Study Questions Set 5

Question 1

Distinguish between the terms “mutation”, “DNA repair” and “recombination”.

Answer 1

• Mutation: a permanent change in DNA caused when DNA fails to get repaired prior to the next round of replication
• DNA Repair: the processes in which a cell identifies and corrects any damage to the DNA molecule
• Recombination: an exchange of genetic material between two DNA molecules – causes DNA rearrangement

Question 2

Explain how errors in DNA replication can lead to mutations.

Answer 2

• If one base pair is wrong, that can lead to a different amino acid being coded, which could cause a malfunctioning protein, which would lead to a mutation

Question 3

List the 3 major causes of mutation in DNA

Answer 3

• Replication errors: mistakes made during replication that weren’t detected and repaired by DNAP/III
• Spontaneous changes in DNA: depurinations and spontaneous daminations of C into U
• External factors: radiation, temp change, mutagens etc.

Question 4

Distinguish between the effects of mutations on the somatic and germ cells of multicellular organism.

Answer 4

• If the mutation occurs in a germ cell, the disease can becomes hereditary
• If the mutation occurs in a somatic cell, the disease is non-hereditary

Question 5

List the various types of DNA repair mechanism (we have mentioned seven).

Answer 5

• Proof-reading or editing by DNA polymerase
• Mismatch repair – corrects errors during replication not caught by DNAP
• Direct reversal of damage:
o Photolyase breaks covalent T-T bonds that are caused by UV light
o De-methylation of O6-G to return to normal form
• Excision repairs:
o Base excision repair – damaged base removed from backbone by lesion specific DNA glycosylases
o Nucleotide excision repair – removal and replacement of ss fragment, not lesion-specific, cleaves on both sides of the damage
• Repair Double-Strand Breaks (DSBs):
o Recombination repair – activated when both strands are effected: either replication fork damage or damage at the same place in both strands
o Error prone repairs:
 Nonhomologous end joining – when both strands are broken simultaneous; protein complex joins them together again, some genetic material is lost
 SOS translesion repair – polymerases add nucleotides randomly

Question 6

What are biological roles of DNA recombination?

Answer 6

• DNA repair
• Creation of new gene/allele combinations
• Formation of new genes
• Integration of a specific DNA element

Question 7

List and briefly describe the ways genomic DNA can be rearranged (there are three of them).

Answer 7

• General or homologous recombination: exchange between a pair of homologous DNA sequences
• Site-specific recombination: between sequences with a limited stretch of similarly
• Transposition: mobile DNA elements that move from the donor to the target site