DNA Replication - Lecture 2

Question 1

How are nucleotides added onto the new strand of DNA during replication?

Answer 1

The 3’OH group of the sugar of the previous nucleotide on the new strand cleaves the 2 5’ end phosphate groups of the incoming dNTP and a phosphodiester bond forms between the two nucleotides

Question 2

Describe DNA replication in prokaryotes up until the addition of DNA polymerase.

Answer 2

• The binding of dnaA at the (OriC prok initiation site) AT rich region of the origin begins to unwind the strands
• DNA helicase is then added at each replication fork to continue unwinding
• Single stranded binding proteins are added to each strand to stabilize the single strand
• DNA gyrase works ahead of each replication fork and nicks the strand to relieve tension so DNA helicase can unwind
• DNA primase is then added to both replication forks and synthesizes an RNA primer
• The RNA primer provides the 3’ OH for DNA polymerase to add nucleotides
• On the leading strand, a primer is required only at the 5’ but at the lagging strand a primer is required at the 5’ end of each okazaki fragments

Question 3

What is the function of the four tandem 9-mer sequence in the OriC?

Answer 3

this sequence is recognized by dnaA so it can intiate replication (prokaryotes)

Question 4

What does DNA replication require?

Answer 4

Mg, DdDp, dNTPs, template strand, and RNA primers