Thursday 26 May 2016

Question 1

Describe how the complementary strand of HIV DNA is made.

Answer 1

1. (Complementary) nucleotides
2. DNA polymerase;
3. Nucleotides join together (to form new strand)/phosphodiester bonds form;

Question 2

Contrast the structures of DNA and mRNA molecules to give three differences.

Answer 2

1. DNA double-stranded and mRNA single-stranded;
2. DNA long and RNA short;
3. Thymine/T in DNA and uracil/U in RNA;
4. Deoxyribose in DNA and ribose in RNA;

Question 3

Describe the difference between the structure of a triglyceride molecule and the structure of a phospholipid molecule.

Answer 3

In phospholipid, one fatty acid replaced by a phosphate;

Question 4

Describe how you would test for the presence of a lipid in a sample of food.

Answer 4

1. Add ethanol, then add water;

2. White (emulsion shows lipid);

Question 5

Describe how a saturated fatty acid is different from an unsaturated fatty acid.

Answer 5

Saturated single/no double bonds (between carbons)

Question 6

This fat substitute cannot be digested in the gut by lipase. Suggest why.

Answer 6

1. Not complementary;

2. Unable to fit/bind to (active site of) lipase/no ES complex formed;

Question 7

This fat substitute is a lipid. Despite being a lipid, it cannot cross the cell-surface membranes of cells lining the gut.
Suggest why it cannot cross cell-surface membranes.

Answer 7

It is hydrophilic/is polar/is too large/is too big;

Question 8

Describe how ATP is resynthesised in cells.

Answer 8

1. From ADP and phosphate;
2. By ATP synthase;
3. During respiration/photosynthesis;

Question 9

Give two ways in which the hydrolysis of ATP is used in cells.

Answer 9

1. To provide energy for other reactions/named process;

2. To add phosphate to other substances and make them more reactive/change their shape;

Question 10

What is the evidence from Figure 2 that a scanning electron microscope was used to take this photograph?

Answer 10

(Can see) 3D image;

Question 11

Transport through a channel protein

Answer 11

Facilitated diffusion

Question 12

Transport of small, non-polar molecules

Answer 12

Diffusion through the phospholipid bilayer

Question 13

Transport of glucose with sodium ions

Answer 13

Co-transport

Question 14

Y is a protein. One function of Y is to transport cellulose molecules across the phospholipid bilayer.
Using information from Figure 3, describe the other function of Y.

Answer 14

1. (Y is) an enzyme/has active site/forms ES complex;

2. That makes cellulose/attaches substrate to cellulose/joins β glucose;

Question 15

What is the evidence in Figure 3 that the phospholipid bilayer shown is part of the cell-surface membrane?

Answer 15

Cell wall forms outside cell-surface membrane

Question 16

Bond that holds the cellulose molecules together side by side.

Answer 16

Hydrogen

Question 17

Name the products of the hydrolysis of sucrose

Answer 17

• Fructose

- Glucose

Question 18

Describe the induced-fit model of enzyme action.

Answer 18

1. (before reaction) active site not complementary to/does not fit substrate;
2. Shape of active site changes as substrate binds/as enzyme- substrate complex forms;
3. Stressing/distorting/bending bonds (in substrate leading to reaction);

Question 19

The scientist used quantitative Benedict’s tests to produce a calibration curve of colorimeter reading against concentration of maltose.
Describe how the scientist would have produced the calibration curve and used it to obtain the results in Figure 4.
Do not include details of how to perform a Benedict’s test in your answer.

Answer 19

1. Make/use maltose solutions of known/different concentrations (and carry out quantitative Benedict’s test on each);
2. (Use colorimeter to) measure colour/colorimeter value of each solution and plot calibration curve/graph described;
3. Find concentration of sample from calibration curve;

Question 20

Human papilloma virus (HPV) is the main cause of cervical cancer. A vaccine has been developed to protect girls and women from HPV.
Describe how giving this vaccine leads to production of antibody against HPV.

Answer 20

1. Vaccine/it contains antigen (from HPV);
2. Displayed on antigen-presenting cells;
3. Specific helper T cell (detects antigen and) stimulates specific B cell;
4. B cell divides/goes through mitosis/forms clone to give plasma cells;
5. B cell/plasma cell produces antibody;

Question 21

What do these results suggest about whether it is better to give two or three doses of the vaccine? Give reasons for your answer.

Answer 21

1. Two (doses) because got more antibody;
2. With three doses, second dose/dose at 1 month doesn’t lead to production of any more antibody (than the two- dose group)/get same/similar response;
3. Three doses would be more expensive/less popular with parents/girls (and serves no purpose);

Question 22

The doctors carried out a statistical test to determine whether the antibody concentrations were significantly different in girls given two doses of the vaccine, compared with those given three doses. They determined the mean concentrations of antibody 9 months after the first dose of vaccine.
What statistical test should the doctors have used? Give the reason for your choice.

Answer 22

t-test, because comparing two means;

Question 23

There is genetic diversity within HPV.

Give two ways doctors could use base sequences to compare different types of HPV.

Answer 23

1. Compare (base sequences of) DNA;
2. Look for mutations/named mutations (that change the base sequence);
3. Compare (base sequences of) (m)RNA;

Question 24

Chromosomes line up on the equator of the mitotic spindle in

Answer 24

Metaphase

Question 25

Suggest why the development of a monopolar mitotic spindle would prevent successful mitosis.

Answer 25

1. No separation of chromatids/chromosomes/centromeres;
2. Chromatids/chromosomes all go to one pole/end/sides of cell/not pulled to opposite poles;
3. Doubles chromosome number in cell/one daughter cell gets no chromosomes or chromatids;

Question 26

Suggest how amyloid-precursor protein can be the substrate of two different enzymes, α-secretase and β-secretase (lines 3–5).

Answer 26

1. Different parts/areas/amino acid sequences (of amyloid-precursor) protein;
2. Each enzyme is specific /fits/binds/ complementary to a different part of the APP;

Question 27

One product of the reaction catalysed by β-secretase is a smaller protein (lines 6–7).
Describe what happens in the hydrolysis reaction that produces the smaller protein from amyloid-precursor protein.

Answer 27

1. Peptide bond broken;

2. Using water;

Question 28

Many people with Alzheimer’s disease have mutations that decrease α-secretase production, or increase β-secretase production (lines 8–9).
Use the information provided to explain how these mutations can lead to Alzheimer’s disease.
[3 marks]

Answer 28

1. Mutations prevent production of enzyme(s)/functional enzyme;
2. (Increase in β-secretase) leads to faster/more β-amyloid production OR
   (Decrease in α-secretase) leads to more substrate for β-secretase;
3. (Leads to) more/greater plaque formation;

Question 29

One possible type of drug for treating Alzheimer’s disease is a competitive inhibitor of β-secretase (lines 10–11).
Explain how this type of drug could prevent Alzheimer’s disease becoming worse

Answer 29

1. (Inhibitor) binds to/blocks active site of β-secretase/enzyme;
2. Stops/reduces production of β- amyloid/plaque;

Question 30

When some of these types of drugs were trialled on patients, the trials were stopped because some patients developed serious side effects (lines 11–13).
Using the information provided, suggest why some patients developed serious side effects.

Answer 30

1. Some β-amyloid required/needed (to prevent side effects)
   OR
   (Some) β-secretase needed;
2. Leads to build-up of amyloid-precursor protein (that causes harm)
   OR
   Too much product of α-secretase (causes harm);