Question

1. Which of the following is not an example of a posttranslational modification?

A. N-terminal amino acid(s) commonly removed or modified

B. signal/targeting peptide remova

l C. phosphorylation, methylation, acetylation

D. Glycosylation

E. All of the above are examples of posttranslational modifications

2. The major problem that arises from incorporating incorrect tautomers into a cell’s DNA is that:

A. they react with adjacent bases to form dimers.

B. they often lead to slippage problems during replication.

C. they cannot be transcribed into RNA, blocking gene expression.

D. they mispair, leading to replication errors.

E. All of the above are correct answers to the question.

3.An alkylating agent reacts with the double-bonded oxygen of a guanine base in a DNA molecule. The most likely result will be:

A. the base is locked into the incorrect tautomer.

B. that it will dimerize.

C. that it will fall out of the duplex as the n-glycosidic bond fails.

D. a strand break as the phosphodiester bond will fail.

E. a deletion in the DNA at this point.

4. The treatment of eukaryotic cells with 5-azacytidine is likely to:

A. cause a general reduction in gene expression.

B. activate a number of previously inactive genes.

C. cause mutations of the transition variety.

D. cause a shortening of telomeres.

E. block cell division in S phase.

5. In the context of eukaryotic gene expression, which of the following statements about enhancers is/are not true?

A. They can be upstream or downstream of the regulated promoter(s).

B. They can act over relatively large distances.

C. The element’s orientation is not important for function.

D. They are gene specific.

E. They may have binding sites for both activating and inhibitory factors

6.A study of one of your cells reveals that it has many DMs and HSRs. This suggests that it has:

A. a high level of heterochromatin.

B. an unstable genome.

C. engaged in extensive chromatin remodeling.

D. heavily damaged DNA.

E. entered into S phase and is replicating its DNA.

7.A protein thought to be involved in the process of activating a eukaryotic gene though the process of chromatin remodeling is:

A. HDAC.

B. HAT.

C. CAP.

D. photolyase.

E. CpG DNA methylase

8.. During the elongation phase of translation, the charged tRNA enters the ribosome at the: “

A. A” site.

B. AUG codon.

C. “E” site.

D. “P” site.

E.RBS.

9. A molecule with a planar conjugated ring structure interacts with an E. coli cell’s DNA in the “early” portion of a coding sequence for an essential enzyme and eventually leads to a mutation in this region. The likely result will be:

A. nonsense mutation.

B.missense mutation.

C. a silent mutation.

D. frameshift mutation.

E. conditional mutation.

Answer 1

1. E is correct. Post translational modification refers to covalent modofication of proteins after their biosynthesis. This includes addition of functional groups such as methyl , phosphoryl, lipid, glucose, acetyl groups to a protein. PTMs also include removal of amino acids or removal of small peptides from a protein also known as proteolysis.

2. D is correct. Tautomerisation of bases during replication, can lead to its mispairing with another base, leading to error in DNA replication.

3. A is correct. Alkylation is the addition of alkyl groups to DNA bases (such as alkylation of carbon atom 6 of guanine), this leads to change of a G:C base pair to a A:T base pair as the base is locked in an incorrect tautomer.

4. B is correct . Azacitidine is a drug that inhibits DNA methyltransferase causing hypomethylation of DNA, and DNA methylation results in repression of gene transcription or gene silencing. It also removes methyl groups from DAN, hence treatment of eukaryotic cells with this drug will lead to transcription of a number of previously inactive genes.