DNA Replication

What were the three hypothesis for DNA replication

conservative, dispersive, and semiconservative

Meselson and stahl in 1958 discovered that

DNA replication is semiconservative

DNA replication uses an old strand

as a template to direct synthesis of a new complementary strand

all replication starts at a

replication origin

replicon

unit that is replicated together

Theta replication

common in bacteria and other circular DNA molecules

DNA template is circular, their is no nucleotide strand breakage, and it produces two circular molecules

Rolling circle replication

the F factor and some viruses

circular, breaks the nucleotide strand, unidirectional, and ne circular molecule and one linear molecule that may circularize

Linear eukaryotic replication

for euk chromosomes which have multiple origins for replication along their length

linear template, no breakage of strand, bidirectional, and produces two linear molecules

replication can proceed in both direction from the origin

bidirectional replication

DNA polymerase 3 is responsible for the most

DNA synthesis (ELONGATES DNA)

DNA poly 3 proofreads with

3’-5’ exonuclease activity

DNA poly 1

was discovered first, functions 5-3’ to remove RNA primers

the phosphodiester bond formation

requires nucleoside triphosphates and catalyzation by DNA polymerase

DNA polymerase can only add

nucleotides 5’ to 3’

initiation process starts with the

initiator protein

the initiator protein (dnaA) binds to

origin of replication causing local unwinding and a short stretch of single-stranded DNA

Unwinding requires

Helicase, SSBs, and Gyrase

Helicase

attaches at replication fork and moves into the fork breaking the H-bonds as the replication fork moves along the DNA

SSB Single Stranded Binding proteins

coast single-stranded DNA to protect it, stabilize it, and prevent hairpins

Gyrase

is a topoisomerase that relieves supercoiling ahead of replicaiton fork

DNA polymerases must have an

3’ OH that they can add nucleotides to

RNA primers are made by

primase

primase is an

RNA polymerase

DNA pol 3 adds

nucleotides to the primer

primosome

helicase and primase

DNA pol 1

removes primer and fills the gap

a nick is a

missing sugar-phosphate bond

DNA ligase seals

nicks

Eukaryotic differences in replication

1. many origins of replication

2. linear chromosomes

3. have telomeres

replication licensing factor

attaches to each origin of replication early in the cell cycle

Licensing factors are only activated just after

mitosis and before

replication starts in cell cycle, so it will not be put back on an origin until

early in the next cell cycle.

telomerase is a

ribonucleoprotein that contains RNA and extends the 3’ end of the telomere