drexel bio 209 final Exam | Most
Recent Exam 2026 Actual
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What non-chemical mutagenic agents exist? - ANSWER-UV
radiation
-Pyrimidines and Purines absorb max at 254 nm
-Max. mutation at 254nm
-UV "excites" bases causing pyrimidine dimers and pyrimidine
hydrates
What is the mechanism of DNA recombination? - ANSWER-
•Recombination of
homologous
chromosomes
-Crossing over during prophase of the first
meiotic division
•A number of repair enzymes
involved
-E. coli Rec genes
involved
•Cleave single
strand
,•Helicase
activity
•Promote single strand
exchange
•DNA
ligase
How do defects in DNA repair contribute to human disease? -
ANSWER-
•Repair systems essential
•Numerous disease associated with defective DNA repair
•Xeroderma pigmentosum (XP)
-1/250,000; autosomal recessive
•Phenotype: extreme sensitivity to sunlight, intense freckling,
skin cancer -Results from defects in nine different genes
•Six of these nine involved nucleotide excision repair,
specifically exinuclease activity
Human Diseases with defects in repair - ANSWER-
•Cockayne Syndrome
-Defects in nucleotide excision
repair
-Retarded growth, diminished mental
skills
-No increase in skin
cancer
•Trichothiodystrophy
-Defects in nucleotide excision repair
-Short stature, brittle hair, scaly scalp, diminished mental skills
,•Others
-Ataxia telanglectasica
-Fanconi Anemia
Bloom Syndrome
DNA polymerase1 not required for growth - ANSWER-
mutant of pol A
- lacks 5' to 3' polymerase
activity
ecoli still viable, DNA pol not responsible for
replication of E coli
sensitive to UV
light
DNA ligase - ANSWER-catalyzes the covalent closure of
nicks in DNA link okazaki fragments requires ATP or
NAD
doesnt fill gaps where bases are missing
priming new DNA synthesis - ANSWER-can be
random DNA enzyme can produce DNA primer
enzyme could produce RNA primer RNA
polymerase doesnt require primers
DNA primase requires inly a DNA template
unwinding DNA - ANSWER-DNA helicase unwinds DNA using
ATP
DNA must be rotated 360 for every 10 bp
helicases possess 6 subunits
, - produce two single strand of DNA to be replicated
single stran DNA binding protien keeps single strand of DNA
extends
Supercoiling - ANSWER-positive-
overwound tight DNA
negative- unwound
relaxed DNA
topoisimerases- 1
and2
Topoisomerases - ANSWER-All living things have
topoisomerases
Type 1 does single stranded breaks and rotates the DNA to
relieve tension Type 2 (ex. DNA gyrase) breaks both strands
and rotates the DNA to relieve tension (transient and stable
process), takes overwound supercoils and loops it through one
of the breaks
Base Excision Repair - ANSWER-•Prokaryotes and
Eukaryotes
•Removes abnormal or chemically
modified bases
•Specific glycosylases recognize specific
base alterations
1.Glycosylases mediated base removal (AP
site created)
2.AP endonuclease removes
backbone
Recent Exam 2026 Actual
Complete Real Exam Questions
And Correct Answers (Verified
Answers) Already Graded A+ |
Guaranteed Success!! Newest
Exam | Just Released!!
What non-chemical mutagenic agents exist? - ANSWER-UV
radiation
-Pyrimidines and Purines absorb max at 254 nm
-Max. mutation at 254nm
-UV "excites" bases causing pyrimidine dimers and pyrimidine
hydrates
What is the mechanism of DNA recombination? - ANSWER-
•Recombination of
homologous
chromosomes
-Crossing over during prophase of the first
meiotic division
•A number of repair enzymes
involved
-E. coli Rec genes
involved
•Cleave single
strand
,•Helicase
activity
•Promote single strand
exchange
•DNA
ligase
How do defects in DNA repair contribute to human disease? -
ANSWER-
•Repair systems essential
•Numerous disease associated with defective DNA repair
•Xeroderma pigmentosum (XP)
-1/250,000; autosomal recessive
•Phenotype: extreme sensitivity to sunlight, intense freckling,
skin cancer -Results from defects in nine different genes
•Six of these nine involved nucleotide excision repair,
specifically exinuclease activity
Human Diseases with defects in repair - ANSWER-
•Cockayne Syndrome
-Defects in nucleotide excision
repair
-Retarded growth, diminished mental
skills
-No increase in skin
cancer
•Trichothiodystrophy
-Defects in nucleotide excision repair
-Short stature, brittle hair, scaly scalp, diminished mental skills
,•Others
-Ataxia telanglectasica
-Fanconi Anemia
Bloom Syndrome
DNA polymerase1 not required for growth - ANSWER-
mutant of pol A
- lacks 5' to 3' polymerase
activity
ecoli still viable, DNA pol not responsible for
replication of E coli
sensitive to UV
light
DNA ligase - ANSWER-catalyzes the covalent closure of
nicks in DNA link okazaki fragments requires ATP or
NAD
doesnt fill gaps where bases are missing
priming new DNA synthesis - ANSWER-can be
random DNA enzyme can produce DNA primer
enzyme could produce RNA primer RNA
polymerase doesnt require primers
DNA primase requires inly a DNA template
unwinding DNA - ANSWER-DNA helicase unwinds DNA using
ATP
DNA must be rotated 360 for every 10 bp
helicases possess 6 subunits
, - produce two single strand of DNA to be replicated
single stran DNA binding protien keeps single strand of DNA
extends
Supercoiling - ANSWER-positive-
overwound tight DNA
negative- unwound
relaxed DNA
topoisimerases- 1
and2
Topoisomerases - ANSWER-All living things have
topoisomerases
Type 1 does single stranded breaks and rotates the DNA to
relieve tension Type 2 (ex. DNA gyrase) breaks both strands
and rotates the DNA to relieve tension (transient and stable
process), takes overwound supercoils and loops it through one
of the breaks
Base Excision Repair - ANSWER-•Prokaryotes and
Eukaryotes
•Removes abnormal or chemically
modified bases
•Specific glycosylases recognize specific
base alterations
1.Glycosylases mediated base removal (AP
site created)
2.AP endonuclease removes
backbone
