Question

16) Answer the following multiple-choice questions about genetics:

1. Which activity of E. coli DNA polymerase I is responsible for proofreading the newly synthesized DNA?

A. 5' to 3' exonuclease

B. 3' to 5' endonuclease

C. 5' to 3' polymerase

D. 3' to 5' exonuclease

E. none of the above

2. DNA sample A melts or denatures into two separate strands at a lower temperature than DNA sample B. Why is this so?

A. sample A has greater G-C bp than sample B

B. sample A has greater A-T bp than sample B

C. sample A is from a prokaryote and sample B is from a eukaryote

D. sample A is from a bacteria and sample B is from a virus

E. none of the above

3. Which cluster of terms accurately reflects the nature of DNA replication in prokaryotes?

A. random point of initiation, bidirectional, semi-conservative

B. fixed point of initiation, bidirectional, conservative

C. fixed point of initiation, unidirectional, conservative

D. random point of initiation, unidirectional, semi-conservative

E. fixed point of initiation, bidirectional, semi-conservative

4. Which DNA will have the highest density given the following G+C/A+T ratios?

A. 1/5

B. 2/1

C. 1/1

D. 9/1

E. 3/2

Please answer all parts and be sure to circle final answers or make them obvious amongst work and explanations

Answer 1

Ansi)D) 3' to 5' exonuclease activity

Explaination:

3'to 5' exonuclease activity of polymerase I is responsible for proof reading.

5' to 3' exonuclease activity of pol I is responsible for removal of RNA primer.

3' to 5' endonuclease activity is property of endonucleases not of polymerase.

5' to 3' polymerase activity of Pol I is responsible for phosphodiester bond formation.

Ansii) B)sample A has greater A-T bp than sample B

Explaination: More the GC content more will be melting temperarure hence sample A has more A-T content and less GC content as compare to sample B so it require low melting temperature for denaturation as compare to sample B.

Ansiii) E. fixed point of initiation, bidirectional, semi-conservative

Explaination: Bacterial chromosome is circular so they have single origin of replication where replication starts so it is a fixed point, bacterial replication is bidirectional and semi conservative in nature as in daughter DNA helix on strand is parental while second one is newly synthesized daughter strand.

Ansiv) d) 9/1

Explaiantion: Higher the GC content higher will be density of DNA so DNA with G+C/A+T =9/1 in all options is maximum denser.