DNA Replication And Repair Flashcards
Covalent structure of DNA
. Double stranded polymer of deoxyribonucleotides joined by 3’-5 phosphodiester bonds
Hydrogen bonding between base pairs in DNA
. 3 hydrogen bonds with ____
. 2 H bonds w/ ______
. Stabilizes double helix in non-polar interior
Is phsophodiester connection btw deoxynucleotides directional or not?
. Directional
. Connects 5’ phosphate of 1 nucleotide w/ 3’ hydroxyl group of next nucleotide
DNA replication occurs in what phase of cell cycle?
S phase
Substrates for DNA replication
??
Product of DNA replication
2 identical strands???
DNA polymerase
. Select nucleotide that is added to 3-OH end of chain
. Catalyzes formation of phosphodiester bond
. Substrates are dATP, dCTP, dGTP, and dTTP and single stranded template DNA
T/F there is one place for replication to begin
F, there are multiple sites that start at different times
. When it nears completion the bubbles of newly replicated DNA meet and fuse forming 2 new molecules
DNA chain elongation
. DNA polymerase adds deoxyribonucleotides to 3’ end of growing chain
. Dictated by base sequence of template (coding) strand
New DNA strand is synthesized in what direction?
5’ to 3’ because it is antiparallel
Leading strand DNA replication
. 5’-3’
. In same direction as replication fork movement
.
Landing strand DNA replication
. 5’ to 3’
. Synthesis in direction opposite of fork movement
. Short (100-200 nucleotides) fragments (Okazaki fragments) made
. Lipase joins fragments together
DNA helicase
. Unwinds short segment of parental duplex DNA by catalyzing ATP dependent strand separation
. Forms replication fork
DNA primase
. Initiates synthesis of RNA molecule that primes DNA synthesis on leading and lagging strand
. First few nucleotides are ribonucleotides and then subsequent ones are ribo or deoxyribonucleotides
Singles stranded DNA binding proteins during replication
. Bind to single stranded DNA
. Prevent premature annealing of single stranded DNA to double stranded
Proof reading in DNA replication
. DNA polymerase w/ 3’-5’ exonuclease activity
. Remove nucleotides that aren’t part of double helix and are mismatched
. Do not has 5’-3’ exonuclease activity
DNA ligase
. Seals nick in DNA after DNA polymerase fills gaps left by RNA primers
Topoisomerases
. Facilitates unwinding of double helix super twisting to achieve negative supercoils for transcription
. As replication fork moves, daughter molecules rotate around each other and become overcoiled
. Relieve torsional stress by inducing reversible single stranded breaks in DNA at phosphodiester bond
Topoisomerase I
. Catalyzes break in only 1 strand of DNA
. Allows unwinding of broken strand
. Rejoin broken ends by catalyzing formation of new phosphodiester bonds
Topoisomerase II
. Catalyzes break in both strands of DNA
. Both strands unwind
. Catalyzes formation of new phosphodiester bonds
Classes of DNA synthesis inhibitors
. Prevent/reduce purine/pyrimidine synthesis (_____)
. Drugs affect template/priming ability of growing strand (intercalating agent doxorubicin for cancer)
. Topoisomerase inhibitors
DNA gyrase
. Bacterial type II topoisomerase
. Introduces neg. supercoils into DNA molecules via ATP dependent reaction ahead of replication fork
quinolone antibacterials
. 1st and 2nd generation: Norfloxacin and ciprofloxacin
. 3rd generation: levoflaxacin and moxifloxacin
. DNA gyrase inhibitor via inhibiting strand cutting reaction
Camptothecins
. Anti cancer agents
. Inhibit topoisomerase I
Doxorubicin, etoposide, and teniposide
. Inhibit human topoisomerase II
. Anti-cancer drugs
. Enhances rate at which topoisomerase II cleaves or reduces rate at which the breaks are resealed