DNA Replication

phase 1 of protein synthesis

where does DNA replication occur

nucleus

what is the main goal of this process

to replicate genetic information before the splitting of the cytoplasm

stage 1

separating the DNA strand

what enzymes are used in stage 1

DNA helicase, DNA gyrase and single stranded binding proteins

DNA helicase

unwinds and splits double helix by snipping H bonds between nitrogenous base pairs

what is formed after DNA helicase splits nitrogenous bases apart

replication bubble

at the end of each replication bubble is

a replication fork (y-shaped region where DNA is actively opening)

DNA gyrase

relives tension caused during unwinding

single stranded binding proteins (SSB’s)

keep the 2 strands separated by binding to the exposed DNA sites to block H-bonding from re-occuring

stage 2

building the complementary strands

what enzymes are used in stage 2

primase, RNA primer and DNA polymerase III

primase

synthesizes RNA primer and lays it down on different sites of the single strands of DNA

RNA primer

acts as a marker that tells DNA polymerase III where to bind (must be activated and layed down by primase in order to work)

DNA polymerase III

binds to the RNA primer sites and lays down nucleotides along the daughter stands in the 5’— 3’ direction, using the template strand as a guide

what direction is the template strand read vs the direction in which DNA polymerase III builds

template strand reads 3’—5

DNA polymerase III builds in 5’ — 3’

template strand vs daughter strand

template strand runs antiparallel and reads in the 3’ — 5’

daughter strand is the new DNA being formed and built in the 5’—3’

types of daughter strands

leading and lagging

leading strand

DNA polymerase III continuously builds strand towards the replication fork

lagging strand

DNA polymerase III builds in okazaki fragments (short snippets of DNA) away from the replication fork

stage 3

proof reading

what enzymes are used in stage 3

DNA polymerase I and DNA ligase

DNA polymerase I

removes RNA primers and proof reads okazaki fragments

DNA ligase

joins the okazaki fragments together

quality control of new DNA strands

DNA polymerase I and III can also act as exonucleases

exonucleases/exonucleic enzymes

act as molecular scissors that cut and remove any incorrect nucleotide pairs and replaces it with the correct complementary base pair