EQ - Genes and health

Describe the function of DNA polymerase in producing a polynucleotide. (2)

catalyses condensation reactions

joining together DNA mononucleotides

to form phosphodiester bonds (between the pentose sugar of one nucleotide and the phosphate grouo of another nucleotide)

Describe the role of tRNA in the production of myosin

tRNA transports amino acids to the ribosomes

tRNA molecule has an anticodon that binds to a codon on mRNA

each tRNA molecule carries a particular amino acid

Explain why the enzyme catalase is describe as having a tertiary and quaternary structure (3)

enzymes have a tertiary structure whereby polypeptide chains are held together by bonds such as ionic and hydrogen bonds and disulphide bridges between R groups → this would form a 3D tertiary structure

has a quaternary structure as it has more than one polypeptide chains with a prosthetic group hence is a quaternay structure

Describe how the primary structure of leptin enables it to be soluble in water (3)

primary structure etermines the folding of the polypeptide chain

forming a globular protein

whereby hydrophilic R groups are on the outside of the protein

so water can form hydrogen bonds with the protein

Explain why a mutation in the base sequence of haemoglobin would affect the function of the haemoglobin molecule (4)

change in the base sequence results in a different triplet code being produced

thus results in a change in amino acids

this would change the bonds formed between R groups —→ causing a change in the tertiary structure

thus haemoglobin would no longer be able to bind to oxygen

The thick filament in a myofibril contains myosin. The myosin head contains the enzyme ATPase.

Explain the importance of the primary structure for the functioning of this enzyme. (3)

primary structure determines the interaction between R groups

primary structure determines the folding of the polypeptide

therefore affecting the shape of the active site

the active site is complementary to ATP

Haemophilia is a disease that affects blood clotting. People with haemophilia are sometimes given a protein called factor VIII. Factor VIII is an enzyme that is involved in the process of blood clotting.

Explain how a change in the primary structure of factor VIII could cause difficulties with blood clotting. (4)

a change in the primary structure means a different sequence of amino acids and therefore a change in the folding of the polypeptide

this causes a change in the bonds e.g ionic or disulphide birdges, formed between R groups —→ causing a change in the tertairy structure

thus the shape of the active site is changed

so the active site can no longer bind to the substrate

thus reducing fibrin production

Explain how a single base sequence mutation can lead to altered primary structure of an enzyme (3)

a change in the base sequence means that a change in the triplet code is

thus cahnges the codons in the mRNA

resulting in a change in the amino acid sequence

this causes a change in the folding of the polypeptide

Explain why enzymes that are incorrectly folded cannot carry out their function (3)

this results in a change in the 3D tertiary structure of the enzyme

a change in the shape of the active site

therefore the substrate is no longer able to bind to the active site of the substrate

therefore the enzyme cannot catalyse the reaction so no enzyme-substrate complexes are produced

Explain how a change of one amino acid could lead to a change in the structure and properties of the haemoglobin protein (4)

a change in the amino acid means a change in the triplet code produced

therfore a different sequence of amino acids

thus a change in the folding of the polypeptide chain

this results in a change in the bonds e.g ionic bonds between R groups causing a change in the tertiary structure

therefore haemoglobin can no longer bind to oxygen

Describe how the structure of phospholipase allows it to hydrolyse phospholipids (4)

specific squence of amino acids results in a specific folding of the polypeptide chain

this would form specific bonds between R groups e.g disulphide bridges —→ forming a tertiary structure / globular shape

the globular shape provides a specific active site which is complementary to part of the phospholipid

hence the phospholipids can bind to the active site of phospholipase

thus can catalyse the reaction to break bonds between fatty acids and glycerol

• using the measuring cylinder measure the volume of oxygen produced in 5 minutes

• plot a graph and calculate the gradient from 0 to calculate the initial rate of reaction

• use the same volume of hydrogen peroxide e.g 10 cm³

• use mussels of the same age

• repeat the investigation for each mussel type three times to calculate a mean and elimate any anomalies

Explain why it is necessay to measure the initial rate of reaction when investigating the effect of enzyme concentration on the rate of reaction

at the start the substrate is not a limitting factor

as the reaction progresses the concentration of substrate decreases

lower concentrations of substrate limits the rate of reaction

Describe an experiment that could be carried out to investigate the effect of enzyme concentration on the initial rate of reaction.

1. use at least 5 different enzyme concentrations e.g 0.2%, 0.4%, 0.6%, 0.8%,1.0% and 1.2%.

2. place 10 cm³ of substrate and 7 cm³ of enzyme concentration in a water bath at 30^o C

3. mix both the solutions in a glass beaker

4. start a timer and measure the change in pH at regular intervals or the volume of product released over 5 minutes

5. plot a graph then calculate the gradient from the linear part of the graph - calculating the initial rate of reaction

6. repeat using different concentrations of enzyme yet keeping the temperature constant using a water bath

7. repeat using no enzyme concentration as a control

Explain why a buffer solution should be used in a enzyme-controlled reaction (4)

buffer solution controls the pH

this is because a change in the pH would result in a change in the shape of the active site

this is because a change in the pH affects the ionic bonds within the enzyme

therefore a change in the rate of reaction

Cofactors are non-protein molecules that help enzymes to function.

Magnesium ions act as cofactors for some enzymes.

Devise an experiment to investigate the effect of magnesium ions on the initial rate of this reaction (5)

• add 10 cm³ of isomerase enzyme solution in one test tube and 7cm³ of substrate solution in another test tube

• combine the two test tubes together then start a timer, measure the mass of fructose produced at regular intervals

• plot a graph then calculate the initial rate of reaction from the gradient of the linear part of the graph

• use excess substrate so that substrate is not limitting

• control temperature using a water bath

• repeat to calculate a mean

• repeat with and without magnesium ions