Replication Flashcards
(45 cards)
Complementary DNA pairs
A+T and C+G
Pyrimadine
C+T
Purine
G+A
How many bp in a turn of the DNA double helix?
10 bp/turn
Length of a helical turn?
3.4 nm/turn
Distance between bases?
0.34 nm
DNA replication is?
Semi-conservative:
After one round of DNA replication, each DNA contains one parental and one newly-synthesized strand.
What is DNA synthesis not?
Conservative: Formation of a completely new molecule; after one round one parental molecule and one new molecule.
Dispersive: Parental molecule is completely disrupted and reassembled to make a new strand; half of the ds-DNA is the parental and the other half of the helix is new.
Why is DNA replication important?
Ensures an exact copy.
If DNA failed to copy, meiosis and mitosis would not occur, and life would not exist.
What are the three modes of DNA replication?
Theta replication, Rolling circle replication, Linear chromosome replication.
What is theta replication?
(Unwind, replication bubble, replication fork, replication)
- Occurs in most circular DNA
- Replication is bidirectional
- Two circular DNA molecules are produced
What is rolling circle replication?
(Break in nucleotide strand, replication of inner strand, cleavage releases a ss-linear DNA and ds-DNA)
- Occurs in the F factor of some viruses
- Replication is unidirectional
- Produces multiple circular DNA molecules
What is linear chromosome replication?
(Unwinding, replication bubble, DNA synthesis on both strands at each end of the bubble as replication forks form, forks meet and segments fuse)
- In eukaryotes
- Replication is bidirectional
- Produces two linear DNA molecules
What is required for DNA replication?
- Requires magnesium
- DNA polymerase
- dNTPs
- A template strand
- RNA primer
What are the features of DNA replication?
- Synthesized 5’ to 3’
- New strand is complementary and antiparallel to template
- Held together by hydrogen bonds
DNA chains are susceptible to nuclease cleavage…
… can cleave a phosphate group attached to 5’ or 3’ carbon
(gamma, beta, alpha phosphate attached to nitrogenous base)
What is a nucleotide?
Phosphate group + a sugar + a nitrogenous base
Where is DNA synthesis continuous?
On the leading strand
- By polymerase III
Where is DNA synthesis discontinuous?
On the lagging strand creating Okazaki fragments (short fragments of DNA produced by discontinuous synthesis).
- By polymerase III and polymerase I fills in the gaps
Where does DNA replication begin?
From an “origin”
What does prokaryotic DNA replication consist of?
- oriC orgin site
- four dnaA binding sites
- an AT rich region that undergoes strand seperatio n
What is helicase?
Unwinds DNA in the 5’ to 3’ direction
- Breaks hydrogen bonds and moves the replication fork
- Binds to the lagging-strand template at each replication fork
What are single-strand-binding proteins?
Immediately binds to the single-stranded DNA after helicase unwinds it.
- Keeps DNA linear so it does not fold back on itself
- Allows DNA to be easily replicable
What is DNA gyrase?
Topoisomerase II:
- Encircles DNA and removes torsional stress caused by the helicase unwinding which causes positive supercoils that can stop replicaiton (no more unwinding)
- Nicks DNA to release supercoils
- Relieves strain ahead of the replication fork
