Exam-style Questions

1. Read the following passage and then answer the questions that follow.

Cancers occur when cell division gets out of control. Faults in a gene called p53 are associated with nearly all cancers. A test that could be used to detect a faulty p53 gene would obviously be a good idea.

There are genes in a cell that prevent it dividing. The protein produced by the p53 gene switches on these genes and so stops cell division. If p53 stops working the cell is likely to become cancerous.

Faulty p53 can now be detected simply and cheaply with a test based on yeast. The test is much cheaper than gene sequencing. It is much more reliable because knowing the sequence of bases in a DNA molecule does not allow us to distinguish harmless mutations from potentially harmful ones.

The new test works by inserting the p53 gene into yeast DNA in which another gene, called ADE2 has been inserted. If the p53 gene works, it switches on the ADE2 gene. As a result the yeast cells appear white in colour. If the p53 gene does not work, the ADE2 gene is not switched and the yeast cells appear red in colour.

a) (i) Draw a simple flow chart to show how the p53 gene helps to prevent cancer.

(ii) Explain how the product of the ADE2 gene might act to change the colour of the yeast cells.

b) Explain what is meant by gene sequencing.

(Marks available: 5)

Answer

Answer outline and marking scheme for question: 1

Give yourself marks for mentioning any of the points below:

a) (i) Flow chart showing:

p53 gene produces protein.

Protein switches on gene preventing cell division.

(ii) Red products converted into white;

ADE2 controls enzymes governing this step.

(4 marks)

b) Determining base and sequence (of gene)

(1 mark)

(Marks available: 5)

2. One of the aims of genetic engineering is to produce a protein as cheaply and easily as possible.

In order to do this, the gene that triggers production of the desired protein is inserted into a host organism.

a) State three reasons why bacteria make good host organisms.

b) (i) Define a vector in relation to genetic engineeing?

(ii) Define a plasmid in relation to genetic engineering?

(Marks available: 5)

Answer

Answer outline and marking scheme for question: 2

Give yourself marks for mentioning any of the points below:

a) Asexual reproduction, parent cells produce identical daughter cells.

Grow quickly.

Easily manipulated.

Has simple chromosome.

Contains plasmids.

(3 marks)

b) (i) A carrier DNA molecule, the desired gene can be inserted.

(ii) A small extrachromosomal circular piece of DNA naturally found in bacteria. Often used as a vector.

(2 marks)

(Marks available: 5)

3.a) (i) What is non-coding DNA?

(ii) Why is non-coding DNA used in genetic fingerprinting?

b) Suggest two uses for genetic fingerprinting.

(Marks available: 4)

Answer

Answer outline and marking scheme for question: 3

Give yourself marks for mentioning any of the points below:

a) (i) Does not code for a protein.

(ii) Contains repetitive sequence of bases/variable number tandem repeats

The size of these VNTRs varies according to the individual. Half come from one parent half from the other. only identical twins have the same VNTRs.

b) Identifying particular plants/animals with particular alleles of a gene for selective breeding.

Identifying a particular microbe so correct treatment can be given.

Establishing paternity

Confirming animal pedigrees.

Establishing genetic diversity for gene banking.

(Marks available: 4)