Flashcards in EXAM2_L14_DNA_Replication Deck (21)
1. duplicates entire genome
2. once per cell cycle
4. bi-directional replication until rep forks collide or end of chromosome reached
5. semi-discontinuous (lagging strand)
Mechanism of replication 1,2,3.
1. Initiation (proteins bind to DNA, open helix, prepare DNA for base pairing)
2. Elongation (proteins connect nucleotides into continuous new DNA strand)
3. Termination (proteins release replication complex)
Origins of replication- structure, proteins used, function.
Multiple origins in DNA w/ TATA rich sequences.
Origin binding proteins separate DNA forming a replication bubble where other proteins recruited to replicate DNA
DNA Helicase- function
unwinds and extends replication fork in 5'to3' direction respective of leading strand.
- Req ATP
binds ssDNA to prevent strands from reattaching after helicase unwinds the DNA.
- prevents DNA degradation
two ways of orienting 5' to 3'
Growth of new daughter strand is always 5' to 3'
Growth always occurs toward the 5' end of the Parent strand
what are 4 components req for replication?
2. ssDNA template
3. a free 3' OH group
4. RNA primer (b/c dna pol cant make strands denovo)
7 proteins of replicaiton
4. DNA Pol
5. RNase H
6. DNA ligase
What drives replication?
ATP and energy from phosphates on nucleotides.
-Makes it almost irreversible reaction
Three rules for DNA Polymerase. Types of DNApol?
1. copy ssDNA
2. add bases ONLY to existing chains (base pairing)
3. ONLY extend from 5' to 3' direction
-alpha, epsilon, gamma (major replicative DNApol)
How does replication get started?
Primase makes RNA primer
-primer makes short dsRNA base-paired to DNA template with 3'-OH
-RNA portion removed/replaced with DNA later
Inhibition of DNA synthesis (types,examples,mech)
NRTI- nucleoside reverse transcriptase inhibitor (anti-HIV)
Have no 3' carbon OH so no elongation occurs
DNA Pol alpha
proofreads/ manages replication
-recognizes RNA-DNA duplexes and removes the primer, leaving the DNA part intact
1. between okazaki fragments
2. between colliding replication forks
important for DNA to identify new daughter strand when repairing
How are okazaki fragments numbered?
first fragment is #1 and counts up to the newest fragment.
Supercoil unwinding ahead of helicase.
Type 1 cuts ONE strand
Type 2 cuts BOTH strands
What are two topoisomerase inhibitors for type 1 and 2? Why used? 2 modes?
Camptothecin Topoisomerase I inhibitor
Doxorubicin Topoisomerase II inhibitor
-cancer Chemotherapeutic agents
1. prevent unwinding
2. prevent re-sealing
both cause cell death
Telomeres structure funciton
end of linear chromosome
-ds and ss DNA
-composed of thousands of repetitive sequence of non-coding DNA
-Protects DNA from damage
End-replication problem. How solved?
-successive rounds of DNA replication on lagging strand will produce daughter strands that are progressively shorter
When final RNA primer (lagging strand) removed, there is no way to replace it with DNA