1. Biological Molecules Flashcards
1
Q
Define ‘covalent bonding’
A
Atoms share a pair of electrons in their outer shells, resulting in the outer shells of both electrons being filled, forming a stable molecule.
2
Q
Define ‘ionic bonding’
A
Ions with opposite charges attract one another, causing a transfer of electrons, forming an ionic bond by electrostatic attraction.
3
Q
Define ‘hydrogen bonding’
A
The electrons are polarised. The negative region and positive region of the polarised molecule attract each other, forming a weak electrostatic bond between the two.
4
Q
Define ‘monomer’
A
One of many small molecules that combine collectively to form a larger one known as a ‘polymer’.
5
Q
Define ‘polymer’
A
Large molecules made up of repeating smaller molecules/monomers.
6
Q
Define ‘polymerisation’
A
Process by which polymers are formed.
7
Q
Describe the process of a condensation reaction
A
Chemical process in which 2 molecules combine to form a more complex one with the elimination of a simple substance, usually water.
8
Q
Describe the process of hydrolysis
A
The breaking down of large molecules into smaller ones by the addition of water molecules.
9
Q
Define metabolism
A
All the chemical processes that take place collectively in an organism
10
Q
What is a single carbohydrate monomer called?
A
Monosaccharide
11
Q
What is a pair of monosaccharides called?
A
Disaccharide
12
Q
What are many monosaccharides called?
A
Polysaccharide
13
Q
What is the general formula of monosaccharides?
A
(CH2O)n
14
Q
What is the name of the test for reducing sugars?
A
Benedit’s test
15
Q
Describe the Benedict’s test for reducing sugars?
A
-Add 2cm^3 of the food sample to be tested to a test tube. If the sample is not already in liquid, first grind it up in water.
-Add an equal vol of Benedict’s reagent.
-Heat the mixture in a gently boiling water bath for 5 mins.
If reducing sugar is present, solution turns orange-brown.
16
Q
Which monosaccharides make up the disaccharide maltose?
A
Glucose & glucose
17
Q
Which monosaccharides make up the disaccharide sucrose?
A
Glucose & fructose
18
Q
Which monosaccharides make up the disaccharide lactose?
A
Glucose & galactose
19
Q
What is the bond formed between 2 monosaccharides?
A
Glycosidic bond
20
Q
What is the test for non-reducing sugars?
A
Benedict’s test
21
Q
Describe the Benedict’s test for non-reducing sugars
A
- If food sample isn’t already liquid, it should be ground.
- Add 2cm^3 of the food sample to 2cm^3 of dilute hydrochloric acid in a test tube and place in a gently boiling water bath for 5 mins. The dilute hydrochloric acid will hydrolyse any disaccharide present into its constituent monosaccharides.
- Slowly add sodium hydrogencarbonate solution to the test tube in order to neutralise the hydrochloric acid. Test with pH paper that the solution is alkaline.
- Heat the resulting solution with 2cm^3 Benedict’s reagent in a water bath for 5 mins.
- If non-reducing sugar present, the Benedict’s solution will turn orange-brown.
22
Q
Describe the test for starch
A
- Place 2cm^3 of the sample to a test tube.
- Add 2 drops of iodine solution and shake.
- Starch will turn solution blue-black.
23
Q
What is starch made up of?
A
Chains of alpha-glucose monosaccharides linked by glycosidic bonds formed in condensation reactions.
24
Q
What is the function of starch?
A
Energy storage in plants
25
How is the structure of starch adapted to its function?
- Insoluble, doesn't affect water potential so water is not drawn into cells by osmosis.
- Large and insoluble, doesn't diffuse out of cells.
- Compact, a lot stored in a small place.
- Hydrolysis produces alpha-glucose, easily transported and used in respiration.
- Branched, has many ends, enzymes can act simultaneously and release glucose monomers.
26
What is glycogen made up of?
Chains of alpha-glucose monosaccharides linked by glycosidic bonds formed in condensation reactions.
27
What is the main function of glycogen?
The main carbohydrate storage product of animals. Stored as granules in liver/muscles.
28
How is the structure of glycogen related to its function?
- Insoluble, doesn't affect water potential so water is not drawn into cells by osmosis.
- Large and insoluble, doesn't diffuse out of cells.
- Compact, a lot stored in a small place.
- Highly branched, enzymes can act simultaneously to form glucose- used in respiration, animals have a higher metabolic rate than plants.
29
What is cellulose made up of?
Made of monomers of beta-glucose, which form straight, unbranched chains.
30
What is the main function of cellulose?
Provides rigidity to plant cell- prevents cell from bursting as water enters by osmosis. Cellulose exerts an inward pressure, preventing any further influx of water. Makes plant cells turgid, pushing against one another, important in maintaining rigidity of stems/leaves, maximising area for photosynthesis.
31
How is the structure of cellulose related to its function of providing support and rigidity?
- Cellulose made of beta-glucose and form long, unbranched chains.
- These cellulose molecular chains run parallel to each other, cross linked by hydrogen bonds to add collective strength.
- Cellulose molecules grouped together to form microfibrils, which in turn are grouped to form fibres, all of which providing more strength.
32
What are the two main groups of lipids?
Triglycerides and phospholipids
33
What are some lipid functions?
- Contribute to flexibility of membranes and transport of lipid soluble substances across them.
- Source of energy
- Waterproofing
- Insulation
- Protection
34
What are the products of hydrolysis of a triglyceride?
Glycerol and three fatty acids
35
What variation results in lipids having different properties?
Variation in fatty acids, all glycerol molecules in fatty acids are the same. There are over 70 different fatty acids, all with a carboxyll group with a hydrocarbon chain attached.
36
What does it mean if a fatty acid is 'saturated'?
All the carbon atoms are linked with the maximum number of hydrogen atoms.
37
What does it mean if a fatty acid is 'mono-unsaturated'?
There's one single carbon double bond present.
38
What does it mean if a fatty acid is 'poly-unsaturated'?
There's more than one carbon double bond present.
39
How does the structure of triglycerides relate to their properties?
- They have a high ratio of energy-storing carbon-hydrogen bonds to carbon atoms, making an excellent source of energy.
- Have a low mass to energy ratio- so good storage molecules, energy can be carried in a small volume.
- Large, non-polar molecules so insoluble in water, so storage doesn't affect osmosis/water potential in cells.
- Have a high ratio of hydrogen to carbon atoms so release water when oxidised, providing an efficient source of water.
40
What are phospholipids made up of?
Glycerol, 2 fatty acids and a phosphate group.
41
What is hydrophilic head of the phospholipid, and what substance does it interact with?
The phosphate molecule interacts with water (is attracted), but not with fat.
42
What is hydrophobic tail of the phospholipid, and what substance does it interact with?
The fatty acid molecules interacts and mixes readily with fat, but orients away from water.
43
How is the structure of phospholipids related to their properties?
- They're polar molecules, the hydrophilic head and hydrophobic tail enables them to form a bilayer within cell membranes, therefore in aqueous environments, a hydrophobic barrier forms surrounding the cell.
- The hydrophilic phosphate heads of the phospholipid molecules help to hold at the surface of the cell membrane.
- The phospholipid structure allows them to form glycolipids by combing with carbohydrates within the cell membrane. Glycolipids important in cell recognition
44
What is the name of the test for lipids?
The Emulsion test
45
Describe the test for lipids
1. Take a dry and grease free test tube.
2. To 2cm^3 of the sample being tested, add 5cm^3 of ethanol.
3. Shake the tube thoroughly to dissolve any lipid in the sample.
4. Add 5cm^3 of water and shake gently.
5. A cloudy-white colour indicated lipid present.
6. To control, repeat the experiment using water instead of the sample: the final solution should remain clear.
46
List 2 differences between a triglyceride and phospolipid molecule
Triglyceride has 3 fatty acids, phospholipid has 2.
| Triglycerides are nonpolar, phospholipids are polar.
47
Organisms that move, eg animals, use lipids rather than carbohydrates as an energy store. Suggest one reason why.
Lipids provide more than twice the energy as carbohydrate when oxidised. If far is stored, the same amount of energy can be stored for less than half the mass. Therefore it is a lighter storage produce- an advantage to a mobile organism.
48
What are the 4 chemical groups that make up an amino acid
- Amino group (-NH2) a basic group.
- Carboxyl group (-COOH) an acidic group
- Hydrogen atom (-H)
- R group- a variety of different chemical groups, each amino acid has a different R group
49
What is the bond linking amino acids in proteins called?
Peptide bond
50
Describe the formation of a peptide bond
Condensation reaction- water is removed, by combining the -OH from the carboxyll group of one amino acid and the -H from the amino group of another amino acid. A peptide bond is formed between the carbon of one amino acid and the nitrogen of another.
51
Describe the primary structure of proteins
The primary structure is the sequence of amino acids in a polypeptide chain. The primary structure determines the shape and function of a protein. A change in just one amino acid will affect the proteins function.
52
What determines the amino acid sequence?
DNA. Polypeptides have many of the natural 20 amino acids joined in sequences, there's almost a limitless amount of primary protein structure.
53
Describe the secondary structure of protein
The hydrogen of the -NH group has a positive charge, while the -O on the -C=O group has an overall negative charge. Therefore they readily form weak hydrogen bonds, causing the long polypeptide chain to twist into the alpha--helix shape.
54
Describe the tertiary structure of protein
The alpha-helices are twisted and folded to form a complex, specific 3D structure, which determines the proteins function. The 3D structure is maintained by:
-Disulfide bridges- strong
-Ionic bonds-formed between carboxyl and amino groups not involved in peptide bonds. Easily broken by pH change.
-Hydrogen bonds- numerous but easily broken.
(Position of these bonds depends on primary structure)
55
Describe the quaternary structure of protein
Large proteins form complex molecules, often associated with non-protein/prosthetic groups.
56
Name the test for proteins
Biuret test
57
Describe the test for proteins
1. Place a sample of the solution to be tested in a test tube and add an equal volume of sodium hydroxide solution at room temp.
2. Add a few drops of dilute (0.05%) copper (II) sulfate solution and mix gently.
3. A purple coloration indicates the presence of peptide bonds, hence a protein. If no protein is present, solution remains blue.
58
Do enzymes increase or decrease the activation energy of a reaction?
Enzymes decrease the activation energy, allowing reactions to take place at a lower temperature.
59
What type of protein is an enzyme?
Globular protein
60
Describe the functional region of enzymes
The active site- made up of a small number of amino acids.
61
What do enzymes form when they fit into a substrate?
An enzyme-substrate complex.
62
What theory does the 'Induced fit model' of enzyme action propose?
That the active site forms as the enzyme and substrate interact. The proximity (environmental change) of the enzyme, causes a change in the enzyme that forms the functional active site.
63
Define 'catalyst'
A substance that alters the rate of a chemical reaction without undergoing a permanent change.
64
Explain why enzymes are effective in tiny quantities.
They are not used up in the reaction so can be used repeatedly- they're biological catalysts.
65
Outline why changing one of the amino acids that make up the active site could prevent the enzyme from functioning
The changed amino acid may no longer bind to the substrate, which will then not be positioned correctly, if at all, in the active site.
66
Explain why changing certain amino acids that are not part of the active site also prevents the enzyme from functioning
The changed amino acid may be one that forms hydrogen bonds with other amino acids. If the new amino acid doesn't form hydrogen bonds, the tertiary structure of the enzyme will change, including the active site, so that the substrate may not fit.
67
What's the effect of temperature on enzyme action?
A rise in temperature increases the kinetic energy of molecules, causing them to move around rapidly and collide more often, forming more enzyme-substrate complexes; faster rate of reaction.
68
Describe denaturation.
As the temperature rises beyond the optimum, the hydrogen bonds and other bonds in the enzyme begin to break. This results in the enzyme, including the active site to change shape. At first, the substrate fits less easily into the active site, slowing the reaction. Denaturation is the point where the enzyme is so disrupted that it stops working completely. It is a permanent change, and that enzyme can't function again.
69
What's the effect of pH on enzyme action?
Each enzyme has an optimum pH. An increase or decrease in pH reduces the rate of enzyme action. If the change in pH is more extreme than its optimum, the enzyme becomes denatured. This is because a change in pH alters the charges on amino acids that make up the active site of an enzyme, so the enzyme-substrate complexes can't form. If the pH change is significant, the bonds maintaining the enzyme's tertiary structure may break. The active site then changes shape.
70
What does the 'pH' of a solution mean?
The measure of a solution's hydrogen ion concentration.
71
What is the effect of enzyme concentration on the rate of enzyme action?
Low enzyme conc= There are too few enzyme molecules to allow all substrate molecules to find an active site at one time. The rate of the reaction is therefore only half the max possible for all the substrate available.
Intermediate enzyme conc= All the substrate molecules can occupy an active site at the same time. Rate of reaction at its max- all active sites full.
High enzyme conc= Addition of further enzyme molecules has no effect, there's already enough active sites to accommodate all the available substrate. No increase in rate of reaction.
72
What's the effect of substrate concentration on the rate of enzyme action?
Low substrate conc= Too few substrate molecules to occupy all available active site. Rate of reaction only half of max.
Intermediate substrate conc= All active sites occupied at one time. The rate of reaction at max, all active sites full.
High substrate conc= Addition of further substrate molecules has no effect, as all active sites are already occupied at one tine, no increase in rate of reaction.
73
Calculate the pH of a solution with a hydrogen ion concentration of 0.0001 M
0.0001 M = 1 x 10-4
| =pH 4
74
What are enzyme inhibitors?
Substances that directly or indirectly interfere with the functioning of the active site of an enzyme, and so reduce its activity.
75
Name the 2 different types of enzyme inhibitors?
- Competitive inhibitor- binds to active site of enzyme.
| - Non-competitive inhibitor-binds to enzyme at a position other than the active site.
76
How do competitive inhibitors reduce enzyme activity?
Competitive inhibitors have a molecular shape similar to a substrate, allowing them to occupy the active site of an enzyme, leading them to compete with substrate. The difference between concentration of the inhibitor and the substrate which determines its effect on enzyme activity. The inhibitor is not permanently bound to the active site, and so when it leaves, another molecules takes its place. Could be a substrate or inhibitor, depending on the concentration of each. All the substrate molecules will eventually fill each active site, but if the inhibitor concentration is increased, this will take longer.
77
If substrate concertation is increased, what is the effect of the inhibitor on enzyme action?
The effect of the inhibitor is reduced.
78
How do non-competitive inhibitors reduce enzyme activity?
Non-competitive inhibitors attach themselves to the enzyme at a binding site which isn't the active site. When attached, the inhibitor alters the shape of the enzyme and thus its active site so substrate molecules can no longer occupy it it, and so the enzyme cannot function. The substrate and inhibitor are not competing for the active site, so the increase in substrate concentration doesn't decrease the effect of the inhibitor.
79
Distinguish between a competitive and non-competitive inhibitor
Competitive inhibitors occupy the active site of an enzyme, while non-competitive inhibitor attach to the enzyme at a site other than the active site.
80
An enzyme-controlled reaction is inhibited by Substance X. Suggest a simple way in which you could tell whether Substance X is a competitive or non-competitive inhibitor.
Increase the substrate concentration. If the degree of inhibition is reduced, it's a competitive inhibitor. If it stays the same, it's a non-competitive inhibitor.
