2. Control of Eukaryotic Gene Expression

Question 1

What is the advantage of control of gene expression at the level of translation over control
of gene expression at the level of transcription.

Answer 1

1. Faster formation of protein in the cell (as not needed to activate transcription of gene);
2. Possible even if nucleus is absent from cell;
3. Provides a mean for cell to cope with rapid changes in protein concentrations;

Question 2

Explain why such addition of poly A tail to mature mRNA is necessary for its stability and translation initiation.

Answer 2

Effects on stability

a) longer time needed for poly-A tail to be shortened
b) before mRNA degradation occur/to reaches critical length/increasing the half life of mRNA

Effects on translation initiation
a) idea of longer tail helps in the assembly/recruiting of the translation initiation factors at
the 5’ cap

Question 3

Explain why alternative splicing is essential in eukaryotic cells from an evolutionary view point.

Answer 3

1. This process allows a single gene to code for many different types of proteins than would be expected from its fixed protein-coding genes
2. Particular exons of a gene may be included within, or excluded from, the final, processed messenger RNA (mRNA) produced from that gene.
3. Ref to proteins translated from alternatively spliced mRNAs will contain differences in their amino acid sequence and, often, in their biological functions leading to variations to occur in a population.

Question 4

Explain why activator contains both a DNA-binding domain and a protein-binding
domain.

Answer 4

a. DNA-binding domain binds to specific DNA sequences/ nucleotide sequences that make up enhancer;
b. Protein-binding domain binds to other transcription factors / RNA polymerase / DNA bending protein / Mediator protein;
c. to stabilize the transcription initiation complex and thus enable it to bind securely on the
promoter;
d. increase rate of transcription;

Question 5

Regulation of gene expression at post transcriptional level occurs in eukaryotes. State why it is absent in prokaryotes.

Answer 5

Prokaryotes lack a nuclear envelope, no regulation at/by the membrane does not occur