Lecture3: DNA Damage and Tools

Question 1

Mismatch

Answer 1

Errors in the replication process. Incorrect base pairing.

Question 2

Insertion

Answer 2

Insertion of (one or more) additional base pairs into the sequence

Question 3

Deletion

Answer 3

Deletion of (one or more) base pairs from the sequence

Question 4

Breaks + can cause (2)

Answer 4

Break in one or noth strands of the double helix. Can cause the DNA polymerase to stall or fall off during DNA replication.

Question 5

Mutagen + ex (2)

Answer 5

• Chemical agent that can alter specific bases within DNA
• Eg: Modification of DNA by epoxides (highly reactive), derived from chemicals in car exhaust, cigarette smoke, mold

Question 6

Reactive oxygen species such as hydroxyl radical causes …. + overall change

Answer 6

• oxidation of guanine to form 8-Oxoguanine which pairs with adenine instead of cytosine.
• Overall change is G-C to T-A

Question 7

Mismatch repair (3)

Answer 7

1. MutS/MutL detects mismatch
2. MutH endonuclease makes an internal cut. Exonuclease removes part of the strand containing the error.
3. Gap is filled by DNA polymerase 3 and sealed by DNA ligase with ATP

Question 8

Plasmid (2)

What are they+ they can replicated

Answer 8

• Small, circular double stranded DNA molecule seperated from the chromosomal DNA
• Can replicate independently

Question 9

Most mismatch errors are repaired by+ the process

Answer 9

• DNA polymerase through proofreading
• 3’-5’ exonuclease activity: Polymerase workds backwards to excise an incorrect base at the end of the growing DNA chain

Question 10

Mistakes that escape proofreading are normally corrected by

Answer 10

additional DNA repair mechanisms

Question 11

Deamination (4)

what happens+ which bases+ deamination of adenine forms+overall result

Answer 11

• hydrolytic removal of an amino group
• cytosine, adenine and guanine contains amino groups
• Deamination of adenine froms hypoxanthine which pairs with cytosine.
• Overall result: A-T changed to G-C

Question 12

Palindromic

Answer 12

The same sequence is read on each strand 5’-3’

Question 13

Restriction enzymes (2)

originally+cleaves

Answer 13

• Enzymes originally isolated from bacteria where they cut up invading bacteriophage DNA
• Cleaves phosphodiester bonds between nucleotides at specific DNA sequences on both strands