Question

5. About double strand DNA repair, it is correct to say that choose the most appropriate answer): 

(a) It requires one intact strand as a template for error correction. 

(b) Mismatches in the DNA are usually corrected via double strand DNA repair mechanisms. 

(c) Homologous recombination usually results in DNA repair with no loss of nucleotide at repair site. 

(d) Non-homologous end-joining usually results in DNA repair with no loss of nucleotide at repair site. 

6. A eukaryote gene has two introns and three exons. If the structure of the coding sequence is 5'3', answer the following questions: 

(a) What would the mature mRNA look like? 

(b) If the splice site of the 5' end of intron2 got mutated, so it was no longer recognized by the splicing machinery, what would the mature mRNA look like?

Answer 1

5) option a and c are most appropriate

A, It requires one intact stand as a template for error correction.

C, Homologus recombination usually results in DNA repair with no loss of nucleotide at repair site.

In cell double strand break ( DSB) appear in cell due to various external DNA damaging agent or during meiosis to carry out recombination. In DSB repair pathway , information of one intact stand is utilized to replac lost DNA fragments.

DSB can repair by homologus ( common in yeast)  or no homologous end joining method ( illegitimate method, error prone method ).

6) a) mature mRNA will contain exon1 -- exon 2-- exon 3 sequence

During splicing reaction, all the introns are removed and exons are ligated which form mature RNA. In case of normal splicing in a question all the 3 introns 1,w and 3 will be removed and exon 1 -- exon 2 will be present in functional mRNA.

B) in case of mutation of 5' splice site of intron 2 there will be skipping of exon 2 and mature mRNA will have

exon1- exon 3 in the mature mRNA.