Question

will rate - thanks

1 - The retinoblastoma protein (RB or pRB) is an important checkpoint protein that blocks expression of cyclin E and cyclin A when it is not phosphorylated. What would be the consequence to the cell if the RB protein were mutated and could no longer be phosphorylated?

A: The cell would continuously replicate regardless of other signals

B: The cell could not progress through the cell cycle and replicate

2 - In the case of HER2 and the development of breast cancer, which of the following is TRUE?

A: The HER2 receptor is overexpressed on the surface of mammary cells.

B: The HER2 gene is required for metastasis of the malignant cells

3 - Which of the following statements about translation is/are TRUE?

A: Translation of mRNA into a protein requires cellular energy in the form of GTP

B: Transfer RNA that corresponds to the STOP codons carry a termination factor instead of amino acids

4 - Consider a protein destined to be located in the nucleus of the cell. Which of the following is FALSE?

A: The protein itself would contain a nuclear localization sequence (NLS)

B: The translation of nuclear protein must occur within the nucleus of the cell before translocation into the endoplasmic reticulum

Answer 1

1. Correct answer: B The cell could not progress through cell cycle and replicate. Rb protein is a tumor suppressor protein that prevents excessive cell growth by inhibiting cell cycle progression by regulating the cell to remain in G0/ G1 stage until a cell is ready to divide. In phosphorylated state the Rb protein in inactive, the cell cycle progression occurs normally. When this protein is mutated and no longer able to phosphorylate,the Rb protein remains in active state arresting the cell in G0 phase as a result the cell won't progress through cell cycle and divide.

2. Correct answer: A. The HER2 receptor is overexpressed on the surface of mammary cells. The HER2 gene makes HER2 proteins which act as a receptor on mammary cells. These receptors help to control how a mammary cell grows, divides and repair itself. A mutation in HER2 gene would cause overexpression of the receptors which leads to uncontrolled growth of mammary cells leading to cancer.

3. Correct answer: A and B. Both the statements are true in regards with translation. Translation of mRNA requires help of various factors (initiation, elongation and termination factors) for each stage of translation. Some of these factors are boung to GTP and utilize the energy from GTP hydrolysis to perform their function. So the statement that translation of mRNA into protein require cellular energy in the form of GTP is true. Stop codons are the codons that terminate translation of mRNA when present in mRNa sequence. These codons are recognised by termination factors which terminate translation. Instead of amino acid, transfer RNA corresponds to stop codon by carrying terminating factors, which recognise these stop codons, terminate translation and release the polypeptide chain.

4. Correct answer: B. The statement the translation of nuclear proteins occur within the nucleus of the cell before the translocation into endoplasmic reticulum is false. The proteins that are bound for nucleus are usually made in cytosol, where translation takes place as ribosomes and rough endoplasmic reticulum are present in cytosol. The protein destined to nucleus contains nuclear localization signal which direct the vesicles to transport the protein to nucleus, where they fulfill their role.