FRNSC 420 - EXAM 2 PRACTICE QUESTIONS AND ANSWERS (100% PASS)
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Course
FRNSC421W /FRNSC 420
Institution
FRNSC421W /FRNSC 420
FRNSC 420 - EXAM 2 PRACTICE QUESTIONS AND
ANSWERS (100% PASS)
nucleosome assembly/reassembly after replication - Answer️️ -- old H3-H4
tetramers remain bound to one of two daughter duplexes at random
- old H2A-H2B dimers dissociate and compete to associate with tetramers
- DNA sliding clam...
replication fork - Answer✔️✔️-Y-shaped region that directs synthesis, allows for
synthesis of two strands at once
- continuous replication of the leading strand towards the fork
- discontinuous replication of the lagging strand using Okazaki fragments away
from the fork
driving force of DNA synthesis - Answer✔️✔️-the free energy of nucleotide
addition is low, but when coupled with the hydrolysis of pyrophosphate (PPi), the
reaction is favored
- initiation is an SN2 reaction with 3'-OH acting as nucleophile to attack the α-
phosphate of incoming dNTP
- extension of primer 3' end by one nucleotide and release of PPi
- PPi is hydrolyzed by pyrophosphatase to yield two inorganic phosphate (Pi)
molecules
3-D structure of DNA polymerase - Answer✔️✔️-like a cupped right hand with
palm, fingers, and thumb
- palm: a β-sheet holding active site. binds metal (Mg or Zn) to initiate synthesis
and monitors base pairing through H-bond contacts with minor groove. allows for
proofreading, will release primer at a mismatch
- fingers: α-helices that act in positioning nucleotides, pushing active site
components together. Arg and Lys residues form electrostatic interactions to
ensure proper orientation; Tyr residues base stack for stability. also can bend the
backbone to expose first template base
- thumb: α-helices that maintain correct positioning of primer and active site.
maintains association between polymerase and template. works in concert w/ palm
to move synthesized DNA from active site, contributes to processivity
physical ways DNA polymerase maintains fidelity - Answer✔️✔️-active site has
discriminator site of neutral, nonpolar, and aromatic amino acids that can
differentiate between NTPs and dNTPs
- normally, AAs interact w/ ribose ring and 3'-OH of neighboring base pair attack
phosphate group of incoming nucleotide
- activity is blocked with 2'-OH group in NTPs due to steric hinderance; base will
tilt and not be recognized by neighbor 3'-OH
- dNTP binding pocket is small, most other ribonucleotides wont fit
enzymatic ways DNA polymerase maintains fidelity - Answer✔️✔️-a 3' to 5'
exonuclease in the replisome has proofreading, will degrade unpaired DNA
- geometry of strand is altered from a mismatch, leading to decrease in polymerase
activity
- primer:template junction is destabilized, creating several unpaired bases
- exonuclease has high affinity for ssDNA, will recognize and hydrolyze
unpaired/mismatched bases
3'-5' vs 5'-3' exonucleases - Answer✔️✔️-- 3' to 5' has proofreading and moves
backwards on the strand to removed mismatched bases
- 5' to 3' is not proofreading; repair for damaged DNA and removal of RNA
primers (Taq polymerase)
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