Unit 2.1 Biological Molecules Flashcards
(167 cards)
1
Q
What is the role of carbohydrates?
A
Energy storage and supply, structure (in some organisms)
2
Q
What is the role of proteins?
A
Structure, transport, enzymes, antibodies, most hormones
3
Q
What is the role of lipids?
A
Membranes, energy supply, thermal insulation, protective layers/padding, electrical insulation in neurones, some hormones
4
Q
What is the role of vitamins and minerals?
A
Form parts of some larger molecules and take part in some metabolic reactions, some act as coenzymes or enzyme activators
5
Q
What is the role of nucleic acid?
A
Information molecules, carry instructions for life
6
Q
What is the role of water in organisms?
A
Takes part in many reactions, support in plants, solvent/medium for most metabolic reactions, transport
7
Q
Define metabolism
A
The sum total of all the biochemical reactions taking place in the cells of an organism
8
Q
What chemical elements are found in biological molecules?
A
Carbon, hydrogen, oxygen and nitrogen (mostly)
9
Q
What is a catabolic reaction?
A
A reaction that breaks larger molecules into smaller molecules
10
Q
What is an anabolic reaction?
A
A reaction that involves building smaller molecules into larger ones
11
Q
How can a carbon atom be made stable?
A
By forming 4 covalent bonds with other atoms, forming a molecule
Can form chains or rings
12
Q
What is a monomer?
A
A small molecule that is one of the units bonded together to form a polymer
13
Q
What is a polymer?
A
A large molecule made up of many repeating smaller molecules (monomers) covalently bonded together
14
Q
What happens in a condensation reaction?
A
A water molecule is released; a new covalent bond is formed; a larger molecule is formed by the bonding of smaller molecules
15
Q
What happens in a hydrolysis reaction?
A
A water molecule is used; a covalent bond is broken; smaller molecules are formed by the splitting of a larger molecule
16
Q
How do hydrogen bonds form?
A
When a slightly negative charged part of a molecule comes close to a slightly positively charged hydrogen atom in the same (or another) molecule
17
Q
What is the general formula for a carbohydrate?
A
Cn(H2O)n
18
Q
What are the functions of carbohydrates in organisms?
A
Energy source, energy store, structure
19
Q
What are the properties of monosaccharides?
A
Soluble in water; sweet tasting; form crystals; tend to occur in ring structures
20
Q
Draw the structure of the 2 types of ring-form glucose.
A
a-glucose: 5 carbon ring (CH2OH branched from carbon 5)
The OH at carbon 1 is below the plane of the ring
(below the H)
ß-glucose: 5 carbon ring (CH2OH branched from carbon 5)
The OH at carbon 1 is ABOVE the plane of the ring
(above the H)
21
Q
What type of bond joins 2 monosaccharides together and what type of molecule does it form? How does the bond form?
A
A type of covalent bond - glycosidic bond. Forms a disaccharide molecule and a water molecule. Condensation reaction.
22
Q
Which type of glucose is used for respiration? Why?
A
a-glucose. Animals and plants have enzymes that can break a-glucose down, but because of the different arrangement of H and OH at carbon 1, ß-glucose cannot be broken down. (enzyme function is based on shape; a and ß glucose are shaped differently)
23
Q
How is amylose formed?
A
2 a-molecules join together in a condensation reaction to form maltose. This reaction can be repeated lots to form amylose. The glycosidic bond is between carbon-1 of one molecule and carbon-4 of the next (1,4 glycosidic bond)
24
Q
Name 2 properties of amylose
A
The long chains coil into a spring because of the shape of the glucose molecules.
Not water soluble
25
What is starch made from?
Long, straight-chain molecules and branched amylopectin.
26
What is glycogen made from, and how does it differ from starch?
Large, branched molecule made up of a-glucose subunits (like starch). Glycogen is more compact than starch: the 1-4 linked glucose chains in glycogen tend to be shorter than in amylopectin and have many more branches extending from the chain
27
What shape do a-glucose molecules form when bonded together?
Coiled, spring-like chains.
28
What shape do ß-glucose molecules form when joined together?
Long, straight chain
29
What are cellulose chains?
ß-glucose polymer chains
30
How are cellulose fibres arranged to form plant cell walls?
About 60-70 cellulose molecules become cross-linked by hydrogen bonds to form larger bundles called microfibrils. These are held together by more hydrogen bonds to form larger molecules called macrofibrils, which have great mechanical strength. They are embedded in pectins to form cell walls
31
What is the function of the plant cell wall?
Gives strength to each cell, supporting the whole plant.
32
How is the arrangement of macrofibrils useful to a plant cell?
Allows water to move through and along cell walls, and water can pass in and out of the cell easily.
It also determines how cells can grow or change shape.
33
Why are turgid cells useful?
They support the whole plant
34
What are the functions of proteins?
They are structural components; they are membrane carriers and pores; all enzymes are proteins; antibodies are proteins; many hormones are proteins
35
What are proteins made of?
A long chain of amino acids joined end to end
36
What is the basic structure of an amino acid?
An amino group at one end of the molecule, an acid group at the other end of the molecule, and a carbon in between.
There is a hydrogen atom and a R-group coming from the carbon. Only the R-group differs between amino acids.
37
What are essential amino acids?
Amino acids that animals cannot build from materials they take into their own bodies - they are an essential part of the diet.
38
Why can surplus amino acids not be stored by the body?
The amino group makes them toxic if too much is present
39
What is deanimation?
The process in which the amino group is removed from an amino acid and converted into urea, then removed in the urine. Takes place in the liver.
40
When amino acids join together, what type of bond forms and what is the molecule called that forms?
A peptide bond; a dipeptide (if there are 2) or a polypeptide (if there are more than 2)
41
Where are polypeptides and proteins made (synthesised)?
In cells, on ribosomes
42
What is the role of messenger RNA (mRNA)?
Provides the information to put amino acids in the right order to make a specific polypeptide chain
43
What is a protein or polypeptide's primary structure?
The unique sequence of amino acids that make up the protein
44
Why do different proteins have different properties?
The sequence of amino acids found in a protein will have an effect on its properties
45
What catalyses the formation and breakage of peptide bonds?
Enzymes: protease enzymes catalyse the breakdown of peptide bonds.
46
What determines the overall shape of a polypeptide, and the number of coils/pleats?
The types of amino acids being added/the original sequence of amino acids (the primary structure)
47
What shape is the secondary structure of alpha glucose?
Helix
48
What shape is the secondary structure of beta glucose?
Pleated sheet
49
What holds the amino acid coils in place in a secondary structure?
Hydrogen bonds
50
What is the tertiary structure?
The overall 3D structure of the final polypeptide or protein molecule
51
What effect does heating a protein have?
- Increases the kinetic energy in the molecule
- This causes the molecule to vibrate, which breaks some of the bonds holding the tertiary structure in place
- Most of these bonds are quite weak, so they are easily broken
- If enough heat is applied, the whole tertiary structure can unravel and the protein will no longer function (denaturation)
52
What are the 2 different 3D shapes that proteins usually are?
Ball-shaped structure (globular protein)
| Fibres (fibrous protein)
53
What role do globular proteins usually have?
Metabolic roles
54
What roles do fibrous proteins have?
Structural
55
Are globular proteins usually soluble or insoluble in water?
Soluble
56
Are fibrous proteins usually soluble or insoluble in water?
Insoluble
57
Definition of quaternary structure
Protein structure where a protein consists of more than one polypeptide chain
58
What does haemoglobin's quaternary structure consist of?
4 polypeptide subunits:
- 2 are called a-chains
- 2 are called ß-chains
These together form 1 haemoglobin molecule, which is a water-soluble globular protein
59
What is the tertiary structure held in place by?
A number of bonds and interactions:
- disulfide bonds
- ionic bonds
- hydrogen bonds
- hydrophobic and hydrophilic interactions
60
What is a collagen molecule made up of?
- 3 polypeptide chains would around each other
- Each of the 3 chains is itself a coil, made up of around 1000 amino acids
- Hydrogen bonds form between the chains
61
What gives the structure of collagen strength?
Hydrogen bonds between the polypeptide chains
Each collagen molecule forms covalent bonds (cross-links) with other collagen molecules next to it:
- The cross-links are staggered along the collagen molecules, adding to the strength of the molecule
- Results in a structure called a collagen fibril
62
What is the function of collagen?
To provide mechanical strength in many areas
63
Name 3 differences between haemoglobin and collagen
- H = globular protein, C = fibrous protein
- H = soluble in water, C = insoluble in water
- H = contains a prosthetic group (haem), C = no prosthetic group
- H = wide range of amino acid constituents in primary structure, C = approx. 35% of the molecule's primary structure is 1 type of amino acid (glycine)
- H = much of the molecule is wound into alpha helix structures, C = much of the molecule consists of left-handed helix structures
64
Name 4 functions of lipids in living organisms
- A source of energy
- Energy storage
- All biological membranes are made from lipids
- Insulation
- Protection
- Some hormones are lipids
65
What is the solubility of lipids?
Soluble in organic solvents, but insoluble in water
66
What is a fatty acid?
A hydrocarbon chain with an acid group at one end
67
How does introducing a C=C double bond affect the hydrocarbon chain?
It changes the shape, which makes the molecules in a lipid push apart and so makes them more fluid
68
What does a triglyceride consist of?
1 glycerol molecule bonded to 3 fatty acid molecules
69
How are fatty acid molecules in a triglyceride joined to the glycerol molecule?
- A condensation reaction between the acid group of a fatty acid molecule and the OH groups of the glycerol molecule
- Forms a covalent bond
- Called an ester bond
- Produces a water molecule
- Produces a new molecule called a monoglyceride
70
How is a triglyceride molecule formed?
- Condensation reactions between acid groups of all 3 fatty acid molecules with the 3 OH groups
71
Why are triglycerides insoluble in water?
- The charges on the molecule are distributed evenly around the molecule
- So hydrogen bonds cannot form water molecules
72
Describe the structure of a phospholipid molecule
- Consists of a glycerol molecule with fatty acid molecules bonded by condensation reactions to produce ester bonds
- A phosphate group is covalently bonded to the 3rd OH on the glycerol, instead of a fatty acid
- This bonding occurs by a condensation reaction
73
How can an organism control the fluidity of phospholipid?
They can change the number of unsaturated fatty acids (more unsaturated = more fluid)
74
How are lipids respired?
- The ester bonds holding the fatty acids and glycerol together are hydrolysed
- Both the glycerol and fatty acids can then be broken down completely to carbon dioxide and water
- This releases energy, which is used to generate ATP molecules
75
Why do lipids not affect the water potential of the cell?
They are insoluble in water, so they can be stored in a compact way
76
What is the structure of cholesterol?
- 4 carbon-based ring structures join together
- Small molecule
- A type of lipid
77
Why can excess cholesterol be bad for humans?
- In bile, cholesterol can stick together to form gallstones
- In blood, cholesterol can be deposited in the inner linings of blood vessels causing atherosclerosis, which can result in a number of circulatory problems
78
Why is water a good transport medium?
- It remains liquid over a large temperature range
| - Can act as a solvent for many chemicals
79
How can you test for starch?
- Add a few drops of iodine solution
| - If starch is present, the solution will change from brown to blue/black
80
How can you test for a reducing sugar?
- Add Benedict's solution and heat to 80 degrees Celsius in a water bath
- If a reducing sugar is present, the solution will change from blue to orange-red
81
How can you test for a non-reducing sugar?
- If reducing sugar is negative, boil with hydrochloric acid
- Cool and neutralise with sodium hydrogencarbonate solution or sodium carbonate solution
- Repeat Benedict's test
- If a non-reducing sugar is present, the solution will change from blue to orange-red in the 2nd test
82
How can you test for a protein?
- Add Biuret reagent
| - If a protein is present, the solution will change colour from blue to lilac
83
How can you test for a lipid?
- Add ethanol to extract (dissolve) lipid and pour alcohol into water in another test tube
- If a lipid is present, a white emulsion will form near the top of water
84
How can you estimate the concentration of a reducing sugar?
- A Benedict's test reveals an orange-red precipitate
- The more reducing sugar there is present, the more precipitate will be formed, and the more Benedict's solution will be 'used up'
- If the precipitate is filtered out, then the conc of the remaining solution can be measured
- This will tell you how much Benedict's solution has been used up, so you can then estimate the conc of the reducing sugar
85
How does a colorimeter work?
- It shines a beam of light through a sample, and a photoelectric cell picks up the light that has passed through
- It will give a reading showing how much light has passed through
- Place the solution in a sample chamber between the light and the photoelectric cell in a small clear plastic container (a cuvette)
- The more copper sulfate that is used up in Benedict's test in a sample, the less light will be blocked out and the more light will be transmitted
- So the readings taken give a measure of the Benedict's reaction
86
When using a colorimeter, why do you need to make a calibration curve?
- Using a colorimeter doesn't tell you how much reducing sugar is present - it simply tells us which sample contains more
- A calibration curve can be used to quantify the amount
87
How can you prepare a calibration curve?
- Carry out a Benedict's test on a range of known concentrations of reducing sugars
- Then filter the precipitate out of the solution
- Use a colorimeter to give readings of the amount of light passing through the solutions
- Plot the readings on a graph to show light getting through (transmission) against reducing sugar conc
88
What are nucleotides?
The monomers of all nucleic acids
| - 3 subunits are joined by covalent bonds to form a single nucleotide molecule
89
How is a nucleotide formed?
By bonding together:
- A phosphate group
- A sugar molecule (usually a 5 carbon sugar - either deoxyribose (in DNA) or ribose (in RNA)
- A nitrogenous base (adenine, thymine, guanine, uracil or cytosine)
90
What are the 2 forms of nucleic acid?
DNA (deoxyribose nucleic acid) and RNA (ribonucleic acid)
91
What is the role of DNA and RNA in living organisms?
To hold the coded information to build that organism
92
How do nucleotides join together?
- A condensation reaction between the phosphate group of 1 nucleotide and the sugar of another nucleotide
- Repeating this bonding gives a long chain of nucleotides
93
How is a nucleic acid formed?
By chains of nucleotides bonding together
| - Only nucleotides carrying the same sugar molecule bind together bind together to form long-chained polymers
94
What is a purine molecule? Give 2 examples.
- A nitrogenous base consisting of a double ring structure
| - Adenine and guanine
95
What is a pyrimidine molecule? Give 2 examples
- A nitrogenous base consisting of a single ring structure
| - Thymine, uracil, cytosine
96
How is a DNA molecule formed?
2 polynucleotide strands come together:
- They form what looks like a ladder
- The sugar phosphate backbones of the 2 chains form the uprights
- The bases project towards each other to form the rungs
- There are hydrogen bonds between the bases
97
Why is DNA a stable structure, and why is this important?
- The hydrogen bonds between the bases in opposite uprights strengthen the rungs of the ladder
- Important because DNA carries the instructions to make an organism
- If it were unstable, the instructions could go wrong too easily
98
Why is 'antiparallel' used to describe DNA strands?
- They run in opposite directions to each other
| - The sugars are pointing in opposite directions
99
How do bases join up in DNA?
A pyrimidine always joins with a purine:
- Adenine always joins with thymine (they are complementary)
- Guanine always joins with cytosine
Hydrogen bonds form between the bases
100
How is a new copy of a DNA molecule made?
- The double helix is untwisted
- Hydrogen bonds between the bases are broken apart to unzip the DNA, which exposes the bases
- Free DNA nucleotides are hydrogen-bonded onto the exposed bases according to the base-pairing rules
- Covalent bonds are formed between the phosphate of 1 nucleotide and the sugar of the next to seal the backbone
- This is semi conservative replication
101
What shape is a complete DNA molecule and how is it formed?
A double helix:
| - The antiparallel chains twist
102
Why is DNA replication described as semi-conservative replication?
Each new DNA molecule consists of 1 conserved strand plus 1 newly built strand
103
How is the structure of DNA adapted to its function?
- Information is stored in the form of codes to form proteins
- The molecules are long so a large amount of info can be stored
- The base-pairing rules mean that complementary strands of info can be replicated
- The double helix structure gives the molecule stability
- Hydrogen bonds allow easy unzipping for copying + reading info
104
How is RNA structurally different to DNA?
- The sugar molecule that makes up the nucleotides is ribose
- Uracil is found instead of thymine
- The polynucleotide chain is usually single-stranded
- 3 forms of RNA exist
105
What are the 3 forms of RNA?
- Messenger RNA (mRNA)
- Ribosomal RNA (rRNA)
- Transfer RNA (tRNA)
106
How is mRNA made?
As a strand complementary to 1 strand of a DNA molecule:
| - It is a copy of the other DNA strand (the coding strand) of the double helix
107
What does tRNA do?
Carries amino acids to the ribosomes in the correct order:
- According to the base sequence on the mRNA
- They are then bonded together to form polypeptides
108
What does mRNA do after replication?
It is a copy of the DNA coding strand:
- The mRNA peels away from the DNA and leaves the nucleus through a nuclear pore
- It then attaches to a ribosome
109
What is the 3D structure of a globular protein?
- Hydrophobic amino acid R-groups in the centre of the 'ball'
- Hydrophilic amino acid R-groups around the outside of the ball
110
How are all enzymes similar?
- Globular proteins
- Generally soluble in water
- Act as catalysts
- Specific (catalyse reactions involving only 1 type of substrate)
- The globular structure has a 'pocket' called an active site
- Their activity is affected by temp and pH
111
Definition of catalyst
A molecule that speeds up a chemical reaction but does not get used up in the reaction
112
Definition of extracellular enzymes
Catalyse reactions outside the cell
113
Definition of intracellular enzymes
Catalyse reactions inside the cell
114
Definition of activation energy
- The amount of energy that must be applied for a reaction to proceed
- Different reactions require different levels of activation energy
- Enzymes reduce the amount of activation energy needed to allow a reaction to proceed
115
How so enzymes reduce the amount of activation energy required?
- An enzyme has a specifically shaped active site
- Complementary to the shape of the substrate molecule involved in the reaction
- So the substrate molecule can fit into the active site
- The shape of the enzyme changes as the substrate binds to the active site (induced-fit hypothesis)
116
What is the induced fit hypothesis?
- As a substrate molecule collides with an enzyme's active site, the enzyme molecule changes shape slightly
- This makes the active site fit more closely around the substrate
- The substrate fits in place and is also held because oppositely charged groups on the substrate and the active site are found near to each other (enzyme-substrate complex)
- This change in shape also places a strain on the substrate molecule, which destabilises it, so the reaction occurs more easily
- This produces a product (enzyme-product complex)
- The product formed is a different shape from the substrate
- The product no longer fits into the active site so moves away
117
When can an enzyme catalyse a reaction?
When the substrate molecule randomly collides with the active site of the enzyme so that an enzyme-substrate complex is formed
118
What is denaturation?
A change to the tertiary structure of an enzyme such that it cannot function and its function cannot be restored
119
What is an enzyme's optimum temperature?
The temperature that gives the maximum rate of reaction
120
What is pH?
A measure of the hydrogen ion concentration:
| - the higher the conc of H^+, the lower the pH value
121
How does a change in pH affect an enzyme?
- Hydrogen ions can interfere with the hydrogen bonds and ionic bonds holding the tertiary structure in place, because of their positive charge
- So increasing/decreasing the conc of H+ ions can alter the tertiary structure, leading to a change in shape of the active site
122
What is an enzyme's optimum pH?
- The pH at which the rate of reaction is highest
| - The conc of hydrogen ions in solution gives the tertiary structure of the enzyme the best overall shape
123
What is a buffer?
A chemical solution that resists changes in pH by maintaining a constant level of hydrogen ions in solution
124
What effect does increasing the substrate concentration have on a reaction?
- Collisions between enzyme and substrate molecules occur more often
- More enzyme-substrate complexes form
- So more product is formed
The reaction rate increases
125
Why does the substrate conc reach a point where the rate of reaction reaches a maximum value?
- At this point, all the enzyme molecules present are forming enzyme-substrate complexes as fast as possible
- All the active sites are occupied at all times
- Any further increase in substrate conc will have no effect on the reaction rate
126
What effect does increasing the enzyme concentration have on a reaction?
- As the enzyme conc increases, more active sites become available
- More enzyme-substrate complexes form, so the rate of reaction increases
127
Why does the enzyme conc reach a point where the rate of reaction reaches a maximum value?
- At this point all substrate molecules are occupying enzyme active sites
- So increasing the enzyme conc will have no effect on the reaction rate
128
What is a limiting factor?
- A variable that limits the rate of a process
| - If it is increased, then the rate of the process will increase
129
In an experimental situation where enzyme and substrate are mixed together, when will the rate of the enzyme-controlled reaction be highest?
At the point when enzyme and substrate are mixed:
- As the reaction proceeds, product molecules are formed and increase in number
- At the same time, substrate molecules are used up and decrease in number
- So the frequency of collisions between enzyme and substrate goes down as an enzyme-controlled reaction proceeds
130
How can you regulate enzyme activity?
By adjusting the conc of enzymes and/or substrates
131
What is an enzyme inhibitor?
A substance or molecule that slows down the rate of an enzyme controlled reaction by affecting the enzyme molecule in some way
132
How do competitive inhibitor molecules work?
- They have a similar shape to that of the substrate molecules
- So they can occupy the active site instead of the substrate, forming enzyme-inhibitor complexes
- These complexes do not lead to the formation of products because the inhibitor is not identical to the substrate
- The enzyme doesn't catalyse a reaction
- The number of enzyme-substrate complexes is reduced, so the reaction rate slows down
133
How do non-competitive inhibitors work?
- They attach to the enzyme molecule in a region away from the active site
- This distorts the tertiary structure of the enzyme molecule
- This leads to a change in the active site
- So the substrate no longer fits into the active site, so enzyme-substrate complexes cannot form and the reaction rate decreases
134
What does the level of competitive inhibition depend on?
The concentrations of inhibitor and substrate
135
What does the level of non-competitive inhibition depend on?
The number of inhibitor molecules present
136
How permanent are inhibitors?
Competitive:
- bind to the active site for a short period and then leave
- their action is reversible
Non-competitive:
- Bind permanently to enzyme molecules
- Irreversible
- An enzyme molecule bound by inhibitor molecules is effectively denatured
137
What is a cofactor?
Any substance that must be present to ensure enzyme-controlled reactions take place at the appropriate rate
138
What are coenzymes?
Small, organic, non-protein molecules that bind for a short period to the active site
139
How do coenzymes work?
- May bind just before, or at the same time as, the substrate binds
- Often take part in the reaction and are changed in some way
- They are recycled back to take part in the reaction again
- They carry chemical groups between enzymes so they link together enzyme-controlled reactions that need to take place in sequence
140
What is a prosthetic group?
- A coenzyme that is a permanent part of an enzyme molecule, and is vital to the function of the molecule
- Contributes to the final 3D shape, and to other properties of the molecule, including its charges
141
How do inorganic ion cofactors work?
- The presence of certain ions can increase the reaction rate
- They may combine with either the enzyme or the substrate
- This allows the enzyme-substrate complex to form more easily, because it affects the charge distribution and sometimes the shape of the enzyme-substrate complex
142
How do antibiotics work?
They can kill or inhibit the growth of microorganisms
143
What the the turnover number of an enzyme?
The number of reactions an enzyme molecule can catalyse in 1 second
144
How would a lack of enzymes affect metabolic reactions?
They would not occur at a high enough rate to support any living processes
145
How do enzyme-controlled reactions help metabolic processes?
- The product of 1 enzyme-controlled reaction is the substrate for the next enzyme-controlled reaction in the sequence (metabolic pathway)
- The end product of the sequence often attaches to one of the enzymes early in the sequence
- This is the same as reversible non-competitive inhibition
146
What is a sucrose molecule made from?
Glucose and fructose
147
What is a lactose molecule made from?
Glucose and galactose
148
What is a maltose molecule made from?
2 alpha glucose molecules
149
How can you investigate enzyme activity?
By measuring:
- The rate at which substrate is used up
- The rate at which product is formed
Allows you to measure the reaction rate
150
How can you calculate the rate of reaction?
1/time
151
Name 5 useful properties of water
- Solvent
- Liquid over a large range of temps
- Surface tension at the water surface
- Water freezes, forming ice on the surface, but it is still water underneath (becomes insulated)
- Large bodies of water have fairly constant temps
- Evaporation of water can cool surfaces by removing heat
- Takes part as a reactant in some chemical processes
152
How is surface tension created at the water surface?
Water molecules stick to each other due to forces of cohesion
153
Why does water remain liquid over a large temperature range?
The hydrogen bonds in liquid water restrict the movement of the water molecules, so a relatively large amount of energy is needed to increase the temp of water
154
Why is water a good transport medium?
- Can act as a solvent for many chemicals
| - Remains liquid over a large temperature range
155
How does water dissolve polar molecules?
- The solute has slightly negative and slightly positive parts
- The water molecules cluster around the slightly charged parts of the solute molecule
- This keeps solute molecules apart, so they are dissolved
- Once in solution, molecules can move around and react with other molecules
156
How are cholesterol and carbohydrates similar?
They both have OH groups, contain C,H and O and have hex/pent ring
157
How can DNA differ?
Different alleles
Different sequence
Different number of bases
158
Suggest why the lock-and-key and induced-fit explanations are termed models.
Makes the process easier to understand
159
Explain how the properties of water help organisms survive in a pond
(8 marks)
Ice floats because the water molecules spread out into a crystalline structure, which insulates the pond so it is warmer for organisms underneath.
Water dissolves ions by the ions attracting the water molecules because of their charges. Nitrate ions are used for a plant to grow as it is needed in amino acids.
Water is transparent so plants get the light needed for photosynthesis which allows them to release oxygen which is needed for respiration of other organisms.
The temperature is constant in the pond because the water has a high heat capacity because evaporation causes the water to remain cool. Also, hydrogen bonds mean water molecules cannot move much. Water is a liquid over a large range of temperatures so gases remain soluble. Also, it means enzymes work at their optimum temperature because the temperature is constant.
160
Explain how a molecule can act as a competitive inhibitor.
| 3 marks
It has a similar shape to the substrate, which has a functional group which is complementary to the active site of the enzyme, so it can fit in active site, blocking the active site so the substrate cannot move in so enzyme-substrate complexes cannot form.
161
Explain the effect of increasing the concentration of substrate on a reaction with a competitive inhibitor.
(2 marks)
Inhibitor competes for the active site. It occupies the active site for a short period of time. This means fewer active sites available for substrate. A higher concentration of substrate reduces the chance of inhibitor getting in.
162
Explain how the final product the DNA codes for can be affected by changing the sequence of DNA nucleotides. (2 marks)
Different amino acid sequence, so a different tertiary structure, giving it a different function.
163
Describe the structure of a triglyceride molecule. (3 marks)
Glycerol molecule attached to three fatty acids by ester bonds.
164
Explain why different enzymes are involved in each stage of the digestion process. (3 marks)
Enzymes are specific.
Substrates have a specific shape which is complementary to the shape of the active site. This means enzyme-substrate complexes can form due to induced fit hypotheses.
165
Explain why the activity of an enzyme of optimum pH 3 falls to 0 at 7pH. (3 marks)
pH much higher than optimum.
Changes charge of the active site.
Hydrogen bonds break, so tertiary structure altered. The enzyme denatures so the substrate can no longer fit in the active site.
166
Explain why you need large amount of protein in the diet whereas small amounts of vitamins and minerals are needed (1 mark)
Cofactors are recycled.
167
Suggest two ways in glucose is adapted to its function in living organisms (2 marks)
Soluble.
| Easily respired to produce ATP energy
