1. Which enzyme covalently joins two DNA fragments during recombinant DNA formation?
A.
DNA ligase
B.
Restriction endonuclease
C.
DNA helicase
D.
RNA polymerase
Correct Answer:
DNA ligase
Explanation:
DNA ligase joins DNA fragments by forming covalent bonds between their sugar-phosphate backbones.
2. What type of covalent bond is formed when DNA fragments are joined by DNA ligase?
A.
Peptide bond
B.
Phosphodiester bond
C.
Hydrogen bond
D.
Glycosidic bond
Correct Answer:
Phosphodiester bond
Explanation:
DNA ligase forms phosphodiester bonds between adjacent nucleotides in the DNA sugar-phosphate backbone.
3. The covalent joining of an inserted DNA fragment to a vector is called
A.
Ligation
B.
Replication
C.
Transcription
D.
Translation
Correct Answer:
Ligation
Explanation:
Ligation is the process in which DNA ligase covalently joins the insert DNA and vector DNA.
4. DNA ligase mainly joins the ______ of two DNA fragments.
A.
Sugar-phosphate backbones
B.
Nitrogenous bases only
C.
Amino acid chains
D.
RNA primers only
Correct Answer:
Sugar-phosphate backbones
Explanation:
During covalent joining, DNA ligase seals breaks in the sugar-phosphate backbones of DNA fragments.
5. Which type of DNA ends can be covalently joined by DNA ligase after proper alignment?
A.
Compatible sticky ends
B.
Unrelated protein ends
C.
Lipid ends
D.
Amino acid ends
Correct Answer:
Compatible sticky ends
Explanation:
Compatible sticky ends can base-pair with each other, allowing DNA ligase to form covalent phosphodiester bonds.
6. What is the main role of DNA ligase in recombinant DNA technology?
A.
To seal nicks between joined DNA fragments
B.
To cut DNA at specific sequences
C.
To unwind the DNA double helix
D.
To produce messenger RNA
Correct Answer:
To seal nicks between joined DNA fragments
Explanation:
DNA ligase seals breaks or nicks in the sugar-phosphate backbone after DNA fragments have been aligned.
7. Which structure is restored when DNA ligase covalently joins two DNA fragments?
A.
A continuous sugar-phosphate backbone
B.
A protein backbone
C.
A carbohydrate capsule
D.
A membrane bilayer
Correct Answer:
A continuous sugar-phosphate backbone
Explanation:
DNA ligase connects adjacent nucleotides so that the separate DNA fragments become part of one continuous backbone.
8. Before DNA ligase can covalently join compatible DNA ends, the ends usually need to
A.
Base-pair with each other
B.
Be converted into proteins
C.
Lose all their nucleotides
D.
Separate into amino acids
Correct Answer:
Base-pair with each other
Explanation:
Compatible ends first align through complementary base pairing, enabling DNA ligase to seal the backbones covalently.
9. Which statement correctly describes the product of DNA ligation?
A.
Two DNA fragments become covalently connected
B.
DNA is changed into RNA
C.
Proteins are broken into nucleotides
D.
DNA strands are permanently separated
Correct Answer:
Two DNA fragments become covalently connected
Explanation:
Ligation produces a single joined DNA molecule by forming covalent phosphodiester bonds between DNA fragments.
10. In recombinant DNA technology, DNA ligase is used after DNA fragments have been
A.
Placed together with compatible ends
B.
Translated into proteins
C.
Converted into lipids
D.
Destroyed by heat
Correct Answer:
Placed together with compatible ends
Explanation:
DNA ligase acts after compatible DNA ends are brought together and aligned, sealing them through covalent phosphodiester bonds.
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