BIO 221: Prokaryotic and Eukaryotic Replication

Structure of prokaryotic chromosomes

a single circular DNA molecule located in the cytoplasm, has histone-like proteins, origin of replication, and terminator

What proteins organize/package prokaryotic chromsomes?

histones (in the middle)

When does prokaryotic DNA replication begin?

origin of replication

When does prokaryotic replication terminate?

When the two forks heading in opposite directions fuse together (terminus region)

histone-like proteins

help organize and package dsDNA within nucleoid

Helicase in prokaryotic replication

binds to the origin of replication w/ help from ssDNA binding proteins (separates DNA) by breaking hydrogen bonds

Primase in prokaryotic replication

primase synthesizes RNA primers that are complementary to template strands

primasome

complex formed by primase and helicase that is essential for initiating replication

Topoisomerase in prokaryotic replication

prevents supercoiling on the replication forks by breaking and rejoining phosphodiester bonds

DNA polymerase III (continuous) in prokaryotic replication

synthesizes the leading strand in 5' to 3' direction

DNA polymerase III (discontinous) in prokaryotic replication

primers fill gaps on the opposing side of the leading merging with Okazaki fragments (5' to 3')

Okazaki fragments

Short DNA fragments synthesized in lagging strand

What do lagging strands leave behind?

"nicks" (unformed phosphodiester bonds) which are left behind after Okazaki and primer merge

DNA ligase

seals nicks left behind by lagging strand with phosphodiester bonds

DNA replication fidelity

DNA polymerase III works very fast and efficiently w/ little to no errors due to proof-reading (10^-11)

Regulation of prokaryotic DNA replication

dnaA protein which starts low but increases with cell volume to send signal when cell is ready to divide

Function of dnaA protein

recruits helicase to the origin of replication

Eukaryotic vs Prokaryotic replication

Eukaryotes have multiple origins and five primary polymerases

Structure of eukaryotic chomosomes

multiple orgins of replication merge together as they replicate DNA

Five polymerases of eukaryotes

DNA polα, DNA pol δ, DNA polε, DNA polγ, DNA polβ

DNA polymerase α (alpha)

primase (synthesizes RNA then switches to DNA)

DNA polymerase δ (delta)

lagging strand synthesis

DNA polymerase ε (epsilon)

leading strand synthesis

DNA polymerase γ (gamma)

mitochondrial DNA synthesis (more complex than normal DNA)

DNA polymerase β (beta)

DNA repair

Regulation of eukaryotic DNA replication

Cell cycle phases

Cell cycle phases

Interphase, M phase, Cytokinesis

Interphase

G1, S phase, G2

G1

cell growth

S phase

DNA synthesis and replication occurs

G2

Cell prepares to divide

M phase

mitosis/meiosis

Mitosis vs Meiosis

Mitosis is cell division of two identical daughter cells while meiosis is sexual reproduction using gametes

Cytokinesis

cytoplasm divides resulting in two separate daughter cells

Initiating of eukaryotic DNA replication

ORC complex attaches to origin attracting Cdc6/Cdt1 which then binds MCM leading replication

Ending of eukaryotic DNA replication

replication begins detaching Cdc6/Cdt1 from the ORC complex causing MCM to leave

Ending of cell growth/mitosis

G2 phase nuclei contain geminin which prevents MCM from binding; geminin degrades once mitosis is complete

What happens if licensing doesn't happen correctly?

can never replicate DNA, cell division isn’t possible, Meier Gorlin Syndrome

Meier Gorlin Syndrome

mutations in genes encoding ORC proteins, Cdt1, Cdc6

Symptoms of Meier Gorlin Syndrome

short stature, absence of patella, small ears (cell division is not happening at a normal rate)