Genetic Engineering MCQ – Restriction Endonuclease & Phosphatases – 1
Q.1 The restriction endonuclease is having a defence mechanism in the bacterial system against foreign DNA such as viruses. But how it is able to protect its own DNA?
A. By methylation of foreign DNA by restriction enzyme
B. By phosphorylation of foreign DNA by restriction enzyme
C. By methylation of bacterial DNA by restriction enzyme
D. By phosphorylation of bacterial DNA by restriction enzyme
Ans : By methylation of bacterial DNA by restriction enzyme
Q.2 The term ‘endonuclease’ refers to cutting the DNA sequence from ______________.
A. the ends of the chain
B. exactly in the middle of the chain
C. only within the polynucleotide chain, not at the ends
D. anywhere in the chain
Ans : only within the polynucleotide chain, not at the ends
Q.3 How many classes of restriction enzymes are there?
Ans : 3
Q.4 Even after replication, how the modified DNA remains protected?
A. It remains protected because of semi-conservative mode of replication
B. It is again modified after replication
C. It remains protected because of conservative mode of replication
D. The mode of replication has no role to play in the protection
Ans : It remains protected because of semi-conservative mode of replication
Q.5 After cleaving the sequence, the nature of the ends created by the type II endonuclease is __________.
A. The ends created are always double stranded
B. One end is single stranded and one end is double stranded
C. The ends created are always single stranded
D. Either the ends are single stranded or they are double stranded
Ans : Either the ends are single stranded or they are double stranded
Q.6 Type II cuts the sequence in the following way __________.
A. At 100-1000 nucleotides away from the recognition sequence
B. It cuts randomly
C. Within the recognition sequence
D. At 27-30 nucleotides away from the recognition sequence
Ans : Within the recognition sequence
Q.7 Blunt ends created by the restriction endonuclease can be joined.
Ans : True
Q.8 A sequence is having two ends, 5’ and 3’. Which of the following statements is correct regarding the nature of the ends?
A. The 5’ end is having phosphate group
B. Any group can be present at any end
C. The 5’ end is having hydroxyl group
D. The 3’ end is having phosphate group
Ans : The 5’ end is having phosphate group
Q.9 The recognition sequence of Sau3A is 5’ |GATC 3’ and that for DpnI is 5’ GA|TC 3’. Which of the statements is true?
A. The ends created by both the enzymes are not-compatible
B. The ends created by Sau3A are single stranded
C. The ends created by both the enzymes are compatible
D. The ends created by DpnI are single stranded
Ans : The ends created by both the enzymes are not-compatible
Q.10 The recognition sequence for BamHI is 5’ G|GATCC 3’. The ‘|’ represents the cutting site. What can be inferred about the ends from it?
A. The single stranded end is 5’ in nature
B. To decide about the nature of the ends more information is needed
C. The ends created are double stranded
D. The single stranded end is 3’ in nature
Ans : The single stranded end is 5’ in nature
Q.11 If all the nucleotides are present with equal frequencies and at random, what are the chances of having a particular four nucleotide long motif?
Ans : 1/256
Q.12 The recognition sequence is at times palindromic in nature. Which of the following statements is correct with respect to it?
A. When the molecules are cleaved by the same enzyme and the recognition sequence is palindromic in nature, there is no effect on annealing
B. The term ‘palindromic’ can be used whether the sequence is read from 5’ to 3’ or 3’ to 5’
C. The molecules which are cut by the same enzyme, anneal only if the sequence is palindromic in nature
D. There are increased chances of annealing if the recognition sequence is palindromic in nature
Ans : There are increased chances of annealing if the recognition sequence is palindromic in nature
Restriction Endonuclease & Phosphatases
- Definition: Restriction Endonucleases are enzymes that recognize specific DNA sequences and cleave the DNA at or near these sequences.
- Function: They play a crucial role in genetic engineering by allowing the precise cutting of DNA at specific sites, facilitating the manipulation of genetic material.
- Recognition Sequences: Each restriction endonuclease recognizes a specific DNA sequence, known as a recognition site or restriction site. These sites are usually palindromic, meaning they read the same backward as forward.
- Types: There are three main types of restriction endonucleases: Type I, Type II, and Type III. Type II restriction enzymes are the most commonly used in genetic engineering due to their simplicity and specificity.
- Applications: Used in recombinant DNA technology to create sticky ends or blunt ends, which are essential for DNA ligation and the construction of recombinant DNA molecules.
- Cloning Vectors: Restriction endonucleases are crucial in the creation of recombinant DNA vectors, where they help in inserting foreign DNA fragments into plasmids or other vectors.
- Molecular Scissors: Often referred to as “molecular scissors,” restriction endonucleases are fundamental tools for genetic engineers to manipulate and modify DNA.
- Definition: Phosphatases are enzymes that catalyze the removal of phosphate groups from molecules. In genetic engineering, they are particularly relevant in the context of DNA manipulation.
- Role in DNA Dephosphorylation: Phosphatases are used to dephosphorylate the 5′ ends of DNA molecules. This process is crucial before ligation reactions, as it prevents the self-ligation of DNA fragments.
- Preventing Self-Ligation: DNA fragments obtained by restriction enzyme digestion often have phosphate groups at their ends. Without dephosphorylation, these fragments could ligate back together, hindering the creation of recombinant DNA molecules.
- Facilitating Ligation: By removing the phosphate groups, phosphatases facilitate the subsequent ligation of DNA fragments. Ligation is a key step in creating recombinant DNA molecules.
- Applications: Phosphatases are commonly used in the preparation of DNA fragments for cloning, sequencing, and other molecular biology techniques.
- Types: Alkaline phosphatase and shrimp alkaline phosphatase are examples commonly employed in molecular biology applications.