen bonding between water molecules.
34
What do water molecules do unlike other liquids.
As in any liquid, water molecules constantly move around. Unlike other liquids, as they move they continually make and break hydrogen bonds.
35
Why is water a liquid at room temperature?
The hydrogen bonds between water molecules make it more difficult for them to escape as a gas. By contrast, other less polar, but similarly sized molecules (e.g. H2S) are gasses at room temperature. Even with hydrogen bonds, water has quite a low viscosity, which means it can flow easily.
36
What can water do because it is a liquid at room temperature? (4 things)
Provide habitats for living things in rivers, lakes and seas. Form a major component of the tissues in living organisms. Provide a reaction medium for chemical reactions. Provide an effective transport medium, e.g. in blood and vascular tissue.
37
What does the density of water provide?
The density of water provides an ideal habitat for living things. If water was less dense, aquatic organisms would find it very difficult to float.
38
What happens when most liquids get colder and what would happen if this was the case with water?
When most liquids get colder, they become more dense. if this was the case with water at the top of the pond would freeze and sink. The water replacing it at the top of a pond would freeze and sink. The water replacing it at the top would do the same, until the pond was full of ice
39
How does water behave when it freezes?
But ice behaves differently. It becomes more dense as it gets colder until about 4 degrees. As it goes from 4 degrees to freezing point, because of its polar nature, the water molecules align themselves in a structure which is less dense than liquid water.
40
What happens because ice is less dense than water?
Aquatic organisms have a stable environment in which to live through the winter. Ponds and other bodies of water are insulated against extreme cold. The layer of ice reduces the rate of heat loss from the rest of the pond.
41
What is water a good solvent for?
Water is a good solvent for many substances found in living things. This includes ionic solutes such as sodium chloride and covalent solutes such as glucose.
42
Why is water a good solvent?
Because water is polar, the positive and negative parts of the water molecules are attracted to the negative and positive parts of the solute.The water molecules cluster around these charged parts of the solute molecules or ions, and will help to separate them and keep them apart. At this point they dissolve and a solution is formed.
43
What can take place because water is a good solvent?
Molecules and ions can move around and react together in water. Many such reactions happen in the cytoplasm of cells which is over 70% water. Molecules and ions can be transported around living things whilst dissolve in water.
44
How does a drop of water demonstrate cohesion?
A drop of water on a flat surface does not spread out, but can look almost spherical. This is because hydrogen bonding between the molecules pulls them together. The water molecules demonstrate cohesion.
45
How does cohesion happen at the surface of water as well?
The water molecules at the surface are all hydrogen-bonded to the molecules beneath them, and hence more attracted to the water molecules beneath than to the air molecules above. This means the water contracts (because the molecules are being pulled inwards), and it gives the surface of the water an ability to resist force applied to it. This is known as surface tension.
46
What can happen because of cohesion and surface tension.
Columns of water in the plant vascular tissue are pulled up the xylem tissue together from the roots. Insects like pond skaters can walk on water.
47
What is water temperature a measure of?
The kinetic energy of the water molecules.
48
How are water molecules held together, and what does this mean for heating it up?
Water molecules are held together quite tightly by hydrogen bonds. Therefore, you have to put in a lot of heat energy to increase their kinetic energy and temperature.
49
What is the amount of heat energy required to raise the temperature of water known as?
The amount of heat energy required is known as specific heat capacity (4.2 KJ of energy to raise the temperature of 1 kg of water by 1 degree)
50
What does the specific heat capacity of water mean for living things?
Because the main component of many living things is water, and many organisms live in water, its high specific heat capacity is important; Living things, including prokaryotes and eukaryotes, need a stable temperature for enzyme controlled reactions to happen properly. Aquatic organisms need a stable environment in which to live.
51
What is the latent heat of vapourisation?
When water evaporates, heat energy known as the latent heat of vapourisation, helps the molecules to break away from each other to become a gas.
52
Why has water got a high latent heat of vapourisation?
Because the small molecules are held together by hydrogen bonds, a relatively large amount of energy is needed for water molecules to evaporate.
53
What does the high latent heat capacity of vapourisation of water mean for living things?
Water can help to cool living things and keep their temperature stable. For example, mammals are cooled when sweat evaporates, and plants are cooled when water evaporates from mesophyll cells.
54
What is water a reactant in?
Water is also a reactant in reactions such as photosynthesis, and in hydrolysis reactions such as digestion of starch, proteins and lipids.
55
Describe waters properties as a reactant.
Its properties do not directly draw on its polarity, but its role as a reactant is extremely important for digestion and synthesis of large biological molecules.
56
What is an amino acid?
Monomers of all proteins, and all amino acids have the same basic structure.
57
What is a peptide bond?
A bond formed when two amino acids are joined by a condensation reaction.
58
What do proteins comprise of?
Proteins are large polymers comprised of long chains of amino acids.
59
The properties of proteins give them a variety of functions. Describe three functions of proteins.
They form structural components of animals in particular. For example, muscles are made of protein. Their tendency to adopt specific shapes make proteins important as enzymes, antibodies and some hormones. Membranes have protein constituents that act as carriers and pores for active transport across the membrane and facilitated diffusion.
60
What do both plants and animals need to make proteins?
Both plants and animals need amino acids to make proteins. Animals can make some amino acids, but must ingest the others (called essential amino acids). Plants can make all the amino acids they need, but only if they can access fixed nitrogen (such as nitrate).
61
What elements are in each amino acid?
Each amino acid contains the elements carbon, hydrogen, oxygen and nitrogen. Some amino acids contain sulphur.
62
How does the amount of amino acids compare to the amount found in proteins?
There are over 500 different amino acids, but only 20 of them are proteinogenic, which means they are found in proteins.
63
What does each protein chain of amino acids have at each end?
An amino group (-NH2) at one end, and a carboxyl (-COOH) group at the other end. Molecular structure of an amino acid is on pg. 65
64
On a molecular structure of an amino acid what does the R group stand for?
It does not stand for a particular element, but is different in each amino acid. In glycine, it is simply an H atom.
65
Give an example of where the R group can be a lot more complicated.
In alanine it is CH3 whereas in cysteine it is CH3S.
66
What does the name of almost all amino acids end in? And what are the exceptions.
-ine. The only exceptions are those which have an acidic R group, such as aspartic acid and glutamic acid.
67
What do the R groups in amino acids vary in?
By size, by charge and by polarity, with some being hydrophobic and some being hydrophilic.
68
What's the simplest amino acid?
Glycine
69
When cab amino acid can act as buffers?
When in dissolved water.
70
Amino acids can act as buffers; What happens when amino acids are dissolved in water?
When dissolved in water, the amino group and carboxyl group can ionise. This means that the amino group can accept an H+ ion to change from NH2 to NH3+. The carboxyl group can give up an H+ ion to change from COOH to COO-.
71
Amino acids can act as buffers; What are the symbol equations for the carboxyl and amino groups accepting or giving up H+ ions to change form.
-COOH ~ –COO- + H+ The carboxyl group acts as an acid, in producing H+ ions. -NH2 + H+ ~ -NH3+ The amino group acts as a base, in accepting H+ ions:
72
Amino acids can act as buffers; How will this change with the pH.
At a low pH (where there are lots of H+ ions in a solution), the amino acids will accept H+ ions. At high pH (where there are fewer H+ ions in solution), the amino acid will release H+ ions.
73
Amino acids can act as buffers; What does the amino acids reaction to acids and alkalis tell you about its properties.
This means an amino acid has acidic and basic properties, and so is known as amphoteric. In a long chain of amino acids, you will find amino acids, you will find amino and carboxyl groups on each end, but there are also may on the R-groups of different amino acids.
74
Explain what buffering is?
Protein chains can be affected by this amphoteric nature. By accepting and releasing H+ ions, amino acids can help regulate changes in PH. This is known as buffering. A buffer is a substance which helps to resist large changes in PH.
75
How are amino acids joined together?
Amino acids are joined together by by covalent bonds called peptide bonds.
76
What does making a peptide bond involve?
Just like the glycosidic bond and the ester bond, making a peptide bond involves a condensation reaction, and breaking a peptide bond involves hydrolysis.
77
What breaks down peptide bonds in the body.
Enzymes catalyse these reactions. Protease enzymes in the intestines break down peptide bonds during digestion. They also break down hormones so that their effect is not permanent.
78
As more amino acids join together, how do their names change?
All amino acids are joined together in a similar way, whatever R groups they may have. Two amino acids joined together are known as a dipeptide. Joining a longer chain of amino acids together forms a polypeptide. A protien may consist of a single polypeptide chain, or more than one chain bonded together.
79
How do two amino acids join to form a dipeptide molecule?
amino acid + amino acid = dipeptide molecule + water. It is a condensation reaction, a peptide bond (covalent) is formed and water is used up. The of part of the carboxyl group is released along with a hydrogen from the amino group to form water. The carbon from the carboxyl group then joins to the nitrogen form the amino group.
80
How does a dipeptide molecule form amino acids?
Dipeptide molecule + water = amino acid + amino acid. This is a hydrolysis reaction, a peptide bond (covalent) is broken and water is used up. The carbon from the carboxyl group and the nitrogen form the amino group split, and a hydrogen bonds with the nitrogen and a hydroxide bonds with the carbon.
81
What makes a polypeptide chain relatively stiff and rigid?
The peptide bond is depicted as a single bond, but due to the electron arrangement around the bond, it has some of the properties of a double bond. This means that the bond is shorter than a conventional C-N bond. It also inhibits rotation around the peptide bond. This makes the polypeptide chain relatively stiff.
82
What is a primary structure?
The sequence of amino acids found in a molecule.
83
What is a secondary structure?
The coiling or folding of an amino acid chain, which arises often as a result of hydrogen bond formation between different parts of the the chain. The main forms of secondary structure are the helix and the pleated sheet.
84
What is a quaternary structure?
Protein structure where a protien consists of more than one polypeptide chain.
85
What is a tertiary structure?
The overall three-dimensional shape of a protien molecule. Its shape arises due to interactions including hydrogen bonding, disulphide bridges, ionic bonds and hydrophobic interactions.
86
Why is the number and order of amino acids in a protien chain important?
Changing just one amino acid can alter the function of the protien.
87
How many possible ways are there of ordering amino acids are there and why?
Because there are 20 amino acids, at every point in the chain there are 20 alternatives. Given that most proteins are at least 100 amino acids long, this gives an enormous number of different proteins that could be formed. There are 20 x 100 possible ways of ordering 100 amino acids.
88
What determines a proteins, function and shape.
The function of a protien is determined by its structure. The order of amino acids in the primary structure will determine the shape of the protien molecule, through its secondary, tertiary and quaternary structure.
89
Protein structure and bonding; How is a helix created?
The chain of amino acids is not straight, but twists into a shape called the secondary structure. Some chains coil into a alpha helix, with 36 amino acids per 10 turns of the helix.
90
Protein structure and bonding; How is a helix held together?
The helix is held together by hydrogen bonds between the -NH group of one amino acids and the -CO group of another four places ahead of it in the chain.
91
Protein structure and bonding; How is a zig-zag structure created?
Other chains fold very lightly in a zig-zag structure. When one such chain folds over on itself, this produces a Beta-pleated sheet.
92
Protein structure and bonding; How is a zig-zag structure held together?
Hydrogen bonds between the -NH group of one amino acid and the -CO group of another further down the strand hold the sheet together.
93
What makes the beta-pleated sheet stable structures at optimal temperature and PH.
Although hydrogen bonds are relatively weak, many are formed, which makes both the alpha-helix and the beta-pleated sheet stable structures at optimal temperature and PH.
94
How do secondary structures vary, do they all have a regular patten?
Some chains do not adopt any regular structure, and some chains may have more than one secondary structure at different ends of the chain.
95
When is a tertiary structure formed?
When these coils and pleats themselves start to fold, along with areas of straight chains of amino acids, this forms the tertiary structure.
96
How is the tertiary structure held together?
The tertiary structure is a very precise shape which is held firmly in place by bonds between amino acids which lie close to each other.
97
What shape may the tertiary structure form?
The tertiary structure may adopt a super-coiled shape (e.g. in fibrous proteins) or a more spherical shape (in globular proteins).
98
What does a quaternary structure describe?
Many proteins are made up of more than one polypeptide chain. The quaternary structure describes how multiple polypeptide chains are arranged to make the complete protien molecule.
99
How may a quaternary structure be held together?
This may also be held together with the same types of bond that hold the tertiary structure together.
100
How is the primary structure of proteins bonded together?
The primary structure of proteins, the chains of amino acids, is held together by peptide bonds which are covalent bonds, hence very strong.
101
How is the secondary, tertiary and quaternary structure of proteins bonded together?
Other types of bond form between amino acids in different parts of the polypeptide chain. The secondary structure is primarily held together by hydrogen bonds, but the tertiary structure and quaternary structure are held together by hydrogen bonds and many others.
102
What do the terms primary, secondary and tertiary structure refer to?
A single polypeptide chain.
103
What does the quaternary structure describe?
The association between two or more polypeptide chains.
104
Hydrogen bonds: How are hydroxyl, carboxyl and amino groups formed?
Like in water, hydrogen bonds from between hydrogen atoms with a slight positive charge and other atoms with a slight negative charge. In amino acids, these form in hydroxyl, carboxyl and amino groups.
105
Give some examples, hydrogen bonds forming in hydroxyl, carboxyl and amino groups.
For example, hydrogen bonds may form between the amino group of one amino acid and the carboxyl group of another. They may also form between polar areas of the R groups on different amino acids.
106
What may hydrogen bonds forming between polar areas of the R groups on different amino acids be particularly involved in?
These in particular are involved in keeping the tertiary and quaternary structure of the protien in the correct shape.
107
What can the presence of multiple hydrogen bonds give?
A lot of strength.
108
What is importance of ionic bonds in a polypeptide chain?
Ionic bonds can form between those carboxyl and amino groups that are part of R groups. These ionise into NH3+ and COO- groups. Positive and negative groups like this are strongly attracted to each other to each other to form an ionic bond.
109
What is the importance of disulphide links in a polypeptide chain?
The R group of the amino acid cysteine contains sulphur. Disulphide bridges are formed between the R groups of two cysteines. These are strong covalent bonds.
110
Where do Hydrophobic and hydrophilic parts of R groups tend to associate in a polypeptide?
Hydrophobic parts of the R groups tend to associate together in the centre of the polypeptide to avoid water. In the same way, hydrophilic parts are found at the edge of the polypeptide to be close to water.
111
What does hydrophobic, hydrophilic interactions cause?
Hydrophobic and hydrophilic interactions cause twisting of the amino acid chain, which changes the shape of the protien. These interactions can be a very important influence, given that most proteins are to be found surrounded by water inside a living organism.
112
What is carbohydrate?
A group of molecules containing C, H and O.
113
What is a glycosidic bond?
A bond formed between two monosaccharides by a hydrolysis reaction.
114
What do carbohydrates contain?
Carbon, hydrogen and oxygen.
115
How are the atoms bonded in carbohydrates?
Carbohydrates are hydrated carbon which means that for every carbon there are two hydrogen atoms and one oxygen atom.
116
What are functions of carbohydrate?
The functions of carbohydrates are three-fold. They act as a source of energy (e.g. glucose), as a store of energy (e.g. starch and glycogen) and as structural units. (e.g. cellulose in plants and chitin in insects). Some carbohydrates are also part of other molecules, such as nucleic acids and glycolipids.
117
What are the three main groups of carbohydrates?
There are three main groups of carbohydrates: monosaccharides, disaccharides ad polysaccharides. The common monosaccharides and disaccharides all have names ending in -ose.
118
Why are monosaccharides important?
Monosaccharides are the simplest carbohydrates. They are particularly important in living things as a source of energy.
119
What are monosaccharides?
They are sugars, which taste sweet, are soluble in water and are insoluble in non-polar solvents.
120
Why are monosaccharides suited to their role?
They are well suited to this role because of the large number of carbon-hydrogen bonds.
121
What is arrangement of atoms in a monosaccharide?
Monosaccharides can exist as straight chains or in a ring or cyclic forms. They have a backbone of single bonded carbon atoms, with one double-bonded to an oxygen atom to form a carbonyl group
122
How do different structures of monosaccharides vary in the amount of carbon atoms?
Hexose sugars have six carbon atoms, pentose sugars have five carbon atoms and triose sugars have three carbon atoms.
123
Why can monosaccharides be monomers?
Monosaccharide hexose sugars, like glucose, are the monomers of more complex carbohydrates, and they bond together to form disaccharides or polysaccharides.
124
Give an example of which monosaccarides exists as straight chains and which can be found in a ring.
In solution, triose and tetrose sugars exists as straight chains. However, pentose and hexoses are more likely to be found in a ring or cyclic form.
125
In both a straight chain and cyclic forms glucose can exists as a number of isomers, how does it form these isomers?
In the straight-chain form, the -H and -OH can be reversed. In a ring shape, isomers can also form. The ring is formed when the oxygen attached to the carbon 5 bonds to carbon 1. Because the -OH and -H on carbon 1 can be above or below the plane of the ring when the ring forms, there are two isomers alpha and beta - glucose. This small difference appears insignificant, but it becomes very important when glucose molecules polymerise into starch or cellulose.
126
Where has the word saccharide been derived from?
The Greek word sakkharon, which means sugar.
127
Give some examples of a disaccharide.
Like monosaccarides, disaccharides are sweet and soluble. The most common disaccharides are maltose (malt sugar), sucrose and lactose (milk sugar).
128
Give an example of a reducing sugar and a non-reducing sugar.
Maltose and lactose are reducing sugars, whereas sucrose is a non-reducing sugar.
129
What are disaccharides made of?
Disaccharides are made when two monosaccharides join together.
130
Give four combinations of when two monosaccarides join together to form a disaccharide.
σ-glucose + σ-glucose = maltose
σ-glucose + fructose = sucrose
ß-galactose + σ-glucose = lactose
ß-glucose + ß-glucose = cellobiose
131
What happens when two monosaccharides join to form a disaccharide?
When they join a condensation reaction occurs to form a glycosidic bond. Two hydroxyl groups line up next to each other, from which a water molecule is removed. This leaves an oxygen atom acting as a link between the two monosaccharide units.
132
How are disaccharides broken down?
Disaccharides are broken into monosaccharides by a hydrolysis reaction, which requires addition of water. The water provides a hydroxyl group (-OH) and a hydrogen (-H), which help the glycosidic bond to break.
133
Give an example of a disaccharide that is broken down by a hydrolysis reaction.
Cellobiose is obtained by the hydrolysis of the polysaccharide cellulose.
134
Give the molecular formula, role in the body and type of sugar for alpha-glucose.
Molecular formula- C6H12O6 Role in the body- Energy source. Component of starch and glycogen, which act as energy stores. Type of sugar- Hexose
135
Give the molecular formula, role in the body and type of sugar for beta glucose.
Molecular formula- C6H12O6 Role in the body-Energy source. Component of cellulose, which provides structural support in plant cell walls. Type of sugar- Hexose
136
Give the molecular formula, role in the body and type of sugar for ribose.
Molecular formula- C5H10O5 Role in the body- Component of ribonucleic acid (RNA), ATP and NAD. Type of sugar- Pentose
137
Give the molecular formula, role in the body and type of sugar for deoxyribose.
Molecular formula- C5H10O4 Role in the body- Component of deoxyribonucleic acid (DNA). Type of sugar- Pentose
138
What changes in the formation and splitting of maltose from alpha-glucose?
The glycosidic bond is formed between carbon 1 of one alpha-glucose molecule and carbon 4 of the other alpha- glucose molecule. It is known as a 1-4 glycosidic bond. Diagram page 55.
139
What happens in the condensation reactions and hydrolysis reactions where glycosidic bonds are formed and hydrolysed?
They are catalysed by enzymes. In a condensation reaction water is eliminated (released) and a glycosidic covalent bond is formed. In a Hydrolysis reaction water is used up and a glycosidic (covalent bond) is broken. Diagram page 55.
140
What are homopolysaccharides?
The polymers of monosaccharides, they are made of hundreds of thousands of monosaccharide monomers bonded together. They are made solely of one kind of monosaccharide called homopolysaccharides
141
What are heteropolysaccharides?
Polysaccharides made of more than one monomer called heteropolysaccharides. Starch is an example of a homopolysaccharide. Hyaluronic acid (in connective tissue) is an example of a heteropolysaccharide.
142
Why is glucose a store of energy?
Glucose is a source of energy, as it is a reactant in respiration. The energy released is used to make ATP, which is the energy currency of the cell. Glucose + oxygen = carbon dioxide + water
143
How do living things store energy?
If you join lots of glucose molecules together into polysaccharides, you can create a store of energy, and this is exactly what living things do. Plants store energy as starch in chloroplasts and in membrane bound starch grains, ans humans store energy as glycogen in cells of the muscles and liver.
144
Why are polysaccharides a good store of energy to do with the amount an organism can store?
The structure of polysaccharides lends itself to energy store. Glycogen and starch are compact, which means they do not occupy a large amount of space. They both occur in dense granules within the cell.
145
How are polysaccharides stored in plants and animals?
Glycogen in animals and starch in plants (comprising amylose and amylopectin) occur within cells in the form of large granules.
146
Why is polysaccharides good energy stores - how does the structure of a polysaccharides structure?
Polysaccharides hold glucose molecules in chains, so they can be easily 'snipped off' from the end of the chain by hydrolysis when required for respiration . Hydrolysis reactions are always catalysed by enzymes. Some chains are unbranched (amylose) and some are branched (amylopectin and glycogen), Branched chains tend to be more compact, but also offer the chance for lots of glucose molecules to be snipped off by hydrolysis at the same time, when lots of energy is requires quickly..
147
What enzymes are responsible for hydrolysing glycosidic linkages?
The enzyme amylase is responsible for hydrolysing 1-4 glycosidic linkages, and glucosidase is responsible for hydrolysing 1-6 glycosidic linkages. A 1-4 glycosidic linkage is one between carbon 1 of one glucose and carbon 4 of the other. (diagram pg 56)
148
Polysaccharides are less soluble in water than monosaccharides, why is this a benefit?
If many glucose molecules did dissolve in the cytoplasm, the water potential would reduce, and excess water would diffuse in, disrupting the normal workings of the cell. Polysaccharides are less soluble because of their size, but also because regions which could hydrogen-bond with water are hidden away inside the molecule. Sometimes the amylose molecule may form a double helix, which presents a hydrophobic external surface in contact with the surrounding solution.
149
State the type of polysaccharide and detailed structure for amylose (in plants).
This molecule is a long chain of alpha glucose molecules. Like maltose, it has glycosidic bonds between carbons 1 and 4. Amylose coils into a spiral shape, with hydrogen bonds holding the spiral in place. Hydroxyl groups on carbon 2 are situated on the inside of coil, making the molecule less soluble and allowing hydrogen bonds to form to maintain the coils structure.
150
State the type of polysaccharide and detailed structure for Amylopectin (in plants).
This is like amylose, with glycosidic bonds between carbons 1 and 6. Amylopectin also coils into a spiral shape, held together with hydrogen bonds, but with branches emerging from the spiral.
151
State the type of polysaccharide and detailed structure for glycogen (in animals).
This molecule is like amylose, with glycosidic bonds between carbon 1 and 4, and branches formed by glycosidic bonds between carbon 1 and 6. The 1-4 bonded chains tend to be smaller than in amylopectin, so glycogen has less tendency to coil. However, it does have more branches, which makes it more compact. And it is easier to remove monomer units as there are more ends.
152
Where is glycogen stored?
Glycogen is stored in the liver and in muscle cells. It may form up yo 7% of the mass of the liver.
153
Does the whole of a glycogen molecule get broken down by hydrolysis?
The core of glycogen or amylopectin molecule is resistant to hydrolysis by enzymes. Such unit is called a limit dextrin, and is one of the major components of mucus.
154
Where is cellulose found?
Cellulose is found in plants, forming plant cell walls. It is a tough, insoluble and fibrous substance.
155
What is cellulose made up of?
Cellulose is a homopolysaccharide made from long chains of up yo 15000 beta-glucose molecules, bonded together through condensation reactions to form glycosidic bonds.
156
How is cellulose formed of beta glucose molecules?
Two beta-glucose molecules line up, the second molecules is rotated forwards 180 degrees compared to the first. Water is removed and a glycosidic bond forms. The chains of beta-glucose that are joined by condensation reaction are straight.
157
Rather than spiralling like chains of alpha-glucose, cellulose chains are straight and lie side by side. This difference in structure is a direct result of bonding. (there are three reasons)
Hydrogen and hydroxyl groups on carbon 1 are inverted in beta-glucose (as compared with alpha-glucose). This means that every other beta-glucose molecule in the chain is rotated by 180 degrees. This and the beta-1-4 glycosidic bond help to prevent the chain spiralling. Hydrogen bonding between rotated beta-glucose molecules in each chain also gives the chain additional strength, and stops it spiralling. Hydrogen bonding between rotated beta-glucose molecules in different chains gives the whole structure additional strength. The hydroxyl group on carbon 2 sticks out, enabling hydrogen bonds to be formed between chains. (diagram on page 59)
158
How are plant cell walls formed?
When 60 to 70 cellulkose chains are bound together in this way, they form microfibrils, which are 10-30 nm in diameter. These then bundle together into macrofibrils containing up to 400 microfibrils, which are embedded in pectins (like glue) to form plant cell walls. The macrofibrils are embedded in pectins to form the cell wall. Macrofibrils run in all directions criss-crossing the wall for extra strength. Hydrogen bonds form between the cellulose chains adding tot he strength of the structure. (diagram on page 59)
159
Why is cellulose is an excellent material for plant cell walls:
Microfibrils and macrofibrils have very tensile strength, both because of the strength of the glycosidic bonds but also because of the hydrogen bonds between chains. Macrofibrils are stronger than steel wire of the same diameter. Macrofibrils run in all directions, criss-crossing the wall for extra strength. It is difficult to digest cellulose because the glycosidic bonds between the glucose molecules are less easy to break. Indeed, most animals do not even have an enzyme to catalyse the reaction.
160
Why does cellulose need to be strong?
Because plants do not have a rigid skeleton, each cell needs to have strength to support the whole plant.
161
What does space between macrofibrils in cellulose allow?
There is space between macrofibrils fr water and mineral ions to pass on their way into and out of the cell. This makes the cell wall fully permeable.
162
What strength does cellulose have that allows the cell to support the structure of the plant, and how does this benefit the plant?
The wall has high tensile strength, which prevents plant cells from bursting when they are turgid, again helping to support the whole plant. Turgid cells press against each other, supporting the structure of the plant as a whole. The wall also protects the delicate cell membrane.
163
What can the macrofibril structure be reinforced with and why?
The macrofibril structure can be reinforced with other substances for extra support to make the cell walls water-proof. For example, cutin and suberin are waxes that block the spaces in the cell wall, and make it waterproof. Lignin (a polymer of phenylpropane units) performs the same function for xylem vessels. In the woody part of the tree trunks, cell walls are extra thick to withstand the weight.
164
Is cellulose used as a food source?
The only vertebrates to use cellulose as food are cattle and other ruminants, like sheep, goats, camels and giraffes. Microorganisms which live in their digestive system produce an enzyme called cellulase, which helps break down cellulose.
165
How has the structural strength of cellulose been exploited by humans?
Cotton is 90% cellulose. Cellophane and celluloid (which used to be used in photographic film) are also derived from cellulose. One of the main components of paper is cellulose. Rayon (viscose) is a semi-synthetic fibre produced from cellulose. It has similar properties to those made of silk.
166
Describe bacterial cell walls.
Bacteria also have cell walls, but they are not made of cellulose. The whole structure surrounding the cell is called a peptidoglycan, made from long polysaccharide chains that lie in parallel, cross-linked by short peptide chains (made of amino acids).
167
Describe how polysaccharides vary for exoskeletons.
Insect and crustacean exoskeletons are made of chitin. It differs from cellulose because it has an acetylamino group (NH.OCCH3) rather than a hydroxyl group n carbon 2. It forms cross-links between long parallel chains of acetylglucosamine, in a similar way to cellulose.
168
What is a lipid?
A group of substances that are soluble in alcohol rather than water. They include triglycerides, phospholipids, glycolipids and cholesterol.
169
What is a macromolecule?
A very large, organic molecule.
170
What is a phospholipid?
A molecule consisting of glycerol, two fatty acids and one phosphate group.
171
What elements do lipids contain?
Lipids contain large amounts of carbon and hydrogen, and smaller amounts of oxygen.
172
Why are lipids insoluble in water?
They are insoluble in water because they are not polar, and so do not attract water molecules, but do dissolve in alcohol.
173
What are the three most important lipid in living things?
The three most important lipids in living things are triglycerides, phospholipids, and steroids. These are not polymers, but they do have different components bonded together. They are examples of macromolecules.
174
What are triglycerides made of and how does the body acquire them?
Triglycerides are made up of glycerol and fatty acids. There are many different types of fatty acid. We can make many of them in our bodies, but some must be ingested complete. These are essential fatty acids.
175
What is the structure of glycerol?
Glycerol has three carbon atoms. It is an alcohol, which means it has free -OH groups. There are three -OH groups, which are important to the structure of triglycerides. (displayed formula on page 61)
176
What is the structure of fatty acids?
Fatty acids have a carboxyl group (COOH) on the end, attached to a hydrocarbon tail, made of only carbon a hydrogen atoms.
177
What is the chain length of fatty acids?
Anything from 2 to 20 carbons long.
178
What does the carboxyl group of hydrocarbons ionise into?
The carboxyl group ionises into H+ and -COO- group. This structure is therefore an acid because it can produce free H+ ions.
179
What does it mean if a fatty acid is saturated?
If a fatty acid is saturated this means that there are no C=C bonds in the molecule. If a fatty acid is unsaturated, there is a double bond between two of the carbon atoms instead, which means that fewer hydrogen atoms can be bonded to the molecule.
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What does a single C=C bond in a fatty acid make it?
Monosaturated, e.g. oleic acid.
181
What does more than one C=C bond make a fatty acid?
Polyunsaturated, e.g. linoleum acid.
182
What gives unsaturated fats a lower melting point than saturated fats?
Having one or more C=C bond changes the shape of the hydrocarbon chain, giving it a kink where the double bond is. Because these kinks push molecules apart slightly, it makes them more fluid. Animal lipids contain a lot of saturated fatty acids, which are often solid at 20 degrees. If there are more unsaturated fatty acids, the melting point is lower.
183
Where does the condensation bond form in a triglyceride?
A triglyceride molecule consists of one glycerol molecule bonded to three fatty acids. A condensation reaction happens between the -COOH group of the fatty acid and the -OH group of the glycerol. Because there are three -OH groups, three fatty acids will bond, hence the name triglyceride.
184
What is the the bond in a triglyceride, between the glycerol and the fatty acid known as?
Because it is a condensation reaction, a water molecule is produced, and the covalent bond formed is known as an ester bond. In some cases, the same type of fatty acid may bond to each -OH group, or the fatty acids may be different.
185
State the type of reaction, the bond broken and molecules used for fatty acids joining and separating from glycerol. (diagram on page 62)
When a fatty acid tail joins to glycerol it is a condensation reaction, an ester (covalent) bond is formed and a water molecule is eliminated. When a triglyceride separates it is a hydrolysis reaction, an ester (covalent) bond is broken, and a water molecule is used up.
186
What are the different functions of triglyceride's?
As an energy store, and energy scource, insulation, buoyancy and protection.
187
Describe the function of triglyceride's as an energy scource.
Triglyceride's can be broken down in respiration to release energy and generate ATP. The first step is to hydrolyse the ester bonds, and then both glycerol and the fatty acids can be broken down completely to carbon dioxide and water. Respiration of a lipid produces more water than respiration of sugar.
188
Describe the function of triglyceride's as an energy store.
Because triglyceride's are insoluble in water, they can be stored without affecting the water potential of the cell. Mammals store fat in adipose cells under the skin. One gram of fat releases twice as much energy as one gram of glucose. This is because lipids have a higher proportion of hydrogen atoms than carbohydrates, and almost no oxygen atoms.
189
Describe the function of triglyceride's as insulation.
Adipose tissue is a storage location for a lipid in whales ('blubber'), acting as a heat insulator. Lipid in nerve cells acts as an electrical insulator. Animals preparing for hibernation store extra fat.
190
Describe the function of triglyceride's as buoyancy.
Because fat is less dense than water, it is used by aquatic mammals to help them stay afloat.
191
Describe the function of triglyceride's as protection.
Humans have fat around delicate organs, such as their kidneys, to act as a shock absorber. The peptidoglycan cell wall of some bacteria is covered in a lipid-rich outer coat.
192
How may lipids be used to protect an organism from water?
Insects and leaves are covered in wax to help make them waterproof. waxes are a type of lipid formed by combining fatty acids with alcohol molecules much larger than glycerol.
193
What do glycosidic, peptide and ester bonds all involve?
They all involve condensation, but each is specific to the particular biomolecules they link together.
194
What is the difference between triglycerides and phospholipids?
Phospholipids have the same structure as triglycerides except that one of the fatty acids is replaced by a phosphate group.
195
What forms an ester bond in a phospholipid?
A condensation reaction between an OH group on a phosphoric acid molecule (H3PO4) and one of the three -OH groups on the glycerol forms an ester bond.
196
What is the usual chain length of phospholipids?
Most of the fatty acids found in phospholipids have an even number of carbon atoms (often 16 or 18). Commonly one of these chains is saturated and one of them is unsaturated. (diagram page 63)
197
How do phospholipids behave in water?
When surrounded by water, the phosphate group has a negative charge, making it polar (attracted to water). However, fatty acid tails are non-polar and so are repelled by water. It is common to refer to the head as hydrophilic and the tail as hydrophobic, which means that the phospholipid molecule is amphipathic.
198
What distinct properties do phospholipids have in water?
They may form a layer on the surface of the water with heads in the water and tails sticking up out of the water. They may also form micelles - tiny balls with tails tucked away inside, and the heads pointing outwards into the water. (diagram of micelle on page 63)
199
What type of lipids are amphipathic?
Membrane lipids tend to be amphipathic, whereas those involved in storage are not.
200
What are amphipathic phospholipids excellent at?
Amphipathic phospholipids are excellent at forming membranes around cells and organelles. Inside and outside a cell membrane is an aqueous solution. The phospholipids form a bi-layer, with two rows of phospholipids, tails pointing inwards and heads pointing outwards into the solution.
201
How many membranes in plant and animal cells are made of phospholipids?
Between 20 and 80% of membranes in plant and animal cells are made of phospholipids
202
What do bacterial membranes contain more of than plant membranes?
Bacterial membranes tend to contain a greater proportion of protien.
203
Are phospholipids within membranes stationary?
The individual phospholipids are free to move around in their layer, but will not move into any position where their hydrophobic tails are exposed to water. This gives the membrane some stability.
204
How permeable is the phospholipid bi-layer?
The membrane is selectively permeable. it is only possible for small non-polar molecules to move through the tails in the bilayer, such as oxygen and carbon dioxide. This lets the membrane control what goes on in and out of the cell, and keeps it functioning properly.
205
What is cholesterol and what does it consist of?
Cholesterol (chole-sterol) is a steroid - a type of lipid which is not made from glycerol or fatty acids. It consists of four carbon-based rings or isoprene units.
206
What does cholesterol do in a membrane?
Cholesterol is a small and hydrophobic molecule, which means it can sit in the middle of the hydrophobic part of the bilayer. It regulates the fluidity of membrane, preventing it from becoming too fluid or stiff.
207
Where is cholesterol made?
Cholesterol is mainly made in the liver in animals. Plants also have a cholesterol derivative in their membranes. It is called stigmasterol, and is different from cholesterol in only one respect: it has a double bond between carbon 22 and carbon 23.
208
What hormones are made of cholesterol?
The steroid hormones testosterone, oestrogen and vitamin D are all made from cholesterol.
209
Why can steroids pass through phospholipid membranes?
Because they are small and hydrophobic, they can pass through the hydrophobic part of the cell membrane and any other membrane inside the cell.
210
Where are steroids abundant apart from the body?
Steroids are also abundant in plants, and on ingestion and absorption some can be converted into animal hormones.
211
Name a poison made from steroids.
Digitalis is a cardiac poison.
212
Describe another class of lipids found in plants.
Plants have another class of lipids called terpenes. these are like steroids, being constructed of isoprene units.
213
Give some examples of terpenes.
Examples include gibberellins (a plant growth substance), carotenoids (a photosynthetic pigment) and phytol (a component of chlorophyll.
214
What is a fibrous protein?
Has a relatively long, thin structure, is insoluble in water and metabolically inactive, often having a structual role within an organism.
215
What is a globular protien?
Has molecules of a relatively spherical shape, which are soluble in water and often have metabolic roles within the organism.
216
What is a prosthetic group?
A non-protien component that forms a permanent part of a functioning protien molecule.
217
The three dimensional tertiary and quaternary structure of protien falls into which categories?
Fibrous and globular proteins, they do different jobs, and so have different properties.
218
Describe fibrous proteins.
Have regular, repetitive sequence of amino acids, and are usually insoluble in water. these features enable them to form fibres, which tend to have a structual function. Examples include collagen and elastin (in connective tissue) and keratin (in hair).
219
Describe a globular protien, and how they are formed.
Globular proteins tend to roll up into an almost spherical shape. Any hydrophobic R groups are turned inwards towards the centre of the molecule, while hydrophilic groups are on the outside. They often have very specific shapes, which helps them to take up roles as enzymes, hormones (such as insulin) and haemoglobin.
220
Are globular proteins soluble?
This makes the protien water soluble, because water molecules can easily cluster round and bind to them.
221
What is the function of collagen?
To provide mechanical strength.
222
What is the purpose of collagen within artery walls?
A layer of collagen prevents the artery bursting when withstanding high pressure from blood being pumped by the heart.
223
Where is collagen used to work with your bones?
Tendons are made of collagen and connect muscles to bones, allowing them to pull on bones. Bones are made from collagen, and then reinforced with calcium phosphate, which makes them hard. Cartilage and connective tissue are made from collagen.
224
What is keratin?
Keratin is rich in cysteine so lots of disulphide bridges form between its polypeptide chains. Alongside hydrogen bonding, this makes the molecule very strong.
225
Where is keratin found?
Keratin is found wherever a body part needs to be hard and strong. It is found in finger nails, hair, claws, hoofs, horns, scales, fur and feathers.
226
What does keratin provide?
It provides mechanical protection, but also provides an impermeable barrier to infection, and, being waterproof, also prevents entry of water-borne pollutants.
227
Where is elastin found?
In living things where they need to stretch or adapt their shape as part of life processes.
228
Describe the structure of elastin.
Cross-linking and coiling make the structure of elastin strong and extensible.
229
In our bodies where does elastin help organs stretch?
Skin can stretch around our bones and muscles because of elastin. Without elastin, skin would not go back to normal after being pinched.
230
In our bodies where does elastin help organs inflate and deflate?
Elastin in our lungs allows them to inflate and deflate, and in our bladder helps it to expand to hold urine. Like collagen, elastin helps our blood vessel to stretch and recoil as blood is pumped through them, helping maintain the pressure wave of blood as it passes through.
231
What is the quatenery structure of haemoglobin made up of?
Four polypeptides; to alpha-goblin chains and two beta-goblin chains. Each one of these has its own tertiary structure, but when fitted together they form a haemoglobin molecule.
232
Where is the haem group positioned within the structure within a haemoglobin molecule?
The interactions between the polypeptides give the molecule a very specific shape. At one position on the outside of each chain, there is a space in which one haem group is held. Groups like this are called prosthetic groups.
233
What is the purpose of prosthetic groups?
They are an essential part of the molecule, without which it could not function, but they are not made of amino acids. The haem group contains an iron ion.
234
What is a protien associated with prosthetic groups?
A protien associated with this kind of group is called a conjugated protien.
235
What is the function of haemoglobin?
The function go of haemoglobin is to carry oxygen from the lungs to the tissues.
236
What happens to haemoglobin as it passes through the lungs?
In the lungs, an oxygen molecule binds to the iron in each of four harm groups in the haemoglobin molecule. When it binds, haemoglobin turns from a purple red colour to bright red. The oxygen is released by the haemoglobin when it reaches the tissues.
237
What is the structure of insulin?
Insulin is made of two polypeptide chains. The chain A begins with a section o alpha-helx, and the B chain ends with a section of Beta-pleat. Both chains fold into a tertiary structure, and are then joined together by disulphide links.
238
How does insulin create the desired effect?
Insulin binds to glycoprotein receptors on the outside of muscle fat cells to increase their uptake of glucose from the blood, and to increase their rate of consumption of glucose.
239
Why can insulin be transported around the body?
Amino acids with hydrophilic R groups are on the outside of the molecule, which makes it soluble in water.
240
What is pepsin?
Pepsin is an enzyme that digests protein in the stomach..
241
What is the structure of pepsin?
The enzyme is mad up of a single polypeptide chain of 327 amino acids, but it folds into a symmetrical tertiary structure
242
Why is pepsin stable in the acidic environment of the stomach?
Pepsin has very few basic R groups (only 4) whereas it has 43 amino acids with acidic R groups. This helps explain why it is so stable in the acidic environment of the stomach, as there are very few basic groups to accept H+ ions, and therefore there can be little effect on the enzymes structure.
243
How is the terry structure of pepsin held together?
by hydrogen bonds and two disulphide bridges.
244
Why is computer modelling of protein structure useful?
Being able to predict the shape of a protein molecule formats primary structure can be incredibly useful in biochemistry. For example, predicting the occurrence of biologically active binding sites on a portion molecule can help in identifying new medicines.
245
Scientists can predict protein shapes using computer modelling techniques. What is this prediction based on?
As techniques for prediction of secondary developed, they were based upon the probability of an amino acid or sequence of amino acids, being in a particular secondary structure. Such probabilities were derived from 'already known' protein molecular structures.
246
Computer modelling of a protein structure: why is computer modelling of a tertiary structure usually more useful than the prediction of protein shapes?
It is usually the tertiary structure of a protein molecule which contributes directly to its bioactive function.
247
What are the two broad approaches of protein modelling tertiary structures?
Ab initio protein modelling and comparative protein modelling.
248
Describe Ab initio protein modeling.
In this approach, a model is built based on the physical and electrical properties of the atoms in each amino acid in the sequence. With this technique, there can be multiple solutions to the same amino acid sequence, and other methods sometimes need applying to reduce the number of solutions.
249
Describe comparative protein modeling.
One approach is protein threading, which scans the amino acid sequence against a database of solved structures and produces a set of possible models which would match the sequence.
250
Inorganic ions are essential constituents of skeletal structures, what are they involved in?
The maintenance of osmotic pressure and are structural constituents of soft tissue. They are also important for nerve impulse transmission and muscle contraction, and play a vital role in maintaining the pH balance of the body. They serve as essential components and activators of enzymes, vitamins and hormones.
251
Cations; Describe the importance of calcium Ca2+ in biological processes. (Try to look for pattens when learning the roles of these ions. Pick out those with similar functions, or relate the function to biology you have studied.)
Increases rigidity of bone, teeth and cartilage and is a component of the exoskeleton of crustaceans. Important in clotting blood and muscle contraction. Activator for several enzymes, such as lipase, ATPase and cholinesterase. Stimulates muscle contraction and regulates permeability of cell membranes. Important for cell wall development in plants, and formation of middle lamella between cell walls.
252
Cations; Describe the importance of sodium Na+ in biological processes.
Involved in regulation of osmotic pressure, control of water levels in body fluid and maintenance of pH. Affects absorption of carbohydrate in the intestine, and water in the kidney. Contributes to nervous transmissions and muscle contraction. Constituent of vacuole in plants which helps maintain turgidity.
253
Cations; Describe the importance of Potassium K+ in biological processes.
Involved in control of water levels in body fluid and maintenance of pH. Assists active transport of materials across the cell membrane. Involved in synthesis of glycogen and protien, and the breakdown of glucose. Generates healthy leaves and flowers in flowering plants. Contributes to nervous transmission and muscle contraction. Component of vacuoles in plants, helping to maintain turgidity.
254
Cations; Describe the importance of hydrogen H+ in biological processes.
Involved in photosynthesis and respiration. Involved in transport of oxygen and carbon dioxide in the blood. Involved in the regulation of blood pH.
255
Cations; Describe the importance of ammonium NH4+ in biological processes.
A component of amino acids, proteins, vitamins and chlorophyll. Some hormones are made of proteins, e.g. insulin. An essential component of nucleic acids. Involved in maintenance of pH in the human body. A component of the nitrogen cycle.
256
Anions Describe the importance of nitrate NO3- in biological processes.
A component of amino acids, proteins, vitamins and chlorophyll. An essential component of nucleic acids. Some hormones are made of proteins, which contain nitrogen, e.g. insulin. A component of the nitrogen cycle.
257
Describe the importance of hydrogencarbonate HCO3- in biological processes.
Involved in regulation of blood pH. Involved in transport of carbon dioxide into and out of the blood.
258
Describe the importance of chloride Cl- in biological processes.
Helps in production of urine in the kidney, and maintaining water balance. Involved in transport of carbon dioxide into and out of the blood. Regulates affinity of haemoglobin to oxygen through allosteric effects on the haemoglobin molecule. Involved in regulation of blood pH. Used to produce hydrochloric acid in the stomach.
259
Describe the importance of phosphate PO43- in biological processes.
Increases rigidity of bone, teeth and cartilage and is a component of the exoskeleton of crustaceans. Component of phospholipids, ATP, nucleic aids and several important enzymes. Involved in regulation of blood pH. Helps root growth in plants.
260
Describe the importance of hydroxide OH- in biological processes.
Involved in regulation of blood pH.
261
What is added to toothpaste, especially children's toothpaste, to improve bones and teeth?
fluorine, and calcium fluoride is important for bone and teeth.
262
In humans and plants what are ions required in large amounts called and what are ions required in small amounts called?
Ions required in small amounts are micronutrients or trace elements. Ions required in large amounts are called macronutrients or main elements.
263
What happens if not enough of a particular ion is consumed?
Both humans and plants can display deficiency symptoms if they do not consume enough of a particular ion. For example, deficiency of the trace element cobalt causes anaemia, while deficiency of copper in plants causes young shoots to die back.
264
What do qualitative tests determine?
The presence or absence of the particular biological molecule.
265
What do qualitative food tests rely on?
The biological molecules in the sample passing into solution. Therefore you will need to grind and squash the food samples first, and then mix them vigorously with a small volume of water (or in the case of lipids, alcohol)
266
What do you need to wear when carrying out qualitative tests for biological molecules?
Eye protection.
267
Describe the test for starch.
To test for starch, add iodine solution (in potassium iodide) to sample. If starch is present, you will see a colour change of yellow-brown to blue-black. When dissolved in potassium iodide, the iodine (I2) forms a triiodide ion I3- which slips into the middle of the amylose helix. This causes the colour to change.
268
Give an example of where the iodine test is used.
The iodine test disused in brewing to check any chains of glucose in the fermentation mix are relatively short, if longer chains go into the fermentation mix they give the final beer a haze, which looks unappealing. Longer chains yield a blue-black result with iodine, whereas shorter chains give no colour change, or a much less intense red-purple colour. (more info on page 74)
269
What do reducing sugars include?
These include all monosaccharides and some disaccharides.
270
Why are reducing sugars known as reducing sugars?
Because they can reduce, or give electrons to, other molecules.
271
What is the test for reducing sugars?
Place a sample of food to be tested in a boiling tube. Add Benedict's solution ten heat in water bath at 80 degrees for 3 minutes. Orange-red precipitate indicates a reducing sugar is present (when low levels of sugar are present, the contents of the boiling tube may appear yellow or green.
272
What forms the colour in reducing sugars?
Benedict's solution contains Cu2+ ions, which are reduced to Cu+ ions, forming orange-red copper (I) oxide (Cu2O). This is called a precipitate because it comes out of solution and forms a solid suspended in the reaction mixture.
273
What will happen if different amounts of blue benedicts solution in the test for reducing sugars?
If you use blue benedicts solution in excess, the intensity of the red colour is proportional to the concentration of sugar. The reaction mix will appear green if only a little precipitate is formed, and fully orange-red if a lot of precipitate is formed.
274
What is a different form blue benedicts comes in and how can this be used?
It is also possible to use commercially manufactured test strips to test for reducing sugars. here you simply dip the strip into the test solution, and compare the colour with the calibration card supplied. This tells you whether reducing sugar is present or absent from your solution.
275
Where is manufactured test strips of blue benedicts often used?
They are often used to test for glucose in the urine of diabetic patients.
276
How do you test for a non-reducing sugar?
To test for a non-reducing sugar, we have to hydrolyse the bond first, to 'free up' these 'reducing groups' and then test for reducing sugars as normal; First, test a sample for reducing sugars to check there are none there in the first place. Take a separate sample and boil it with hydrochloric acid to hydrolyse the sucrose into glucose and fructose. Cool the solution and use sodium hydrogencarbonate solution to neutralise it. Test for reducing sugars again.
277
What does a positive result of a non-reducing sugars test indicate?
A positive result (green-yellow-orange-red) indicates that non-reducing sugar (e.g. sucrose) was present in the original sample..
278
Why may you need to do another test after a positive test for reducing sugars?
In some cases, a sample may contain reducing and non-reducing sugars.
279
If a sample may contain reducing and non-reducing sugars how will the results of each tests compare?
If you have a positive test for reducing sugars from your first sample, you can go on to test for non-reducing sugars in an equal-sized seconds sample. If present, the precipitate from this second sample will have more mass than the precipitate from the first sample. You can extract the precipitate from the mixture by filtration.
280
What are the steps of the test for lipids?
Take a sample and mix it thoroughly with ethanol. Any lipid will go into solution in the ethanol (remember that lipids are not soluble in water) Filter Pour the solution into water in a clean test tube. A cloudy white emulsion indicates the presence of lipids. This is made of tiny lipid droplets that come out of solution when mixed with water. (diagram on page 75)
281
What test do you use for the test for proteins?
The biuret test.
282
In the biuret test what will the colour change be for a positive test?
If protien is present, the colour changes from light blue to lilac.
283
What is the procedure for testing for proteins with biuret reagent?
Add 2 cm3 of the liquid food sample\* to a clean, dry test tube Add 2 cm3 of Biuret Reagent. Repeat steps the steps above with de-ionized water to prepare a negative control and with albumin (egg white) to prepare a positive control. Shake well and allow the mixture to stand for 5 minutes Observe any colour change.
284
When testing for protein how does the solution change colour?
The colour is formed by a complex between the nitrogen atoms in a peptide chain and Cu2+ ions, which is why this test really detects the presents of peptide bonds.
285
How may reagents be supplied if it does not come as biuret reagent?
You may find the reagents are supplied to you separately as biuret A (sodium hydroxide), which you add first, and biuret B (copper sulfate), which you add next.
286
What is the procedure for the Biuret Test for protein using sodium hydroxide and copper sulphate solutions?
Add 1 cm3 of sodium hydroxide solution (40% or bench solution) and 1% copper (II) sulphate solution dropwise (one drop at a time) to the food sample Repeat the steps above with de-ionized water to prepare a negative control and with albumin (egg white) to prepare a positive control. Shake well and allow the mixture to stand for 5 minutes Observe any colour change.
287
Benedicts solution detects the presents of reducing sugars. What happens if there is more sugar present and how can we try to quantify the concentration of sugar in the original solution?
The amount of precipitate will increase. The amount of copper (II) ions remaining in solution will decrease. We can try to quantify the concentration of sugar in the original solution by assessing how these tow variables change, using a technique called calorimetry.
288
How does a calorimeter work?
A colorimeter works by shining light through a sample. In the case, we would use a centrifuge to separate the precipitate and any excess benedicts solution (the supernatant).
289
When using a calorimeter to quantify the concentration of sugar in sample what is placed into the calorimeter?
Using a pipette, we can take the supernatant and place it in a cuvette (a small vial), which is then placed into the calorimeter. The cuvette is commonly made out of glass or plastic. Ensure you do not leave a greasy fingerprint on the surface of the cuvette, as it could affect the transmission of light.
290
How can the calorimeter achieve a greater accuracy?
Colour filters are often used for greater accuracy. By using a red filter in this case, we can shine red light through the solution, and detect how much passes through (percentage transmission). The solution reflects blue light but absorbs red lights.
291
When trying to quantify the concentration of sugar in the original solution by assessing how these tow variables change, using calorimetry how will the results change with different concentrations of unreacted copper sulfate?
If there is a lot of unreacted copper sulfate, the supernatant is still quite blue, absorption of red light is high and percentage transmission is low. If there is little unreacted copper sulfate, the supernatant is less blue, absorption of red light is low and percentage transmission is high.
292
When using a colorimeter what happens between each reading?
The device is usually zeroed between each reading by placing an appropriate 'blank'sample to reset the 100% transmission/absorption. In the case of quantifying the concentration of sugar, the blank used would be water.
293
In a calorimeter what receives the light rays?
A photo-electric cell.
294
In what other form do calorimeters come, apart from using light?
Colorimeters can also be used with UV light. Instead of plastic or glass the cuvettes are made of quartz.
295
Why would you create a calibration curve? (quantitative test for reducing sugar)
Using a calorimeter gives us a semi-quantitative test for sugar, as we can compare how much sugar is contained within different samples. to find exact amounts, we need to create a calibration curve.
296
How do you create a calibration curve? (quantitative test for reducing sugar)
First, take a series of known concentrations of reducing sugar. Using a sample of each, carry out a benedicts test. Use a colorimeter to record the percentage transmission of light through each supernatant. Plot a graph to show 'transmission of light' against the concentration of reducing sugar. This provides a calibration curve.
297
How can the calibration curve be used? (quantitative test for reducing sugar)
You can use it with other 'unknown' samples to determine the concentration of sugar in the original sample. Foe example, using the calibration curve if a sample of glucose has a transmission of 92%, we can conclude that it contains 12 g dm-3 of glucose. (graph on page 77)
298
How can the results from a colorimeter be presented?
It is possible to express results from a colorimeter as a percentage transmission or percentage absorption. It is very important to know which form is used in order to interpret results appropriately. (100% transmission = 0% absorption).
299
How do biosensors work?
They take a biological or chemical variable which cannot easily be measured, and convert it to an electrical signal.
300
Describe the process of an output being produced from a biosensor.
In the binding event molecules to be measured binds to the receptors on the biological layer, which is connected to the transducer. In the transducer the electrical signal passes from the transducer surface to the electronics. In the signal conditioner the electrical signal is passed through the electronics and formed as an output. (diagram on page 77)
301
Give some examples of biosensors.
Biosensors have many other applications. For example, they can be used top detect contaminant s in water, and pathogens and toxins in food. They can even be used to detect airborne bacteria, for example in counter-bioterrorism programmes.
302
What was one of the first examples of a biosensor?
Carrying a canary into the mine. As toxic gasses built up, the canary died, providing the miners with an early warning to evacuate the mine. A new nanocanary has now been produced which aims to assess the toxicity of bioengineered nanomaterials on living cells.
303
What is the aim of chromatography?
The aim of chromatography is to separate a mixture into its components: in this case biological molecules.
304
What are two key components of chromatography?
The stationary phase and the mobile phase.
305
Describe the stationary phase of chromatography.
This is either the chromatography paper or a thin-layer chromatography (TLC) plate. The paper is made of cellulose. The TLC plate is often a sheet of plastic, coated with a thin layer of silica gel or aluminium hydroxide. In each case, there are free -OH groups pointing outwards, in contact with the mobile phase.
306
Describe the mobile phase of chromatography.
This is the solvent for the biological molecules. At a simple level, we can use water (for polar molecules) or ethanol (for non-polar molecules). The mobile phase flows through and across the stationary phase, carrying the biological molecules with it.
307
How would you set up thin-layer chromatography? (although paper chromatography would be set up in the same way. (diagram on page 78)
Wear eye protection. Draw a line in pencil and put a tiny dot on the line to show you where to place your solution mixture. If you draw it in ink, the pigments in the ink will also separate. Spot the solution mixture onto the pencil dot several times by using capillary tubing. Wait for the spot to dry before putting on the next spot, and try to make the spot as thin as possible. When it is completely dry, lower it into the solvent. Ensure the level of the solvent at the start is below the pencil line. Cover the beaker with a watch glass, or glass plate.
308
What happens to the spots of mixture in chromatography?
As the solvent travels up the paper or plate, the component of the solution mixture travel with it. In the example of separating the pigments in an ink you can see that they travel at different speeds. by the time the solvent has reached the top of the plate, some are travelling slowly and some quickly, and so are at different positions on the plate.
309
How can you identify the pigments in chromatography?
You can use the relative distance travelled to help identify the pigments. Calculate the Rf value by measuring the distance from the pencil line to the centre spot of the pigment (x), and the distance from the pencil line to the solvent front (y) (do not forget to do this before the solvent dries so you can still see it).
Rf = x/y
310
How do you know the Rf of pigments of identified substances in chromatography?
If you repeat the investigation under the same conditions, each pigment will always the the same Rf value. If you know the Rf values of particular pigments under these conditions, this allows you to identify them. Exactly the same is true of biological molecules.
311
Sometimes with colourless molecules, you cannot see where they finish. Using thin-layer chromatography what are the solutions?
Ultraviolet light, ninhydrin and iodine.
312
Sometimes with colourless molecules, you cannot see where they finish describe ultraviolet light as a solution.
Thin layer chromatography plates have a chemical which fluoresces under UV light. If you look at the plate under UV light, most of it will glow except those places where the spots have travelled to. They mask the plate from the UV light.
313
Sometimes with colourless molecules, you cannot see where they finish describe ninhydrin as a solution.
To see amino acids, allow the plate to dry, and then spray it with ninhydrin. This binds to the amino acids which are then visible as brown or purple spots.
314
Sometimes with colourless molecules, you cannot see where they finish describe iodine as a solution.
Allow the plate to dry to dry, and place in an enclosed container with a few iodine crystals. the iodine forms a gas, which then binds to the molecules in each of the spots.
315
What does the spped at which molecules move along the p;aper or TLC plate depend on?
Their solubility in the solvent, and their ploarity. In the case of paper chromatography, it may also depend on their size.
316
What moves faster along chromatography paper, polar or non-polar substances?
A highly polar solute will tend to stick to the surface (it is absorbed), and hence moves more slowly. A non-polar solute will travel very quickly up the plate.
317
What makes non-polar substances travel quicker up chromatography paper that polar substances?
Exposed -OH groups make the surface of the paper or plate very polar, and allow it to form hydrogen bonds with the molecules, alongside other dipole interactions. A highly polar solute will tend to stick to the surface (it is absorbed), and hence moves more slowly. A non-polar solute will travel very quickly up the plate.
318
How is chromatography used?
Thin layer chromatography is commonly used to monitor the progress of reactions, because it works relatively quickly. It is also used for urine testing of athletes for illegal drugs, analysing drugs for purity of components, and analysis of foods to determine the presence of contaminants.
