10.2 DNA Replication (Eukaryotes)

Question 1

What is used instead of ori sequence in eukaryotes? Why

Answer 1

• DNA replication is initiated at multiple poisitions across a linear chromosome at ARS (autonomously replicating sequences); there are multiple on a linear chromosome.
• Each can initiate a replication bubble
• There are multiple because eukaryotic chromosomes are much longer than prokaryotic, so it helps ensure replication is done in sufficient time

Question 2

What is the goal of initiation in eukaryotes?

Answer 2

The same as prokaryotes, to open up the dsDNA to provide a template for DNA replication

Question 3

How does initiation occur in eukaryotes?

Answer 3

• ARS is recognized by a complex called the ORC (origin of replication complex), which then recruits other enzymes to create the pre-replication complex.
• preRC (prereplication complex) provides the licensing (permission) for replication to occur

Question 4

What unpacks chromatin in eukaryotes?

Answer 4

• Chromatin remodeling complexes and histone chaperones. NO gyrases involved in nuclear DNA replication (But are used to replicate organellar DNA)
• Unwinding the dsDNA is ore complicated because the DNA is wound around histone proteins to produce the nucleosomes. The nucleosomes must be disassembled and then immediately reassembled following DNA replication

Question 5

Elongation in eukaryotes

Answer 5

• Eukaryotes have more than 10 DNA polys, and different polys for leading and lagging strand synthesis

Question 6

Termination

What makes termination more complicated in eukaryotes?

Answer 6

• The end of the telomere has a region of ssDNA on the 3’ end (overhang)
• Issue because DNA replicated from the 3’ to 5’, so the only way to replicate the Dna is if there is a primer sequence to the right of the 3’ end.
• If there is no primer for DNA poly to work from, this sequence will not be replicated and w each round of replication, the chromosomes will get a little shorter

Question 7

Termination

What does telomerase do?

Answer 7

• Ribozyme (enzyme w protein and RNA components), special kind of DNA poly.
• RNA component is complementary to the telomeric 3’ overhang, allowing telomerase to bind to the end of the telomere.
• After binding, the Rna component still contains a ss domain. Telomerase uses its own RNA component as a template for DNA synthesis, adding more nucleotides to the overhand, extending the length of the chromosome