Chapter 2: Biological Molecules Flashcards
(120 cards)
1
Q
What is the monomer of a polysaccharide?
A
Monosaccharide.
2
Q
What are the monomers of nucleic acids?
A
Monosaccharides and nucleotides.
3
Q
What is the monomer of a protein?
A
Amino acids
4
Q
What is a monomer?
A
A monomer is a simple molecule which is used as a building block for the synthesis of polymers. Many monomers are joined together to make the polymer, usually by condensation reactions.
5
Q
What is a polymer?
A
A polymer is a giant molecule made from many monomers joining together, usually by condensation reactions.
6
Q
What is a macromolecule?
A
It is a large biological molecule such as a protein, polysaccharide or nucleic acid.
7
Q
What is the general formula for a carbohydrate?
A
Cx(H2O)y
8
Q
What three groups can carbohydrates be categorised into?
A
Monosaccharides, disaccharides, polysaccharides.
9
Q
What is the general formula for a monosaccharide?
A
(CH2O)n
10
Q
What is a monosaccharide?
A
A monosaccharide is molecule consisting of a single sugar unit that cannot be hydrolysed any further. it is the simplest form of a carbohydrate.
11
Q
What do sugars do when mixed with water?
A
They dissolve easily in water to form sweet tasting solutions.
12
Q
What are monosaccharides with 3C, 5C, 6C called?
A
3C-trioses, 5C-pentoses, 6C-hexoses
13
Q
What do the names of all sugars end with?
A
-ose
14
Q
Name some hexoses. (3)
A
Glucose, fructose and galactose.
15
Q
What are some common pentoses?
A
Ribose and deoxyribose
16
Q
What is one important aspect of pentoses and hexoses?
A
Both have a chain of carbon atoms long enough to close up on itself and form a more stable ring structure.
17
Q
What is the molecular formula for glucose?
A
C6H12O6
18
Q
What are the two isomers of a glucose molecule and explain.
A
Isomers can be defined as having the same molecular formula, but different structural formulae. In a glucose ring structure, where the hydroxyl group is below the ring structure, the molecule is known as a-glucose. Where the hydroxyl group is above the ring structure, the molecule is known as B-glucose. Their difference lies in the position of the hydroxyl group in their ring structures.
19
Q
What are the two roles of monosaccharides in living organisms? Explain. (2)
A
- They are commonly used as a source of energy during respiration due to the large number of C-H bonds. These bonds can be broken to release a lot of energy, which is transferred to help make ATP from ADP and phosphate.
- Monosaccharides are used as building blocks for larger molecules.
20
Q
What is deoxyribose used for?
A
Deoxyribose, a pentose, is one of the molecules used to make DNA.
21
Q
What is ribose used for?
A
Ribose, a pentose, is one of the molecules used to make RNA and ATP.
22
Q
What is a disaccharide?
A
A disaccharide is a sugar molecule consisting of two monosaccharides (two sugar units) joined together by a glycosidic bond.
23
Q
What are some examples of disaccharides?
A
Maltose, sucrose and lactose.
24
Q
What is maltose made up of?
A
glucose+glucose
25
What is sucrose made up of?
glucose+fructose
26
What is lactose made up of?
glucose+galactose
27
What are two functions of sucrose?
Sucrose is the transport sugar found in plants and the sugar commonly found in shops.
28
What is a condensation reaction?
The joining of two monomers involving the formation fo a glycosidic bond and removal of water is known as a condensation reaction.
29
What is a glycosidic bond?
In each condensation reaction, two hydroxyl groups line up alongside each other. One combines with the hydrogen of the other to form a water molecule. This creates an oxygen bridge between the molecules that is known as the glycosidic bond. In conclusion, a glycosidic bond is a covalent bond that is formed through the removal of water in a condensation reaction.
30
What is the most important monosaccharide in energy metabolism?
Glucose
31
What is the reverse of condensation known as?
The break down of polymers can take place by the addition of water in the process of hydrolysis which breaks the glycosidic bond between the monomers.
32
What polysaccharides is glucose used to make?
Starch, glycogen and cellulose.
33
Where is lactose found?
It is the sugar found in milk.
34
What is a polysaccharide?
A polysaccharide is a polymer whose subunits are monosaccharides joined together by glycosidic bonds.
35
Are polysaccharides sugars?
No
36
What are some examples of polysaccharides?
Starch, glycogen and cellulose
37
What features of glucose cause it to be stored in a different form in living organisms and why?
Glucose is a small, reactive molecule that if dissolved in cells, would affect the osmotic properties of the cell. Therefore, to prevent such problems, glucose is converted to a storage polysaccharide.
38
What are some characteristics of polysaccharides?
The are insoluble, compact, inert molecules.
39
To which storage polysaccharide is glucose converted to in plants and animals?
Glucose is converted to starch is plants and glycogen in animals.
40
How can glucose be made available again from the storage polysaccharide?
It can be made available again by an enzyme-controlled reaction.
41
What is starch made up of?
Amylose and amylopectin
42
Describe the structural formula and structure of amylose.
Amylose is made by condensations between 1,4 linked a-glucose molecules producing a long, unbranched chain. The final product consists of curved chains coiling into helical structures making it more compact.
43
Describe the structure of amylopectin.
Amylopectin is made up of 1,4 and 1, 6 linked a-glucose molecules. The chains are shorter than amylose and branch out to the sides formed by 1,6 linkages.
44
Describe the structure of glycogen.
The structure of a glycogen molecule is similar to that of an amylopectin molecule as both have 1,4 and 1,6 a-glucose linkages. However, glycogen molecules tend to be more branched than amylopectin molecules and hence have more 1,6 linkages than amylopectin. Glycogen molecules clump together to form granules.
45
In which cells are glycogen molecules visible?
In liver and muscle cells where they form an energy reserve.
46
Describe the structure of cellulose.
Cellulose is made up of b-glucose molecules where the hydroxyl group is above the ring structure. In order to form 1,4 linked glycosidic bonds between each b-glucose molecule, every alternate b-glucose is rotated 180 degrees.
47
Describe the hydrogen bonding in cellulose molecules.
The arrangement of b-glucose molecules results in a strong molecule because the hydrogen atoms are weakly attracted to the oxygen atoms. The hydrogen bonds are formed between parallel molecules.
48
What are microfibrils?
The hydrogen bonding between parallel cellulose molecules allows 60-70 cellulose molecules to become tightly cross linked to form bundles called microfibrils.
49
What are fibres?
The microfibrils made of 60-70 cellulose molecules tightly cross-linked are in turn held together in bundles called fibres.
50
What two characteristics of the cell wall cause it to have a high tensile strength?
The cell wall has several layers of fibres held together by hydrogen bonding and run in opposite directions, increasing the strength.
51
Where is cellulose found?
In the cell walls of plants
52
What is the difference between starch/glycogen and cellulose?
Both starch and glycogen are made up of a-glucose molecules and cellulose is made up of b-glucose molecules.
53
What is a dipole? ref. covalent
A covalent bond is formed by the sharing of a pair of electrons. However, the electrons are not shared equally and this causes an unequal distribution of charge known as a dipole.
54
What are polar molecules?
Molecules which have groups with dipoles are polar. They are attracted to water(hydrophilic) and tend to be soluble in water.
55
What are non-polar molecules?
Molecules which do not have dipoles are said to be non-polar and are hydrophobic.
56
What are lipids?
They are all organic molecules which are insoluble in water.
57
What state of matter are fats and oils in at rtp?
Fats are solid at room temperature and oils are liquid at room temperature.
58
What group do all fatty acids contain?
The carboxyl group, -COOH
59
What does unsaturated mean? ref. fatty acids.
Unsaturated means that the molecule does not contain the maximum amount of hydrogen. Unsaturated lipids are those that have double bonds in their hydrocarbon tails.
60
What is monounsaturated and polyunsaturated?
If there is only one double bond, it is monounsaturated. If there is more than one double bond, it it referred to as polyunsaturated.
61
What effect does a double bond have on lipids?
The double bonds make the lipids melt more easily.
62
Describe the saturation of lipids in animals and plants.
In animals, the lipids are saturated and occur as fats. In plants, the lipids are unsaturated and occur as oils.
63
What is glycerol?
It is an alcohol with three hydroxyl groups.
64
What is an ester and an ester bond?
The reaction between an alcohol and an acid produces a chemical known as an ester. The link formed between the acid and alcohol is known as the ester bond/linkage.
65
How is an ester formed and how can it be converted back to its components?
The carboxyl group on the acid reacts with the hydroxyl group on the alcohol to form the ester bond -COO- in the process of condensation and can be converted back to its original acid and alcohol through hydrolysis.
66
What are the most common lipids?
triglycerides
67
What is a glyceride and how is it formed?
A glyceride is an ester formed by the condensation of a fatty acid and the alcohol glycerol.
68
What is a triglyceride and how is it formed?
A triglyceride is an ester formed by the condensation of glycerol which has three hydroxyl groups and three fatty acids. This forms an ester which contains three fatty acid tails and three ester bonds. The tails can vary in length.
69
Describe the solubility of triglycerides in water and other organic solvents.
Triglycerides are insoluble in water due to the non-polarity of the hydrocarbon tails causing it to be hydrophobic. Triglycerides are however soluble in certain organic solvents such as ether, chloroform and ethanol.
70
What are some functions of triglycerides? (4)
1. They are excellent energy reserves due to the large number of C-H bonds as compared to carbohydrates and will therefore release more energy on oxidation than the same mass of a carbohydrate.
2. They act as an insulator against the loss of heat as fat can be stored below the dermis of the skin and around kidneys.
3. It also provides buoyancy.
4. It can be used as a metabolic source of water as it gives CO2 and water on oxidation in respiration.
71
Describe the structure of a phospholipid.
Phospholipids have a hydrophilic phosphate head and two hydrophobic fatty acid tails.
72
What is the function of phospholipids?
They are found in the cell surface membrane with the hydrophilic heads facing outwards and the hydrophobic heads facing inwards forming a membrane that is impermeable to hydrophilic substances.
73
What are proteins made of?
They are made up of amino acids.
74
What are the groups that make up an amino acid and how does each amino acid differ from one another?
An amino acid is made up of an amine group(-NH2), carboxyl group(-COOH), hydrogen atom and an R group. Each amino acid differs from one another due to having different R groups.
75
How is a peptide bond formed?
Two amino acids can join together by forming a bond known as the peptide bond through the removal of water in the process of condensation. The -OH of the carboxyl group reacts with a hydrogen atom from the amine group of the other amino acid, creating a link known as the peptide bond.
76
What is a dipeptide and a polypeptide?
A dipeptide is where a molecule is formed by two amino acids through the process of condensation. A polypeptide is made from many amino acids in a chain linked together by peptide bonds.
77
Are the amine and carboxyl groups basic or acidic?
Amine-basic
| Carboxyl-acidic
78
Describe the function of a ribosome with reference to amino acids.
Ribosomes are the sites where amino acids are joined together to form polypeptides.
79
How many polypeptide molecules can a complete protein molecule contain?
It is variable. It can be one or more.
80
Where does the break down of polypeptides normally happen in the body?
In the stomach and small intestine during digestion where it gets broken down to amino acids in the form of a hydrolysis reaction before getting absorbed into the blood.
81
What is the primary structure? What can a slight change in the primary structure do?
The sequence in which amino acids are joined is known as the primary structure. A slight change in the sequence can affect the protein's structure and function.
82
What is the secondary structure?
The secondary structure is the structure of a protein molecule resulting from the regular coiling and folding of the chain of amino acids.
83
Describe the structure of the a-helix.
The polypeptide chain coils into a regular spiral and is maintained by hydrogen bonds between -NH- group of one amino acid and -CO- group of another amino acid 4 spaces later in the polypeptide chain.
84
Explain the structure of the b-pleated sheet.
In the b-pleated sheet, the chain of amino acids is not tightly coiled and lies in a looser, straighter shape.
85
What causes the folding and coiling of the chain of amino acids?
Hydrogen bonding between the oxygen of -CO- and hydrogen of -NH- group four paces ahead of it as a result of the polar characteristics of the groups.
86
Which two factors can cause a-helix and b-pleated sheet structures to break?
They are easily broken by high temperatures and pH changes.
87
Why do some parts of proteins or proteins show no regular arrangement in the secondary structure?
This is dependent on which R groups are present and therefore what attractions occur between amino acids in a chain.
88
In diagrams of protein structures, how can a-helices, b-pleated sheets and random coils be represented?
a-helices can be represented as coils or cylinders, b-pleated sheets as arrows and random coils as ribbons.
89
What is the tertiary structure?
It is the compact structure of a protein molecule resulting from the three dimensional coiling of the already coiled chain of amino acids. Simply put, it is the way in which a protein coils up to form a precise three-dimensional shape.
90
What are the four types of bond which help to keep folded proteins in their precise shapes?
Hydrogen bonds
Disulphide bonds
Ionic bonds
Weak hydrophobic interactions
91
What are disulfide bonds? What can they be broken down by?
They are strong covalent bonds that form between cysteine molecules(contain sulphur) through oxidation and can be broken down by reducing agents.
92
What are ionic bonds? ref. amino acids. What can they be broken down by?
Ionic bonds form between R groups containing amine and carboxyl groups and can be broken down by pH changes.
93
What are weak hydrophobic interactions with reference to amino acids?
They occur between non-polar R groups due to being repelled by the watery environment around them.
94
What is the quaternary structure?
It is the three dimensional arrangement of two or more polypeptides, or of a polypeptide and a non-protein component in a protein molecule held together by the same four bonds present in the tertiary structure.
95
What are globular proteins? What are some characteristics? Give some examples.
These are proteins which curl up into a spherical shape with their hydrophobic regions pointing to the centre of the molecule and the hydrophilic regions pointing outwards. They are soluble in water. Many have roles in metabolic reactions. Some examples include enzymes and haemoglobin.
96
What are fibrous proteins? What is its role? Give some examples.
hese proteins form long strands and are insoluble in water. They have structural roles. Examples include collagen and keratin.
97
Describe the structure of a haemoglobin molecule.
Each haemoglobin molecule is made up of four polypeptide chains, and so it has a quaternary structure. Each chain is a protein known as globin. Two of the polypeptide chains are a-globin and the other two are b-globin chains. The haemoglobin molecule is nearly spherical with the hydrophobic groups pointing inwards and the hydrophilic groups pointing outwards. Each polypeptide chain of the haemoglobin molecule contains a haem group which in turn contains an iron atom.
98
What is globin and what are the two types?
Globin is a protein and has two types: a-globin and b-globin
99
What is haemoglobin?
It is the oxygen carrying pigment found in red blood cells and is a globular protein.
100
What is a haem group? What is its role in haemoglobin?
It is a prosthetic group as it is a part of a protein molecule but it is not made of amino acids. In haemoglobin, each polypeptide chain has a haem group of which each contain an iron atom. Each iron atom can bind with one oxygen molecule(O2). So, a complete haemoglobin molecule can carry 8 oxygen atoms at a time. It is the haem group that is responsible for the colour of haemoglobin.
101
Explain what causes sickle cell anaemia with reference to the structure of haemoglobin.
In the genetic condition known as sickle cell anaemia, one amino acid which occurs on the hydrophilic surface of the b-globin chain is replaced with a different amino acid. The correct amino acid is glutamic acid which is polar. The substitute is valine, which is non-polar. This makes the haemoglobin molecule much less soluble and causes unpleasant smptoms.
102
What is the colour of haemoglobin when it contains oxygen and when it doesn't?
Oxyhaemoglobin has a bright red colour and is haemoglobin does not contain oxygen it has a purplish colour.
103
What is the most common protein found in animals?
Collagen
104
Describe the structure of collagen.
A collagen molecule is made up of three polypeptide chain which is coiled in the shape of a stretched out helix. The molecule has a compact structure and almost every third amino acid is glycine, which is the smallest amino acid and is found on the inside of the strands. This allows the three strands to lie close together and form a tight coil. The three polypeptide chains are held close together by hydrogen and covalent bonds.
105
What is collagen and where can it be found? What is its role?
Collagen is an insoluble fibrous protein that is found in skin, tendons, cartilage, bones, teeth and walls of blood vessels. It has a structural role.
106
With reference to fibrils and fibres, explain how collagen is held together.
Covalent bonds form cross links between the R groups of amino acids of parallel collagen molecules forming fibrils. Many fibrils lie alongside one another, forming strong bundles known as fibres.
107
What are some characteristics of water?
1. It can be used as a solvent
2. It can be used as a transport medium
3. High specific heat capacity
4. High latent heat of vapourisation
5. High surface tension and cohesion
6. It can be used as a reagent
108
How can water be used as a solvent?
Water is an excellent solvent because of its polarity, hence allowing it to form electrostatic interactions with polar molecules and ions. Non-polar molecules, if surrounded by water are pushed together by the water, since the water molecules are attracted to each other.
109
Give one reason as to why the solvency of water is important.
It acts as the transport medium in the blood in animals and vascular tissues in plants.
110
What is specific heat capacity?
It is the amount of heat required to raise the temperature of 1kg of water by 1 degree celsius.
111
Why does water have a high specific heat capacity?
In order to increase the temperature of water, the hydrogen bonds must be broken to allow free movement. The hydrogen bonds make it more difficult for the molecules which are stuck together by hydrogen bonds to move about freely. It takes a lot of energy to break hydrogen bonds, hence increasing the specific heat capacity of water.
112
Why is the high specific heat capacity of water important?
It makes water more resistant to changes in temperature. Biochemical processes can take place at normal rates and are less likely to be adversely affected by the temperature. Large bodies of water are slow to change temperature, hence providing a stable habitat for aquatic organisms.
113
What is the latent heat of vapourisation?
It is a measure of the amount of heat energy needed to vapourise a liquid.
114
Why does water have a high latent heat of vapourisation?
Water has a high latent heat of vapourisation due to its high specific heat capacity as hydrogen bonds need to be broken before water can be vapourised.
115
Why is LHV important?
The energy transferred to the water molecules to break down the hydrogen bonds results in the loss of energy of the surrounding environment, which therefore cool down.
This is important because it means that living organisms can use evaporation as a cooling mechanism. A large amount of energy can be lost for a small amount of water, reducing the risk of dehydration. This is also important in cooling leaves during transpiration.
116
What is more dense: ice or water?
water
117
Why is density and freezing important with reference to aquatic organisms?
Ice is less dense than water and hence floats on water. This frozen ice insulates the water under it, reducing the tendency for large bodies of water to freeze completely.
118
Describe the cohesion of water and its role.
Water molecules have very high cohesion allowing water molecules to stick to each other allowing water to move in long, unbroken columns in the vascular tissue in plants.
119
Describe the surface tension of water and its role.
The high cohesion results in high surface tension at the surface of water, allowing small organisms to take advantage of the surface of water as a habitat.
120
How is water used as a reagent in plants and animals?
It is used as a reagent in plants during photosynthesis. the energy from sunlight is used to separate the hydrogen from oxygen of water molecules. The hydrogen is then used as a fuel to provide the energy needs of the plant.
During digestion, large molecules are broken down by hydrolysis reactions.
