Questions and Correct
Answers | New Update
DNA structure - ANSWER ✔✔- nucleic acid bases (purine (A,G) and
pyrimidine (C,U,T))
- sugars (ribose, deoxyribose)
- sugars linked by phosphate groups (sugar-phosphate backbone)
*form antiparallel strands
,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)
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, 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.