Question

21. In DNA replication, new nucleotides are added a. To the 5' end of each nascent strand b. To the 3'end of each nascent strand To both ends of each nascent strand d. To the 5' end of the continuous strand and the 3' end of the discontinuous strand e. To the end of the continuous strand and the end of discontinuous strand fragments 22. DNA unwinding is done by a. Ligase b. Helicase c. Topoisomerase dHexonuclease 23. Proofreading of newly synthesized DNA is done by a. DNA ligase 9. Hydrogenase Gyrase d. DNA polymerase 24. Proofreading and repair occur a. At anytime during and after synthesis of DNA b. Only before DNA synthesis C. Only in the presence of DNA polymerase Only in the presence of an excision repair mechanism 25. In humans, DNA double-strand breaks may be repaired by a. Mismatch repair b. Base excision repair C. Nucleotide excision repair d. Nonhomologous end joining Restriction enzymes are enzymes a. Capable of cutting DNA molecule b. Capable of adding nucleotides to the 3'-OH end C. Capable of restriction protein synthesize d. Capable of joining DNA molecules

Answer 1

21. Answer : e ; To the 3' end of the continuous strand and 5' end of the discontinuous strand fragments.

Explanation : We all know that DNA replication occurs towards the 5' to 3' end. So,in that case new nucleotides are added to the 3' end of the continuous strand and 5' end of the discontinuous strand fragments.

22. Answer ; b ; Helicase.

Explanation : DNA helicase is the enzyme that unwinds the DNA double helix by breaking the hydrogen bonds down the center of the strand.

23. Answer : d ; DNA polymerase.

Explanation : DNA polymerases are the enzymes that build DNA in cells. During DNA replication, most DNA polymerases can check their work with each base that they add. This process is called proofreading. DNA Polymerase uses 3' to 5' exonuclease activity to remove the incorrect nucleotides from the 3' end of the new strand.

24. Answer : c ; Only the presence of DNA polymerase

Explanation : DNA polymerases are the enzymes that build DNA in cells. During DNA replication, most DNA polymerases can check their work with each base that they add. This process is called proofreading. DNA Polymerase uses 3' to 5' exonuclease activity to remove the incorrect nucleotides from the 3' end of the new strand.

25. Answer : d ; Non-homologous and joining.

Explanation : In humans DNA double strand breaks can be repaired by the non-homologous end joining (NHEJ) pathway. NHEJ is a process by which the cell can repair strand breaks without the need for a homologous template. NHEJ often leads to insertions or deletions of nucleotides at the site of repair.

26. Answer : a ; Capable of cutting DNA molecules.

Explanation : A restriction enzyme is a protein that recognizes a specific, short nucleotide sequence and cuts the DNA only at that specific site.