AP BIo Unit 6 Topic 2: Replication

origins of replication

-where dna replication begins -various proteins attach to the origin of replication and open the dna to form a replication fork

replication fork

A Y-shaped region on a replicating DNA molecule where new strands are growing.

primase

An enzyme that joins RNA nucleotides to make the primer using the parental DNA strand as a template.

helicase

An enzyme that untwists the double helix of DNA at the replication forks.

nuclease

DNA cutting enzyme

topoisomerase

Enzyme that functions in DNA replication, helping to relieve strain in the double helix ahead of the replication fork.

DNAP I

Removes RNA primer with its 5'-3' exonuclease activity and fills in ssDNA gaps with its 5'-3' polymerase activity

Okazaki fragments

Small fragments of DNA produced on the lagging strand during DNA replication, joined later by DNA ligase to form a complete strand.

mismatch repair

The cellular process that uses specific enzymes to remove and replace incorrectly paired nucleotides.

lagging strand

The strand that is synthesized in fragments using individual sections called Okazaki fragments

DNAP III

attaches to each primer on the parallel strand and moves in the 3' to 5' direction

models of DNA replication

conservative: -the parental strands direct synthesis of an entirely new double stranded molecule semiconservative: -the two parental strands each make a copy of itself dispersive: -the parental strand would contain a random mix of new DNA

if an error occurs in dna replication how is it fixed

dna polymerase adds nucleotides to the new dna strand to proofread the bases added.

dna ligase

joins the okazaki fragments forming a continuous dna strand

telomeres

repeating units of short nucleotides sequences that do not code for genes

in which stage of the cell cycle does DNA replicate

s phase

primers

short segments of DNA that guide DNA polymerase to the section of DNA to copy

leading strand

synthesized continuously

describe step by step how dna is replicated

the dna will open up at the origins of replication then form a replication fork. the helicase prevents the dna from unwinding and the topoisomerase prevents strain. to keep the dna from rebonding with itself ssbp are bound to it. then primase adds short segment of RNA (primers). DNAP III attaches itself to a primer and in to the 3'to5' direction and adds nucelotides to the 5'to3'. the leading and lagging strands are syntehsized and DNAP I attaches to a primer and replaces RNA nucleotides to DNA nucleotides

telomerase

the enzyme telomerase adds telomeres to DNA

decribe the meselson and stahl experiment that supported the semi conservative model DNA replication

the experiment consisted of three stages. first bacteria were cultured with a heavy isotope called N15. Then the bacteria were transferred to the medium with N14, a light isotope, and was permitted to replicate. The DNA was then centrifuged and analyzed after each replication. When the bacteria were analyzed it produced a pattern, G0 only produced bacteria with N15 DNA. G1 also only produced N15. The G2 bacteria produced were 100% intermediate, further supporting the semiconservative model.