Chapter 2.2-Biological Molecules Flashcards
(143 cards)
1
Q
What is a condensation reaction?
A
- reaction that occurs when two molecules are joined together with the removal of water
- almost always happens in the same way, when two -OH groups react together
2
Q
What is a hydrolysis reaction?
A
reaction that occurs when a molecule is split into two smaller molecules with the addition of water
3
Q
What type of bonds are broken and formed in condensation and hydrolysis reactions?
A
covalent bonds
4
Q
What is a monomer?
A
a small molecule which binds to many other identical molecules to form a polymer
5
Q
What is a polymer?
A
a large molecule made from many smaller molecules called monomers
6
Q
What is the name of the compound which has two monomers joined together?
A
dimer
7
Q
What is a hydrogen bond?
A
a weak interaction that can occur wherever molecules contain a slightly negatively charged atom, either O-,N- or F-, bonded to a slightly positively charged hydrogen atom
8
Q
Why is water a liquid at room temperature and how does this help living organisms?
A
-hydrogen bonds between water molecules make it more difficult for them to escape to become a gas. It means it has low viscosity, which means it can flow easily
-this enable water to:
provide a habitat 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
9
Q
Why is ice less dense that liquid water and how is this beneficial for living organisms?
A
-in ice stable hydrogen bonds hold molecules far apart and a crystalline structure is formed
-this allows :
aquatic organisms to 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
bodies of water don’t completely freeze up
10
Q
Why is water a good solvent and how does this help living organisms?
A
-water is a polar molecule, the positive and negative parts of the water molecules are attracted to the negative and positive parts of the solute. The water molecule 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
-because water is such 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 dissolved in water
11
Q
How do water molecules demonstrate cohesion and surface tension?
A
- a drop of water does not spread out when it hits a surface, instead it can almost look spherical as hydrogen bonds between the molecules pulls them together.
- the water molecules at the surface of water are all hydrogen bonded to the molecules beneath them, and hence more attracted to the water molecules beneath them than to the air molecules above. This means the surface of the water contracts (water molecules are being pulled inwards), and this gives the surface of the water an ability to resist force applied to it
12
Q
How does surface tension and cohesion of water benefit living organisms?
A
- columns of water in plant vascular tissue are pulled up the xylem tissue together from roots
- insects like pond-skaters can walk on water
13
Q
What is the specific heat capacity of water?
A
- the amount of heat energy required to raise the temperature of water
- 4.2KJ of energy is needed to raise the temperature of 1kg of water by 1 degree
14
Q
Why is the specific heat capacity of water important and how does this benefit living organisms?
A
- water doesn’t heat up or cool down easily
- living things need a stable temperature for enzyme-controlled reactions to happen properly
- aquatic organisms need a stable environment in which to live
15
Q
What is the latent heat of vaporisation and how does this benefit living organisms?
A
- when water evaporates, heat energy, known as the late heat of vaporisation, helps the molecule to break away from each other to become a gas.
- because water is held together by a relatively large number of hydrogen bonds, a relatively large amount of energy is needed for water molecules to evaporate.
- water can help to cool living organisms down and keep their temperature stable. mammals are cooled when sweat evaporates
16
Q
At what temperature is water most dense?
A
4 degrees
17
Q
What elements make up carbohydrates?
A
- carbon
- hydrogen
- oxygen
18
Q
What elements make up lipids?
A
- carbon
- hydrogen
- oxygen
19
Q
What elements make up proteins?
A
- carbon
- hydrogen
- oxygen
- nitrogen
- sulfur
20
Q
What elements make up nucleic acids?
A
- carbon
- hydrogen
- oxygen
- nitrogen
- phosphurus
21
Q
What is the general formula of carbohydrates?
A
CnH2nOn
22
Q
What are the three functions of carbohydrates?
A
- source of energy (glucose)
- store of energy (starch and glycogen)
- structural units (cellulose in plants and chitin in insects)
23
Q
What are monosaccharides?
A
- are the simplest carbohydrates and are the monomers of more complex carbohydrates, and they bond together to form disaccharides or polysaccharides
- they are sugars and particularly important in living things as a source of energy
24
Q
How many carbon atoms do hexose sugars have and give an example of this type of sugar?
A
- six carbon atoms
- glucose (C6 H12 06)
25
How many carbon atoms do pentose sugars have and give an example of this type of sugar?
- five carbon atoms
| - ribose (C5 H10 O5)
26
How many carbon atoms do triose sugars have and give an example of a this type of sugar?
- three carbon atoms
| - glyceraldehyde
27
Are monosaccharides soluble in water?
-yes but are insoluble in non-polar solvents
28
In solution do triose and tetrose sugars exist as a straight chain, ring or cyclic form?
straight chains
29
In solution do pentose and hexose sugars exist as a straight chain, ring or cyclic structure?
ring or cyclic structure
30
What is the difference in structure between alpha-glucose and beta-glucose hexose sugars (C6H1206)?
- in alpha glucose the -OH group is below the plane of the ring
- in beta-glucose the -OH group is above the plane of the ring
31
What is a disaccharide?
This is when two monosaccharides join together
32
What forms when the monosaccharides alpha-glucose and alpha glucose join together?
maltose
33
What forms when the monosaccharides alpha-glucose and fructose join together?
sucrose
34
What forms when the monosaccharides b-galactose and alpha-glucose join together?
lactose
35
What forms when the monosaccharides beta-glucose and beta-glucose join together?
cellobiose
36
What is a glycosidic (covalent) bond?
- a bond formed between two monosaccharides in a condensation reaction
- two hydroxyl groups (-OH) line up next to each other from which a water molecule is removed and which leaves an oxygen atom acting as a link between the two monosaccharide units
37
How can you break a glycosidic bond?
-hydrolysis (addition of water)
38
What disaccharides are reducing sugars?
maltose and lactose
39
What disaccharide are non-reducing sugars?
sucrose
40
What is the molecular formula of ribose?
C5 H10 05
41
What is the molecular formula of deoxyribose?
C5 H10 04
42
What are polysaccharides?
polymers of monosaccharides. They are made of hundreds or thousands of monosaccharide monomers bonded together.
43
Why is glucose a source of energy?
-reactant in respiration which releases energy to make ATP, which is the energy currency of the cell
44
What is the equation for respiration?
Glucose + Oxygen===CO2 +H20 (+ATP)
45
When you join lots of glucose (energy source) molecules together what do they become?
polysaccharide which acts as a store of energy
46
What is starch?
- where plants store their energy
- made up of alpha-glucose molecules bonded together
- found in chloroplasts and in membrane-bound starch grains
- found in two different forms; amylopectin and amylose
47
What is the structure of amylose (in plants)?
- long chain of alpha-glucose molecules
- glycosidic bonds between carbons 1 and 4
- coils into a spiral shape, with hydrogen bonds holding the spiral in place
- hydroxyl groups are located on the inside of the coil on carbon 2, making the molecule less soluble and allowing hydrogen bonds to form to maintain the coils structure
48
What is the structure of amylopectin (in plants)?
- long chain of alpha-glucose molecules
- glycosidic bonds between carbons 1 and 4
- branches formed by glycosidic bonds between carbons 1 and 6
- coils into a spiral shape which is held together by hydrogen bonds. Branches emerge from the spiral
49
What is glycogen?
- where animals store their energy
- found in cells of the muscles and liver
- made up of alpha-glucose
50
What is the structure of glycogen?
- glycosid bonds between carbon 1 and 4, and branches formed by glycosidic bonds between carbons 1 and 6
- 1-4 glycosidic bonds tend to be smaller than in amylopectin, so glycogen has less tendency to coil
- forms more branches than amylopectin, so it is more compact
- easier to remove monomer units as there are more ends
51
Why do glycogen in animals and starch in plants form good stores of energy(monosaccharides)?
- both compact, which means that they do not occupy a large amount of space. They both occur in dense granules within the cell
- 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.
- branched chains (amylopectin and glycogen) are more compact than unbranched chains (amylose), and this means that lots of glucose molecules can be snipped off by hydrolysis at the same time, when lots of energy is required by the cell
- polysacchardies are less soluble in water than monosaccharides.Does not disrupt the water potential of the cell
52
What is the enzyme that hydrolyses the 1-4 glycosidic linkages?
amylase
53
What is the enzyme that hydrolyses the 1-6 glycosidic linkages?
glucosidase
54
What structure can amylose form which makes it very insoluble?
- double helix
- hydrophilic portions of the molecule (-OH) groups are hidden away within the helix
- the hydrophobic regions of the molecule are on the outside of the helix and in contact with the surrounding solution
55
What the carbohydrate polysaccharide which function is to be a structural unit?
cellulose
56
What is cellulose?
- found in plant cell walls (provides mechanical strength and stability to plants)
- it is a homopolysaccharide (made up of one type of monosaccharide; beta-glucose)
57
What are the properties of cellulose?
- strong
- insoluble
- fibrous
58
What is the structure and bonding like in cellulose?
- long chains of beta-glucose molecules (up to 15,000)
- exists as straight chains which lie side by side
- hydrogen and hydroxyl groups are inverted in beta-glucose compared to alpha-glucose. This means that every other beta-glucose molecule in the chain is rotated by 180 degrees
- beta 1-4 glycosidic bonds
- there are hydrogen bonds between the rotated beta-glucose molecule in each chain gives the chain additional strength and stops it spiralling
- hydroxyl group on carbon 2 sticks out so hydrogen bonds can be made between the rotated beta-glucose molecule in different chains
59
When 60/70 cellulose chains are bound together what is formed?
- microfibrils, which are 10-30 nm in diameter
- these then bundle together into macrofibrils containing up to 400 microfibrils
- macrofibrils run in all directions criss-crossing the wall for extra strength
60
Why is the structure of cellulose allow it to be an excellent material for plant cell walls?
- microfibrils and macrofibrisl have very high tensile strength, both because of the strength of the glycosidic bonds but also because of the hydrogen bonds between chains. As plants do not have a rigid skeleton, each cell needs to have strength to support the whole plant.
- macrofibrils run in all directions, criss-crossing the wall for extra strength. This prevents plant cells from bursting when they are turgid.
- cellulose is difficult to digest cellulose because of the glycosidic bonds are hard to break. most animals do not even have an enzyme to catalyse the reaction
- there is space between the macrofibrils for water and mineral ions to pass on their way into and out of the cell. This makes the cell wall fully permeable
61
What substances can be added to the macrofibril structure of cellulose to make it waterproof?
-cutin and Suberin are waxes that block the spaces in the cell wall
62
What are the two other structural polysaccharides?
- bacteria cell walls are made from peptidoglycan, which is made from long polysaccharide chains that lie in parallel, cross-linked by short peptide chains
- exoskeletons:insect and crustacean exoskeletons are made of chitin. It differs from cellulose as it has an acetyamino group (NH.0CCH3) rather than a hydroxyl group on carbon 2. Forms cross-links between long parallel chains of acetylglucosamine, in a similar way to cellulose.
63
What are lipids?
a group of substances that are soluble in alcohol rather than water. They include triglycerides, phospholipids, glycolipids and cholesterol
64
What is a macromolecule?
a very large, organic molecule such as a lipid
65
Are lipids soluble in water?
-no because they are not polar so do not attract water molecules but can dissolve in alcohol
66
What is a triglyceride?
- lipid which is made up of glycerol and fatty acids
| - one glycerol molecule is bonded to 3 fatty acids.
67
What is glycerol?
- 3 carbon molecule with 3 -OH groups
| - molecular formular = C3 H8 03
68
What is a fatty acid?
-have a carboxyl group (-COOH) at one end, attached to a hydrocarbon tail, made of only carbon and hydrogen atoms. (may be anything from 2 to 20 carbons long)
69
What does it mean when a fatty acid is saturated?
there are no C=C bonds in the molecule (double bonds)
70
What does it mean when a fatty acid is unsaturated?
there is a double bond (C=C) between two of the carbon atoms
71
What is a monounsaturated fatty acid and give an example?
- there is one C=C double bond
| - e.g. oleic acid
72
What is a polyunsaturated fatty acid and give an example?
linoleic acid
73
How do unsaturated fatty acids affect the structure and function of fatty acids?
- C=C bond gives it a kink where the double bond is. These kinks push the molecules apart slightly, it makes them more fluid.
- animal lipids contain lots of saturated fatty acids, which are often solid at 20 degrees. If there are more unsaturated fatty acids, the melting point is lower.
74
What is the name of the bond that forms between glycerol and fatty acids and what type of reaction is it?
- a condensation reaction happens between the -COOH group of the fatty acid and the three -OH groups on the glycerol.
- covalent bond formed is known as an ESTER BOND
75
What is esterification?
type of condensation reaction that occurs between glycerol and fatty acids to make a ester bond
76
How are triglycerides used as energy sources and energy stores?
- energy store: they can be broken down in respiration to release energy and generate ATP. The first step is to hydrolyse the ester bonds, and then glycerol and the fatty acids can be broken down completely to water and C02.
- Energy store: as they aren't soluble in water, they can be stored without affecting the water potential of the cell.
77
What are the other functions of triglycerides apart from being good energy sources and stores?
- insulation: fat is used as insulation; adipose tissue is a storage location for lipid in whales (blubber), acting as a heat insulator
- Buoyancy: because fat is less dense than water, it is used by aquatic mammals to help them afloat.
- Protection: humans have fat around delicate organs, such as their kidneys to act as a shock absorber.
78
What is a phospholipid?
same structure as triglycerides, except one of the fatty acids is replaced by a phosphate group (H3PO4)
79
What does it mean when a molecule is amphiphatic and how does this relate to phospholipids?
- this is when a molecule has both hydrophilic and hydrophobic elements
- phospholipids are amphiphatic because they have a hydrophilic 'head' which is the phosphate group which is polar and can interact with water, and also a hydrophobic 'tail' which is the fatty acid portion of the phospholipid which isn't polar and can't interact with water
80
What is a micelle?
tiny balls with the tails tucked away inside, and the heads pointing out outwards into the water
81
What is the phospholipid bilayer and what is its function?
- inside and outside a cell membrane is an aqueous solution. The phospholipids form a bilayer, with two rows of phospholipids, tails pointing inwards and heads pointing outwards into the solution.
- 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.
- the membrane is selectively permeable. Only small and non-polar molecules are able to move through the tails in the bilayer, such as oxygen and carbon dioxide. Therefore it regulates what can come into and out of the cell
82
What is cholesterol?
- steroid alcohol which is a type of lipid which is not made from glycerol or fatty acids.
- consists of four carbon based rings or isoprene units. it has a single -OH group at one end of the molecule and a hydrocarbon chain at the other end
- it is a small and hydrophobic molecule so can sit in the hydrophobic part of the bilayer.
83
Where is cholesterol made in the body and whats its function?
- mainly made in the liver
| - regulates the fluidity of the membrane, preventing it from becoming too fluid or stiff
84
What hormones can be made from cholesterol?
- testosterone
- oestrogen
- vitamin D
85
What is the name of the cholesterol derivative in plants and how does it differ from cholesterol in humans?
- stigmasterol
| - double bond between carbon 22 and carbon 23
86
What is the name of the core of a glycogen or amylopectin molecule that is resistant to hydrolysis by enzymes?
limit dextrin
87
What is an amino acid?
monomers of all proteins, and all amino acids have the same basic structure
88
What is a protein?
large polymers comprised of long chains of amino acids/
89
What is the structure of a amino acid?
- each amino acid contains an amino group (-NH2) at one end, and a carboxyl group (-COOH) group at the other end.
- central carbon atom bonded to a hydrogen and also a R group (depends on the certain amino acid)
90
How is an amino acid amphoteric?
- it has basic and acidic properties
- NH2 group can accept a H+ and become NH3+, therefore accepting a H+ ION
- COOH group can release a H+ ion and become -COO-
91
What is a peptide bond?
a bond formed when two amino acids are joined by a condensation reaction
92
What is the name of the enzyme that breaks down peptide bonds?
protease enzymes in the intestine
93
What is the primary structure of a protein?
the sequence of amino acids found in a molecule
94
What are the maximum number of ways in which amino acids can be ordered?
20^100
95
What is the secondary structure of an amino acid?
the coiling or folding of an amino acid, which arises often as a result of hydrogen bond formation between different parts of the chain. The main forms of secondary structure are the helix and the pleated sheet
96
What is a polypeptide?
chain of amino acids
97
What is a dipeptide?
two amino acids joined together
98
What is a the alpha helix?
- 36 amino acids per 10 turns of the helix
- secondary protein structure
- right-handed spiral configuration
- the helix is held together by hydrogen bonds between the -NH2 group of one amino acid and the -CO group of another four places ahead of time
99
What are beta-pleated sheet?
- zig-zag structure
- hydrogen bonds between the -NH group of one amino acid and the -CO group go another further down the strand hold the sheets together
100
What is the tertiary structure of a protein?
the overall three-dimensional shape of a protein molecule. Its shape arises due to interactions including hydrogen bonding, disulphide bridges, ionic bonds and hydrophobic interactions
101
What are the two different shapes that can form from the tertiary structure?
- supercoiled shape (e.g. fibrous proteins)
| - spherical shape (e.g. globular proteins)
102
What is the quaternary structure of a protein?
protein structure where a protein consists of more than one polypeptide chain. For example, insulin has a quaternary structure
103
How does ionic bonding arise in polypeptides?
- form between those carboxyl and amino groups that are part of the R groups
- NH3+ and COO- groups attract each other when they are ionised
104
What are disulfide links?
the R group of the amino acid cysteine contains sulphur. disulfide bridges are formed between the R groups of two cysteine. These are strong covalent bonds
105
What are hydrophobic and hydrophilic interactions?
hydrophobic parts of the R groups tend to associate together in the centre of the polypeptide to avoid water. In the same way, hydrophobic parts are found at the edge of the polypeptide to be close to water. These interactions cause twisting of the amino acid chain, which changes the shape of the protein
106
What is a fibrous protein?
has relatively long, thin structure, is insoluble in water and metabolically inactive, often having a structural role within an organism
107
What is a globular protein?
- has molecules of a relatively spherical shape, which are soluble in water, and often have metabolic roles within the organism
- has regular, repetitive sequences of amino acids
108
What is the quaternary structure of haemoglobin?
- four polypeptides: two alpha-globing chains and 2 beta-globing chains
- at one position on the outside of each chain, there is a space in which a ham group is held. Groups like this are called prosthetic groups. The harm group contains a Fe ion
109
How does haemoglobin carry out its function?
- globular protein
- its function is to carry oxygen from the lungs to the tissues
- in the lungs, an oxygen molecule binds to the iron in each of the four ham groups in the haemoglobin molecule.
- when it binds, haemoglobin turns from a purple red colour to bright red
110
What is the structure and function of insulin?
- made of two polypeptide chains.
- the A chain begins with a section of alpha-helix, and the B chain ends with a section of beta-pleated sheets.
- it is soluble in water
- binds to glycoproteins receptors on the outside of muscle and fat cells to increase their uptake of glucose from the blood, and to increase their rate of consumption of glucose.
111
What is the structure and function of pepsin?
- enzyme that digests protein in the stomach
- made up of a single polypeptide chain of 327 amino acids, but it folds into a symmetrical tertiary structure.
- mostly has acidic R groups as the stomachs environment is very acidic
112
What is the function of collagen?
- fibrous protein
- provides mechanical strength
- collagen in artery walls prevents the artery bursting when withstanding high pressure from blood being pumped by the heart.
- tendons are made of collagen and connect muscles to bones, allowing them to pull on bones
- cartilage nad connective tissue are made from collagen
113
What is the function of keratin?
- fibrous protein
- provides mechanical strength
- mostly made up of the amino acid cysteine, so a lot of disulfide links can be made which are very strong
- keratin is found in body parts that need to be hard and strong, such as nails, hoofs,horns,scales,fur and feathers.
- waterproof and provides an impermeable barrier to infection.
114
What is the function of elastin?
- cross linking and coiling make the structure of elastin strong and extensible.
- found in living things where they need to stretch or adapt their shape as part of life processes.
- elastin is found in our skin and allows skin to stretch around our bones and muscles
- also found in blood vessels and helps them stretch and recoil as blood is pumped through them, helping maintain the pressure of the blood
115
What is a conjugate protein?
a protein which is associated with a prosthetic group
116
What is Ab initio protein modelling?
- 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 the other methods sometimes need applying to reduce the number of solutions
117
What is the Comparative protein modelling technique?
- scans the amino acid sequence against a database of solved structures and produces a set of possible models which would match that sequence.
- this is known as protein threading
118
Why are Ca^2+ cations important in biological processes?
- increases the rigidity of various structures such as bone, teeth, cartilage and exoskeletons
- important in clotting blood and muscle contractions (stimulates muscle contraction and regulates transmission of nerve impulses)
- regulates the permeability of cell membranes
- cell wall development in plants, and formation of middle lamella between cell walls
119
Why are Na^+ cations important in biological processes?
- involved in regulation of osmotic pressure, control of water levels in body fluid and maintenance of pH
- affects the absorption of carbohydrates in the intestine, and water in the kidney
- contributes to nervous transmission and muscle contraction
- Constituent of a vacuole in plants which helps maintain turgidity
120
Why are K^+ cations important 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 proteins, 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
121
Why are H^+ cations important in biological processes?
- involved in photosynthesis and respiration
- involved in transport of oxygen and carbon dioxide in the blood
- involved in regulation of blood pH
122
Why are NH4^+ cations important in biological processes?
- 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.
- component of the nitrogen cycle
123
Why are NO3^- anions important in biological processes?
- component of amino acids, proteins, vitamins and chlorophyll
- essential component of nucleic acids
- some hormones are made of proteins, which contain nitrogen, e.g. insulin
- component of the nitrogen cycle
124
Why are HCO3^- anions important in biological processes?
- involved in regulation of blood pH
| - involved in transport of carbon dioxide in and out of the blood
125
Why are Cl^- anions important in biological processes?
- helps in the production of urine in the kidneys, 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 HCL in the stomach
126
Why are PO4^3- anions important in biological processes?
- increases rigidity of bone, teeth nad cartilage and is a component of the exoskeleton of crustaceans
- component of phospholipids, ATP, nucleic acids and several enzymes
- involved in regulation of blood pH
- helps root growth in plants
127
Why are OH^- anions important in biological processes?
-involved in regulation of blood pH
128
How do you test for starch?
- Add iodine solution (in potassium iodide) to a sample.
| - if starch is present, you will see a colour change of yellow-brown to blue-black
129
How do you test for reducing sugars?
- all monosaccharides and some disaccharides are reducing sugars
- heat the reusing sugar with Benedictus solution (alkaline copper(II) sulfate)
- if reducing sugar is present there will be a colour change from blue to green to yellow to orange-red
- benedicts solution contains Cu ^2+ ions Whig are reduced to Cu+ ions, forming a 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
130
How can u measure the concentration of the sugar using benedicts?
Use Benedict’s in excess, the intensity of the red colour is proportional to the concentration of the sugar
131
How do you test for non-reducing sugars?
- hydrolyse the bond first, to 'free up' these 'reducing groups', and then test for reducing sugars
- test a sample for reducing sugars to check there are none there in the first place
- take a separate sample and boil it with HCL to hydrolyse the sucrose into glucose and fructose
- cool the solution and use sodium hydrogen carbonate solution to neutralise it.
- test for reducing sugars again; a positive result indicates that non -reducing sugar(sucrose) is present
132
How do you tests for lipids?
- carry out the emulsion test
- take a sample and mix it thoroughly with ethanol. Any lipid will go into solution in the ethanol. (lipids are not soluble in water)
- filter
- pour the solution with water in a clean test tube
- a cloudy white emulsion test indicates the presence of lipids. This is made up of tiny lipid droplets that come out of solution when mixed with water
133
How do you test for proteins?
-biuret test
-add sodium hydroxide into the spotting tile containing the food and then add copper sulfate.
- if a protein is present there will be a colour change from light blue to lilac
-
134
What is calorimetry?
technique to find out the concentration of sugar in the original sample
135
How do you carry out a colorimeter test on a sugar?
1. use a centrifuge to separate the precipitate and any excess Benedict's solution
2. using a pipette, take a sample of the Benedict's solution without the precipitate and add this to a cuvette, which is placed inside the colorimeter
3. place a red filter over the cuvette, and then shine red light through the solution, and detect how much light (percentage transmission). The solution reflects blue light and absorbs red light.
4. light that is transmitted hits a photo-electric cell which is connected to a display.
136
How do you create a calibration curve?
1. Take a series of known concentrations of reducing sugar
2. using a sample of each, carry out Benedict's test
3. Use a colorimeter to record the percentage transmission of light through each Benedict's solution.
4. Plot a graph to show 'transmission of light' against the concentration of reducing sugar
137
What is a biosensor
-they take a biological or chemical variable which cannot be easily measured, and convert it to an electrical signal
138
What are the steps in using a biosensor?
1. molecule to be measured binds to the receptor on a biological layer. This is known as the binding event
2. the transducers surface takes the electrical signal and passes it onto a single conditioner
139
What is thin layer chromatography?
used to separate mixtures of substances into their components
140
What is the stationary phase?
either the chromatography paper or a thin-layer chromatography (TLC) plate.
141
What is the mobile phase?
- solvent for the biological molecules, for example 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
142
How do you find out the Rf value in thin-layer chromatography?
- Rf=x/y
- x= distance from the pencil line to the centre of a spot of pigment
- y= distance from the pencil line to the solvent front
143
What molecules travel fast up the paper, and what molecules travel slowly up the paper?
- the TLC plate has exposed -OH groups which can lead to the pigment forming hydrogen bonds, alongside other dipole interactions. A highly polar solute will tend to stick to the surface (it is absorbed), and hence move more slowly up the plate
- non-polar solutes move much quicker up the TLC plate
