This set of Molecular Biology Multiple Choice Questions & Answers (MCQs) focuses on “Site-Directed Mutagenesis & Overview of Recombination”.
1. Which of the following properties is improved by site directed mutagenesis?
a) Physical property
b) Chemical property
c) Kinetic property
Explanation: Site directed mutagenesis is a process used to achieve protein engineering. Protein engineering improves the kinetic property of the protein by altering the amino acid structure and sequence.
2. What is the formula for annealing temperature for polymerase chain reaction primer?
a) Tm = 81.5 + 0.41 (%AT) – (675/N)
b) Tm = 81.5 + 0.41 (%GC) – (675/N)
c) Tm = 81.2 + 0.41 (%GC) – (672/N)
d) Tm = 81.5 + 0.42 (%AT) – (675/N)
Explanation: For calculating the annealing temperature for a PCR primer is Tm = 81.5 + 0.41 (%GC) – (675/N). Here the % of GC is the total amount of G and C present in the oligonucleotide primer and the target of interested and N is the length of the oligonucleotide primer.
3. What is the function of Dpm I endonuclease in Tm method of site directed mutagenesis?
a) Joining of blunt ends
b) Addition of dNTPs
c) Sensitive to cleavage of methylated DNA
d) Breaking of DNA strand
Explanation: In Tm method the template DNA was deprived from an E. coli cell with an intact restriction modification system. This strand is sensitive to restriction by the Dpn I endonuclease.
4. Which phage is used in oligonucleotide directed mutagenesis?
d) λ – phage
Explanation: M13 phage is single stranded phage. It is used for cloning a specific DNA sequence which will be mutated.
5. Write down the name of scientist who has discovered the method of site directed mutagenesis?
a) Bostein Shortle
d) Joller Smith
Explanation: In 1985 Joller Smith discovered site directed mutagenesis technique. By this technique the nucleotide sequence of a cloned DNA fragment may be changed by site directed mutagenesis using synthetic oligonucleotide.
6. Which two genes are absent in the E. coli strain CJ236?
Explanation: CJ236 which lacks functional dut-phase and uracil N-glycosylase. These are used for generating uracilated single stranded DNA.
7. Which polymerase is used in PCR based mutagenesis?
a) Deep vent R polymerase
b) pfu polymerase
c) Taq polymerase
d) DNA polymerase
Explanation: In PCR based mutagenesis pfu polymerase is used. After 12 – 15 cycles of amplification new strands will be generated.
8. Homologous recombination in germ cells occur in the ____________ phase.
Explanation: Homologous recombination in germ cells occurs in the pachytene phase of meiosis I. This exchange is classically termed as crossing over and occurs via the formation of a synaptonemal complex between the two homologous chromosomes.
9. The frequency of crossing over between two genes on a same chromosome is independent of their position.
Explanation: The frequency of crossing over between two genes on a same chromosome is dependent of their locus. The more distance between the two genes the more will be the probability of recombination.
10. When two genes on a chromosome is inherited without any record of recombination the genes are said to be ____________
Explanation: When two genes on a chromosome is inherited without any record of recombination the genes are said to be linked. This is because they are placed so close together that no recombination is able to take place. The phenomenon is known as linkage.
11. Homologous recombination does not provide ____________
a) Genetic variation
b) Sequence retrieval
c) Restart of stalled replication
d) Random base incorporation
Explanation: The homologous recombination provides three functions:
i) Provides genetic variation
ii) Allows the retrieval of sequences lost through DNA damage
iii) Provides mechanism for restarting stalled or damaged replication forks.
12. Recombination regulates the function of genes.
Explanation: Special types of recombination regulate the expression of some genes. For example by switching specific segments within chromosomes, cells can put otherwise dormant genes into sites where they are expressed.
13. What is strand invasion?
a) Fork collapse
b) Nick in template strand
c) Formation of lesion
d) Complementary strand pairing
Explanation: The pairing between short regions occurs when a single stranded region of DNA originating from one molecule with its complementary strand in the homologous DNA duplex. This event is known as the strand invasion process.
14. What is holiday junction?
a) The site of strand break
b) The site of heteroduplex DNA formation
c) Formation of a crossing over complex
d) The site of strand invasion
Explanation: After strand invasion, the two DNA molecules become connected by crossing over of DNA strands. It forms a structure called the Holiday junction.
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