Question

Please write a different and clear answer not the common ones found on other websites. Thank you

1)

a. What are all the transversions that can be made starting with the codon CGG?

b. Which of these transversions will be missense? Can you be sure?

2) In mismatch repair in E. coli, only a mismatch in the newly synthesized strand is corrected. How is E. coli able to recognize the newly synthesized strand? Why does this ability make biological sense?

3) Why are many chemicals that test positive by the Ames test also classified as carcinogens?

4) What are bypass polymerases? How do they differ from the replicative polymerases? How do their special features facilitate their role in DNA repair?

5) Which repair pathway recognizes DNA damage during transcription? What happens if the damage is not repaired

6) Which of the following gene mutations is most likely to have the most severe impact on gene expression? Why?

A nonsense mutation in the last exon

A point mutation in an exon

A point mutation in the splice donor site of an intron

A point mutation in the middle of an intron

Answer 1

1) Transversion of CGG-

• CGG (arginine) can be become AGG (arginine), GGG (glycine), CCG (proline), CUG (leucine), CGC (arginine), or CGU (arginine).
• missense mutation is a point mutation in which a single nucleotide change results in a codon that codes for a different amino acid. in this case, transverions GGG, CCG, CUG will be missense.

2) The daughter polynucleotide is the newly synthesised strand that the error has occured; the parent polynucleotide has the correct sequence. Immediately after replication of methylated DNA, only the original parental strand carries the methyl groups, the two strands can be distinguished. In E.coli, the daughter strand, at this stage, undermethylated and can therefore can be distinguished from th parental polynucleotide, which has a full complemnt of methyl groups.

3) The Ames test is a method to test chemicals for their cancer causing properties. Ames test is based on the assumption that any substance that is mutagenic may also turn out to be carcinogenic, it may cause cancer. Most carcinogenic agents are also mutagenic.

5) During transcription the DNA damage is recognized by TC-NER(Transcription coupled - Nucleotide excision repair)  operates when damage to a transcribed DNA strand limits transcription activity. When the damage is unrecognized, the person suffers from Xeroderma pigmentosum and Cockayne syndrome. Individuals suffering from this autosomal recessive conditions are extremely sensitive to sunlight.

6) The correct answer is A point mutation in an exon.