Eukaryotic and Prokaryotic DNA Replication: Key Similarities and Differences

What are the overall similarities between DNA replication in eukaryotes and prokaryotes?

Both use helicases to unwind DNA, SSB proteins to hold ssDNA apart, RNA primers for polymerase, clamp proteins for processivity, and various DNA polymerases for synthesis.

Where does DNA replication occur in eukaryotes?

In the nucleus.

What are some differences between eukaryotic and prokaryotic DNA replication?

Eukaryotes have more genetic material, multiple linear chromosomes, additional packaging like nucleosomes, and multiple origins of replication per chromosome.

What is the role of autonomously replicating sequences (ARS) in DNA replication?

They are sections of DNA where origins of replication arise, separated by approximately 30 kb.

What is the function of the origin recognition complex (ORC) during DNA replication initiation?

It binds to the A region of the origin of replication.

What proteins accumulate in the nucleus during the G1 phase to assist in DNA replication initiation?

Licensing factors such as cdc6 and cdt1.

What is the function of helicase in DNA replication?

It unwinds the DNA duplex and moves 3' to 5' on ssDNA via ATP hydrolysis.

What happens during the activation of helicases in the S phase?

The pre-replication complex is activated by additional proteins and phosphorylation.

What are the five main eukaryotic DNA polymerases?

Alpha, beta, gamma, delta, and epsilon.

What is the role of polymerase alpha in DNA replication?

It makes primers and has its own primase activity but lacks proofreading capability.

What is the function of the clamp loading complex (RFC) in DNA replication?

It loads the sliding clamp protein PCNA onto a primer, displacing polymerase alpha.

What is the significance of PCNA in DNA replication?

It is a homotrimer that binds primers and holds polymerases onto ssDNA.

How are Okazaki fragments affected during DNA replication in eukaryotes?

Nucleosomes must be removed and replaced, which shortens the Okazaki fragments.

What is the role of flap endonuclease-1 (FEN1) in primer removal?

It recognizes 5' RNA flaps produced by polymerase delta and cleaves off approximately 15 nt.

What is the Hayflick limit in relation to telomeres?

It is the point at which gene loss can occur after approximately 40 cell divisions due to telomere shortening.

What is telomerase and its function?

A ribonucleoprotein that synthesizes more telomeric DNA, allowing cells to overcome the Hayflick limit.

What is unique about mitochondrial DNA replication compared to nuclear DNA replication?

It involves unidirectional replication with two origins and uses mitochondrial-specific proteins.

What are the two origins of replication in mitochondrial DNA?

OH (heavy) and OL (light).

What is the function of TWINKLE helicase in mitochondrial DNA replication?

It unwinds the circular mtDNA in a 5' to 3' direction.

What is the difference in the speed of DNA polymerases between eukaryotes and prokaryotes?

Eukaryotic DNA polymerases are slower, synthesizing at about 50 nt/s compared to 1000 nt/s in prokaryotes.

What is the role of polymerase delta during DNA replication?

It synthesizes the lagging strand and associates with PCNA for proofreading.

What happens to replication forks from one origin during DNA replication?

They can pass through another origin, a process known as passive replication.

What occurs at the end of DNA replication in eukaryotes?

Replication forks migrate to the end of chromosomes and detach, with decatenation occurring during elongation.