DNA Damage + Repair

Question 1

DNA Damage vs DNA Mutation

Answer 1

• DNA damage is an abnormal chemical structure found in the DNA, changing the structure of the genetic material + prevents replication mechanism from functioning properly
• DNA mutation is a change in the sequence of standard base pairs

Question 2

Sources of DNA damage

Answer 2

• Spontaneous replication or chemical damage
• Chemically induced damage
• Radiation

Question 3

Spontaneous Replication Damage

Answer 3

• DNA/Genetic insults caused by process of DNA replication during cell division
• The rate at which DNAP adds incorrect nucleotides determines spontaneous mutation rate in an organism
• Includes Tautomeric shifts

Question 4

Spontaneous Chemical Damage

Answer 4

• Includes:
  + Depurination
  + Deamination

Question 5

Chemically Induced Mutations

Answer 5

• Often caused by base analogs, where they are similar in structure to the original DNA bases ie 5-Bromouracil which is similar to thymine
• Some mutagens include:
  + Alkylating agents
  + Nitrous acid
  + Hydroxylamine
• Further includes Oxidative reactions + Intercalating agents

Question 6

DNA wobble

Answer 6

A base pairing between 2 nucleotides in RNA that don’t follow the standard (Watson-Crick) base pairing rules

Question 7

DNA damage in non-replicating + replicating cells

Answer 7

• Most DNA damages can undergo DNA repair, but repair isn’t 100% efficient
• Unrepaired DNA damages accumulate in non-replicating cells ie brain cells, muscle cells etc and as a result causes aging
• In replicating cells, errors occur upon replication past damages in the template strand of DNA/ during repair of DNA damages, giving rise to mutations/epigenetic alterations

Question 8

Types of Repair pathways

Answer 8

• Nucleotide Excision Repair (NER)
• Base Excision Repair )BER)
• Double-Strand Break Repair (DSBR)
• Mismatch Repair (MMR)

Question 9

Transition

Answer 9

Interchanges of 2-ring purines (A,G) or of 1-ring pyrimidines (C,T) ie Adenine changed for Guanine

Question 10

Transversion

Answer 10

A point mutation in DNA which a single purine is changed for a pyrimidine or vice versa. Can be spontaneous or caused by ionising radiation/alkylating agents