Unit 8 - 3.8.2 Gene expression

Question 1

The KRAS gene codes for a protein called K-Ras. The protein relays signals from outside a cell to a cell’s nucleus, stimulating cell division. An alteration in the KRAS gene produces an oncogene which can cause a tumour to develop.

Suggest and explain how an alteration in the KRAS gene can cause a tumour to develop. (3)

Answer 1

1. Mutation (in KRAS gene) OR Change in base sequence (of KRAS gene);

Accept named mutation e.g. substitution. Accept mutation in promoter gene.

Ignore epigenetic modifications.

2. Change in (signalling) protein

OR More (signalling) protein/K-Ras produced;

Accept change in amino acid sequence (of protein).

Reject ‘no protein produced’ or suggests a non-functional protein is produced.

3. (Results in) rapid/uncontrollable cell division;

Accept cell division cannot be regulated. Ignore growth.

Reject meiosis for cell division, but accept mitosis

Question 2

Myelodysplastic syndromes (MDS) are a group of malignant cancers. In MDS, the bone marrow does not produce healthy blood cells.

Haematopoietic stem cell transplantation (HSCT) is one treatment for MDS. In HSCT, the patient receives stem cells from the bone marrow of a person who does not have MDS. Before the treatment starts, the patient’s faulty bone marrow is destroyed.

(a)  For some patients, HSCT is an effective treatment for MDS. Explain how.

Answer 2

1. Produce healthy (blood) cells;

Accept produce ‘normal’ /non-MDS cells.

2. No MDS/faulty/cancerous (blood) cells;

Produce only healthy/normal (blood) cells = two marks.

Accept no (cancerous) tumour.

3. Stem cells divide/replicate;

Ignore reference to totipotent/pluripotent/ multipotent/unipotent

Accept ‘clone’ for divide.

Question 3

Myelodysplastic syndromes (MDS) are a group of malignant cancers. In MDS, the bone marrow does not produce healthy blood cells.

Scientists investigated the effectiveness of AZA in patients with MDS. A total of 360 patients were randomised in the ratio of 1:1 to receive AZA or conventional drugs (control).

The control patients were treated with conventional drugs.

Give two reasons why.

Answer 3

1. Effect of AZA can be compared;

Comparison on its own is not enough for a mark.

2. Unethical not to treat (control group);