BCH 5413 TEST BANK QUESTIONS WITH
VERIFIED ANSWERS FULL REVIEW
●● In mammilian DNA, which base has various forms
Answer: cytosine
●● Chargaff's rule
Answer: A=T and C=G
●● Is DNA conservative or semi-conservative?
Answer: semi-conservative
- parental sequence and daughter strand bind together
●● Alternative Double stranded DNA conformation
- A and Z DNA
Answer: A DNA
- dehydrated form
- right handed helix
- 11 bp per helical
- bp tilted 19 degrees
- major groove narrow and deep
- found with dsRNA and RNA-DNA duplex
,z-DNA
- >1% of cellular DNA
- favored by G-C repeats and alternating purines-pyrimidines
- left handed helix
- 12 bp per turn
- bp tilted 9 degrees
- major groove flattened, nearly gone
- bound by poxvirus E3L virulence factor and down regulates apoptosis
genes
●● Non-duplex DNA structures
- cruciform DNA
Answer: - inverted repeat sequence
- favored by excessive negative supercoiling
- AT-rich cruciforms associated with 'fragile' DNA
●● Alternative modes of base pairing
Answer: Watson Crick:
A--T and C---G
- adenine is at anti-conformation
,Hoogsteen:
- adenine or guanine can be flipped to sin-conformation (different H-
bonding)
●● Hoogsteen base pairing
- when can it occur
Answer: - in triplex and quadruplex DNA structures
●● Triplex DNA
Answer: - pyrimidine rich strand
- negative supercoiling
●● Chair DNA
Answer: - two G-rich strands
- down regulation of c-myc transcription
●● Intrinsic Bends in DNA
Answer: - distortion of the ideal B-DNA conformation resulting from
base stacking in the nucleotide sequence
Eg. Adenine-tract DNA results in 20 degree bends
- also can be found in duplex-oligonucleotide model DNA
- causes 23 degree bend and mis-stacking of one GC
, - DNA is not a uniform structure
●● Does B-DNA have a perfect structure?
Answer: No
- sequence specific local variation in twist between paired bases, sugat
conformation, tilt of base pairs, rise distance, etc.
●● Supercoiled DNA
- negative v. positive
Answer: - left handed under-twisted DNA is in a negative supercoil
- right handed over-twisted DNA is in a positive supercoil
*most is negatively supercoiled (topoisomerase releaves supercoiling)
●● Denaturation/Melting of DNA
Answer: - separation of DNA strands
- can happen due to temp, salt concentration, G---C content, and length
of DNA (Hyperchromicity effect)
- as temp increases, absorption of light increases due to bases becoming
less shielded when they melt apart
VERIFIED ANSWERS FULL REVIEW
●● In mammilian DNA, which base has various forms
Answer: cytosine
●● Chargaff's rule
Answer: A=T and C=G
●● Is DNA conservative or semi-conservative?
Answer: semi-conservative
- parental sequence and daughter strand bind together
●● Alternative Double stranded DNA conformation
- A and Z DNA
Answer: A DNA
- dehydrated form
- right handed helix
- 11 bp per helical
- bp tilted 19 degrees
- major groove narrow and deep
- found with dsRNA and RNA-DNA duplex
,z-DNA
- >1% of cellular DNA
- favored by G-C repeats and alternating purines-pyrimidines
- left handed helix
- 12 bp per turn
- bp tilted 9 degrees
- major groove flattened, nearly gone
- bound by poxvirus E3L virulence factor and down regulates apoptosis
genes
●● Non-duplex DNA structures
- cruciform DNA
Answer: - inverted repeat sequence
- favored by excessive negative supercoiling
- AT-rich cruciforms associated with 'fragile' DNA
●● Alternative modes of base pairing
Answer: Watson Crick:
A--T and C---G
- adenine is at anti-conformation
,Hoogsteen:
- adenine or guanine can be flipped to sin-conformation (different H-
bonding)
●● Hoogsteen base pairing
- when can it occur
Answer: - in triplex and quadruplex DNA structures
●● Triplex DNA
Answer: - pyrimidine rich strand
- negative supercoiling
●● Chair DNA
Answer: - two G-rich strands
- down regulation of c-myc transcription
●● Intrinsic Bends in DNA
Answer: - distortion of the ideal B-DNA conformation resulting from
base stacking in the nucleotide sequence
Eg. Adenine-tract DNA results in 20 degree bends
- also can be found in duplex-oligonucleotide model DNA
- causes 23 degree bend and mis-stacking of one GC
, - DNA is not a uniform structure
●● Does B-DNA have a perfect structure?
Answer: No
- sequence specific local variation in twist between paired bases, sugat
conformation, tilt of base pairs, rise distance, etc.
●● Supercoiled DNA
- negative v. positive
Answer: - left handed under-twisted DNA is in a negative supercoil
- right handed over-twisted DNA is in a positive supercoil
*most is negatively supercoiled (topoisomerase releaves supercoiling)
●● Denaturation/Melting of DNA
Answer: - separation of DNA strands
- can happen due to temp, salt concentration, G---C content, and length
of DNA (Hyperchromicity effect)
- as temp increases, absorption of light increases due to bases becoming
less shielded when they melt apart
