Bch 5413 Exam 4: DNA Repair and Cell Cycle
Questions and Correct Answers (Verified
Answers) | Graded A+ | Latest Update 2025-2026
How do mutations occur? - ANSWERS replication errors and DNA damage
Why does DNA need to be repaired compared to RNA or proteins? - ANSWERS
RNA and proteins can be replaced by the information encoded by the DNA - DNA
itself can't be replaced by a new DNA when it gets damaged, thus it requires
repair
List endogeous and exogenous sources of DNA damage: - ANSWERS
endogenous (cellular processes) - oxidation, alkylation, or hydrolysis of DNA
bases; bulky adduct formation; mismatch of bases due to errers in DNA replication
exogenous (environment, radiation, oxidative stress) - UV, X-ray; ionozing
radiation; industrial chemicals; even oxygen
What is DNA damage? - ANSWERS a chemical alteration to DNA
Common examples of DNA damage: - ANSWERS replication errors, base
modifications caused by spontaneous DNA damage, DNA alkylation, oxidatvie DNA
damage, pyriidine dimers caused by UV radiation, DNA strand breaks by ionizing
radiation
What happens with DNA mismatches? - ANSWERS Hydrogen-bonding
properties of Watson-Crick base pair bonding mismatches
, G:T instead of G:C
G:A instead of T:A
DNA mismatches consisting of chemically regular DNA bases must be considered
pro-mutagenic DNA aberrations
What happens during deamination? - ANSWERS deamination (removal of an
amino group): generates mutagenic lesians such as uracil (deaminated cytosine),
hypoxanthine (deaminated adenine), and xanthine (deaminated guanine)
What happens in depurination? - ANSWERS depurination (loss of purine):
hyrolysis of the N-b-glycosyl bond linking a purine base to the sugar-phosphate
backbone; elevated temperature increases the rate of depurination
guanine residue --H2O--> guanine + apurinic residue
What happens in alkylation of bases? - ANSWERS DNA alkylation is a process
where electrophilic substances (electrophiles):
1. seek negative centers in DNA
2. attack them
3. add carbon-contiaining groups (alkyl groups)
Most commonly attacked targets of alkylation are phosphodiester bonds
Alkylating agents such as carcinogens can add alkyl groups to DNA bases
Questions and Correct Answers (Verified
Answers) | Graded A+ | Latest Update 2025-2026
How do mutations occur? - ANSWERS replication errors and DNA damage
Why does DNA need to be repaired compared to RNA or proteins? - ANSWERS
RNA and proteins can be replaced by the information encoded by the DNA - DNA
itself can't be replaced by a new DNA when it gets damaged, thus it requires
repair
List endogeous and exogenous sources of DNA damage: - ANSWERS
endogenous (cellular processes) - oxidation, alkylation, or hydrolysis of DNA
bases; bulky adduct formation; mismatch of bases due to errers in DNA replication
exogenous (environment, radiation, oxidative stress) - UV, X-ray; ionozing
radiation; industrial chemicals; even oxygen
What is DNA damage? - ANSWERS a chemical alteration to DNA
Common examples of DNA damage: - ANSWERS replication errors, base
modifications caused by spontaneous DNA damage, DNA alkylation, oxidatvie DNA
damage, pyriidine dimers caused by UV radiation, DNA strand breaks by ionizing
radiation
What happens with DNA mismatches? - ANSWERS Hydrogen-bonding
properties of Watson-Crick base pair bonding mismatches
, G:T instead of G:C
G:A instead of T:A
DNA mismatches consisting of chemically regular DNA bases must be considered
pro-mutagenic DNA aberrations
What happens during deamination? - ANSWERS deamination (removal of an
amino group): generates mutagenic lesians such as uracil (deaminated cytosine),
hypoxanthine (deaminated adenine), and xanthine (deaminated guanine)
What happens in depurination? - ANSWERS depurination (loss of purine):
hyrolysis of the N-b-glycosyl bond linking a purine base to the sugar-phosphate
backbone; elevated temperature increases the rate of depurination
guanine residue --H2O--> guanine + apurinic residue
What happens in alkylation of bases? - ANSWERS DNA alkylation is a process
where electrophilic substances (electrophiles):
1. seek negative centers in DNA
2. attack them
3. add carbon-contiaining groups (alkyl groups)
Most commonly attacked targets of alkylation are phosphodiester bonds
Alkylating agents such as carcinogens can add alkyl groups to DNA bases
