Bio Ch 6

What is the role of helicase? Topoisomerases?

Helicase is the enzyme that unwinds the DNA strands. Topisomerases relieve the supercoils that result further down the DNA as helicase unwinds the strands

What does ligase do?

Ligase makes the final phosphodiester bond in the DNA after the primer is removed and replaced by DNA

Why is Telomerase needed? What does it do?

Telomerase is needed at the end of the lagging strand, after the primer is removed to fill in the end. It uses its RNA which can base pair with the end of the chromosome to add additional copies of the repeated end. Primer can then be put down and the end replicated

What is the leading strand in DNA replication? What is the lagging strand?

The leading strand is the strand being made in one continuous strand. The lagging strand is being made out of shorter Okazaki fragments

Why does DNA damage need to be repaired? How is it repaired?

DNA damage must be repaired to prevent changes in the DNA sequence. Damage (except double stranded breaks) is repaired by removal of the damaged section, filling in by DNA polymerase, and sealing the nick with DNA ligase. Double stranded breaks are repaired by non-homologous end joining or homologous recombination

What are Okazaki fragments? Why are they needed?

Okazaki fragments are the short strands that are made on the lagging strand of DNA replication. They are needed because DNA can only be made in the 5' to 3' direction and on one strand, this is opposite to the direction that the replication fork is traveling

What are primers made of? What enzyme makes them? Why are they necessary for DNA replication?

Primers are very short strands of RNA. They are made by the enzyme Primase which is an RNA polymerase. They are necessary to strand new DNA strands because DNA Polymerase needs a 3' OH group to add on to to make a DNA strand

What types of DNA damage need to be repaired?

Types of damage, depurination, deamination, thymidine dimers, mismatched bases, double stranded breaks