Lecture 4 DNA Replication I

Question 1

Define buoyant density

Answer 1

this is the density possessed by a molecule or particle when suspended in aqueous salt or sugar solution

Question 2

Define DNA topoisomerase

Answer 2

This is an enzyme that cuts the DNA and eases the tortional strain, and relaxes the DNA during replication by making nicks

Question 3

Define plectonemic

Answer 3

this is a helix whose strands cannot be separated without unwinding first

Question 4

What is a type I DNA topoisomerase

Answer 4

An enzyme that makes a single stranded nick in double stranded DNA.

Question 5

What is a type II DNA Topoisomerase

Answer 5

an enzyme that makes a double stranded nick in double stranded DNA, relieving the stress, and allowing the DNA to unwind.

Question 6

Explain how semi-conservative replication works

Answer 6

This is where the daughter DNA molecules are comprised of one of each of the orignial strand and the other strand is newly synthesised polynucleotide

Question 7

Why did scientists originally believe that the semi conservative mode of repliation was not possible.

Answer 7

• DNA is plectonemic (the strands cannot separate without unwinding)
• A lot of DNA is circular, thus the problem of how does a circle unwind arose.
• This was before topoisomerases were discovered.