Question

1. (a) Assume that during DNA replication in a bacterium a mistake is made and a G is inserted into the newly synthesized DNA strand opposite a T in the template DNA strand. If this mistake is not repaired before the next round of DNA replication, what mutation will eventually result? Show your work (b) What type of mutation is the resulting mutation? (transversion, transition, indel, base substitution) 2. (a) What is the purpose of Taq polymerase in a PCR reaction? (DNA denaturation, primer annealing, DNA synthesis, heating of the reaction, heating of the reaction and DNA denaturation, Energy (b) Explain your choice:

Answer 1

Answer 1:(a) When G is inserted mistakenly opposite to T, Let’s take an example:

Suppose the sequence is,

AACCTT…

TTGGGA …

Explanation:

The mutation occurred in which G is inserted in the new template instead of A which is opposite to T, this caused transition mutation as purine is inserted in place of purine i.e., (A ↔ G). However, the correct sequence without any error would be this:

AACCTT…

TTGGAA …

So, clearly this error or mistake that occurred due to mismatching of pair G opposite to A resulted in transition mutation (in which a purine is replaced with purine i.e., (A ↔ G) and Pyrimidine with pyrimidine i.e. (C ↔ T))

If this gets replicated and it is not corrected before replication it will become a permanent mutation after the next cell division. These replications along with mutations happening further incorrectly, Will make new sequences that will serve as templates for next replication and will again cause mismatching or all other future replications will go wrong. For example:

AACCTT… (Template strand)

TTGGGA … (New strand)

AACCCT … (coding strand)

TTGGGU…. (New mRNA strand)

AACCCT… (template strand)

In case of if no changes occurred or no mistake might have happened it would have been:

AACCTT… (Template strand)

TTGGAA … (New strand)

AACCTT… (coding strand)

TTGGUU… (New mRNA strand)

AACCAA… (template strand)

All this happens according to the semi-conservative principle of replication in which during every DNA replication, each new double-strand serves as the template strands for another round of replication. This consists of one parental strand and one new daughter strand.

Answer 1(b) The resulted mutation is the transversion mutation as A must be formed but instead, C is formed which shows Purine is replaced by pyrimidine.

i.e. AACCCT… (template strand) formed this instead of AACCAA.

Answer 2 (a)

The purpose of Taq DNA polymerase is that it is a heat-tolerant or thermostable enzyme and this can work for the very first step of PCR reaction in which denaturation at high temperature takes place. The Polymerase chain reaction aims at amplifying or making multiple copies of the target DNA.

Answer 2 ( b)

Denaturation: This is the first step in the PCR reaction in which DNA is melted with the help of an enzyme called Taq polymerase . It is a heat-tolerant enzyme that remains functional at this high temperature ranging from 92 to 94 degrees celsius

The next 2 steps in the PCR are annealing and extension.