Deck 14: Nucleic Acids

Question 1

Why do prokaryotes generally have no systems for direct control of protein synthesis?

Answer 1

The prokaryotes are the organisms which lack the membrane bound cell organelles and well defined nucleus. They carry out protein synthesis indirectly using their genetic material. In eukaryotes, the direct control of protein synthesis is in the hands of ribosome (protein factory). Since, the prokaryotes lack the same organelle (ribosomes) thus they cannot have direct control of protein synthesis.

Question 2

One way in which antibody diversity is achieved is through the enzyme cytidine deaminase, which removes the ammonia from a cytidine residue. To what base would the product of this reaction bind?

Answer 2

The cytidine molecule has the following structure from the after the removal of ammonia the structure formed is also mentioned below:
Thus, the molecule that will be formed after the removal of ammonia from the cytidine molecule is uracil. Since it is base of RNA (ribonucleic acid) it is then used for the synthesis of RNA molecule through transcription.

Question 3

Okasaki fragments must be joined by a ligase reaction. What would be the enzyme intermediate for this reaction?

Answer 3

The Okazaki fragments are those which are formed at the lagging strand of the DNA (deoxyribonucleic acid) during transcription. These fragments can be joined to form a new strand. This happens with the help of enzyme ligase which attaches the fragments first with a phosphate group. The reaction occurs as follows, and the enzyme intermediate is given below.

Question 4

Why are AT base pairs such as those present at the replication origins intrinsically weaker than GC base pairs?

Question 5

The lac operon, a model for transcription regulation, produces a single mRNA that codes for three proteins. Does this mean the rate of formation of all three proteins must be the same?

Question 6

What is the structural basis for the major and minor grooves in DNA?

Question 7

Most of the time, DNA exists as a double strand. Enumerate the circumstances under which it is a single strand.