Question

Describe how each of the following mutations might affect progression through the cell cycle. Assume that “mutation” in this context means that a change in an allele ‘s DNA sequence causes a change in protein sequence that results in that protein losing its normal wild-type function in the cell.

1. Consider a cell line that contains one mutant copy of the Rb gene.

a) Describe (a) the normal function of Rb and

b) what would happen in cells heterozygous for wild-type Rb (this cell has one wild-type allele and one mutant allele of Rb).

2. What would happen in a cell line that contains two mutant copies of the Rb gene?

3. Consider a cell line that contains two mutant copies of the p53 gene.

a) Describe the normal function of p53, and

b) what would happen in cells with two mutant copies of the p53 gene.

Answer 1

1. a. Normal function of Rb gene

• Rb or Retinoblastoma gene is a tumor supressor gene.
• It can control cell cycle prevent uncontrolled cell growth of cells
• Protein encoded by Rb gene is called pRb
• Rb prevent the progression f cells from the G1 (first gap phase) to S

b. Cells  heterozygous for wild-type Rb ir one wild-type allele and one mutant allele of Rb will show normal phenotype. It do not cause any cancer or uncontrolled cell division. two-hit model best explain the working of Rb gene- both the alleles must be mutated to show the abnormal effect.

2. cell line that contains two mutant copies of the Rb gene develop tumors.

3a. Normal function of p53

• p53 is a tumor supressor gene
• It regulates cell division
• p53 are able to activate DNA repair, if the DNA do not undergo repair, the p53 will prevent the progression of cell into next stage.

b. If both the alleles for p53 is mutated, cells will undego cell divison with out repairing the DNA dammage. This will lead to cancerous condition and uncontrolled cell growth. Mutation of p53 is related to Breast cancer, Cholangiocarcinoma and Brain cancer