This set of Molecular Biology Multiple Choice Questions & Answers (MCQs) focuses on “Site – Specific Recombination”.
1. How many classes of sequences are carried by recombination site?
Explanation: Recombination sites carry two classes of sequence elements. Sequences specifically bound by the recombinants and sequences where DNA cleavage and rejoining occur.
2. CSSSR can generate ____________ Different types of DNA rearrangement.
Explanation: CSSSR can generate three different types of DNA rearrangement.
i) Insertion of a segment of DNA into a specific site
ii) Deletion of a DNA segment
iii) Inversion of a DNA segment.
3. In recombinase recognition sequences what is the short sequence?
a) Crossover region
b) Cleavage region
c) Restriction region
d) Attachment region
Explanation: In the recombinase recognition sequences, the recognition sequence flank a central short asymmetric sequence known as the crossover region. In this site DNA cleavage and rejoining occur.
4. What are the two families of conservative site specific recombinases?
a) Alanine and phenylalanine
b) Threonine and valine
c) Arginine and lysine
d) Serine and tyrosine
Explanation: There are two families of conservative site specific recombinases, the serine and tyrosine recombinases. This mechanism is used when they cleave the DNA, a covalent protein-DNA intermediate is generated.
5. Site specific recombination is ATP dependent process.
Explanation: This process is required ATP hydrolysis. This process is needed for DNA cleavage and joining by the proteins.
6. What are the two proteins which creates site specific recombination?
a) DNA topoisomerases and Spo11
b) DNA gyrase
c) DNA ligase
d) DNA helicase
Explanation: Both DNA topoisomerases and Spo11 the protein that introduces double strand break into DNA. this initiates homologous recombination during meiosis.
7. How many single strands are generated during recombination?
Explanation: During recombination four single stranded DNA must be cleaved. They rejoined after the process with a different partner to generate the rearranged DNA.
8. Which recombinases cleaves the four strands before strand exchange occur?
Explanation: The serine recombinase cleaves all four strands before strand exchange occurs. One molecule of the recombinase protein promotes each of these cleavage reactions.
9. What is the correct pair of the four segments (R1, R2, R3, and R4)?
a) R2 and R3, R1 and R4
b) R2 and R1, R3 and R4
c) R1 and R2, R3 and R4
d) R1 and R3, R2 and R4
Explanation: For recombination to occur, the R2 segment of the Trp DNA molecule must recombine with R3 segment of the bottom DNA molecule. R1 segment of the top molecule must recombine with R4 segment of the bottom DNA molecule.
10. What is the nature of the DNA complex formed by the recombination process?
d) Non polar
Explanation: The structure of the DNA complex is hydrophobic. It provides little barrier to impede rotation of the top and bottom halves of the complex around each other.
11. How many mechanisms are involved in recombination process?
Explanation: Three mechanisms support the model of recombination:
i) DNA cleavage to form the covalent enzyme-DNA intermediate
ii) An 180˚ rotation of the dimmers in the protein-DNA complex
iii) Attack of the 3’-OH DNA ends on the resolvase DNA linkages.
12. How does tyrosine recombinase acts?
a) First join then cleave
b) First cleave then join
c) Both process occur simultaneously
d) Cleaves and rejoin two DNA pairs one after another
Explanation: The tyrosine recombinase cleaves and rejoins two DNA strands first and only then cleaves and rejoins the other two strands. The two DNA molecules with their recombination sites then align.
13. What is the enzyme involved in the tyrosine recombination process?
a) Cre recombinase
b) DNA polymerase
d) DNA recombinase
Explanation: In tyrosine recombinase, Cre recombinase is an example of the enzyme involved in the mechanism. This enzyme is encoded by phage P1 and acts by binding to to two different configurations of the recombining DNA.
14. What is the name of the site where Cre enzyme acts?
Explanation: The recombination site on the DNA where Cre acts are called the LOX site. Cre-LOX is a simple example of recombination by the tyrosine recombinase family.
15. What is the function of Salmonella Hix invertase?
a) Inversion of chromosomal region
b) Promotion of DNA deletion
c) Promotion of DNA integration
d) Promotion of base inversion
Explanation: It inverts a chromosomal region to flip a gene promoter by recognizing Hix sites. It allows expression of two distinct surface antigens.
Sanfoundry Global Education & Learning Series – Molecular Biology.
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