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50 Cards in this Set
- Front
- Back
What are the characteristics of prokaryote replication?
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1. Prokaryotes lack nucleus, 2. circular chromosome, 3. Origin of replication, 4. strands separated at origin -> synthesis begins in both directions -> creates a replication bubble -> proceeds till two separate circles are made
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Function of topoisomerase?
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Relieves supercoiling
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Function of helicase?
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Unwinds helix to separate pairs
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Function of single stranded binding protein
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Maintains strands to be single
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What is the function of DNA polymerase?
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Synthesizes new strand; works in 5'-> 3' direction(adds dNTP to 3' OH group of chain); PYROPHOSPHATE degraded to keep equilibrium conditions favoring synthesis of DNA
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What strand has continuous synthesis?
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Leading strand; replication fork opens up ahead of polymerase in RIGHT direction
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What strand is synthesized in opposite directions(away from fork)?
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Lagging strand; replication fork uncovers DNA behind polymerase-> thus has to start many times
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What are the error prevention mechanisms?
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DNA polymerase can correct errors -> contains 3' -> 5' exonuclease activity (aka digest DNA from 3' end); activated by mis-match Base pairing -> cuts off incorrect base -> moves back along strand -> inserts new nucleotide
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What enzyme makes RNA primers needed for replication?
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Primase
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What strand requires and RNA primer in multiple locations?
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Lagging strand
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Which strand undergoes discontinuous synthesis?
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Okazaki fragments (1k-2k bp) requires RNA primers to start the polymerization; RNA primers need to b converted back to DNA -> RNAase H digests RNA hybridized DNA -> DNA polymerase enters -> lays down DNA -> DNA ligase seals the nick between the 2 new DNA fragments made
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Function of DNA ligase?
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Closes nicks in DNA backbone at 3' end
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During the eukaryotic cell cycle: what phase duplicates chromosomes?
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S phase only
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How does a eukaryotic cell ↑ the speed of replication?
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1. multiple origins of replication thus forming multiple bubbles, 2. forks are bi-directional
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Function: Polymerase I
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• Replication, Repair, Primer excision
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Function: Polymerase II
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• DNA Repair
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Function: Polymerase III
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• Major replication polymerase, 3’-5’ exonuclease for proofreading activity
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Function: Polymerase a
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• Associated with primase
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Function: Polymerase g
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• Mitochondrial DNA synthesis
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Function: Polymerase b
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• DNA repair, primer excision
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Function: Polymerase d
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• Replication, 3’-5’ exonuclease for proofreading
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Function: Polymerase e
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• DNA repair
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Topoisomerase vs DNA gyrase
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Topoisomerase = eukaryote enzyme that relieves supercoiling of DNA, DNA gyrase = prokaryotic enzyme that relieves supercoiling
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What drug targets NDA gyrase?
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Quinolone anti-biotics
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What are the 2 types of eukaryotic topoisomerase?
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Type 1 = 1 cuts one strand, Type 2 = 2 cuts both strands
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Function of helicase
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Opens double helix -> separates strands by breaking hydrogen bonding between strands
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What happens to linear chromosomes lagging strand?
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It contains a 3' overhand -> single stranded DNA can be degraded and lost; How to prevent this? Use telomerase
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Function of telomerase?
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Lengthens telomeres (repetitive DNA sequences at the end of a chromosome) contains RNA complementary sequence -> uses reverse transcriptase to elongate; important in senescence (in ability for cell to continue to divide)
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What enzyme is used in cancer cells to enable them to keep dividing?
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telomerase
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What is the procedure for DNA repair?
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1. Identify damage, 2. remove damage(endo/exonuclease), 3. repair polymerase fills in gap, 4. DNA ligase seals nick
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What is the chemical in tobacco that attacks cellular DNA?
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Benz[a]pyrene -> oxidized in body -> reacts w/guanine -> distorts helix
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How does UV damage DNA?
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UV creates thymine dimer (T-T)(two pyrimidines covalently linked) -> distorts double helix
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What does cytosine deaminate into?
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Cytosine -> uracil
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What does 5-methylcytosine deaminate into?
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5-methylcytosine (aka cytosine)-> thymine
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Function of nucleotide excision repair?
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Cuts out damaged nucleotides
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Function of base excision repair?
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Removes abnormal base, leaves backbone intact
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Function of mismatch repair?
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Cuts out incorrect base, depends on methylation to identify strands
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Function of transcription coupled repair?
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Repairs transcribed genes preferentially
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Function of glycosylase?
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Removes only one base
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Function of endonuclease
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Removes damaged nucleotides(groups of DNA) + cuts backbone w/missing bases
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Function of exonucleases
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Removes adjacent bases -> creates a gap
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Which DNA strand is the original strand? Newly synthesized strand?
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Original strand has methylated bases (Ch3); newly synthesized strand = no methylation
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Pt w/ UV exposure -> skin lesion -> NUCLEOTIDE EXCISION REPAIR DEFECT -> accumulation of DNA defect in skin -> tumors
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Xeroderma pigmentosum
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Pt w/ DEFECT IN MISMATCH REPAIR GENES -> accumulation of mutations over time -> cancer
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Hereditary non-polyposis colorectal cancer
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What are the mechanisms used for DNA rearrangements?
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1. Recombination, 2. translocation, 3. transposable element, 4. retroviral insertion
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What is the holiday structure?
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The combination of parental chromosomes during meiosis
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Define: translocation
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Genetic material exchanged between non-homologous chromosomes -> happens in cancer
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Define: transposable elements
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Jumping genes - mobile genetic elements -> cuts out of old position -> finds new site
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Define: retroviral insertion
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RNA Viruses -> reverse transcriptase -> cDNA copy of RNA genome ->RNA degraded-> makes ds cDNA -> DNA is incorporated into cell DNA
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What are the drugs that are chain terminators?
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1. AZT (zidovudine, retrovir), 2. dideoxycytidine (zalcitabine, DDC); MOA = incorporated into growing chain and since DNA polymerase lacks proofreading it cant remove the base and it stops synthesis of DNA)
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