BIOL 102 Final: Day 13

Extra Credit

A relaxed, circular, double-stranded DNA of 4400 base pairs is in a solution where the conditions favor a DNA structure of 10 base pairs per turn.

What are the values for Lk, Tw, and Wr (3 points)?

During replication, 400 base pairs of this DNA are unwound while the rest of the DNA still favors 10 base pairs per turn. What are the new values of Lk, Tw, and Wr (3 points)?

PLEASE ANSWER FULLY!

How are Lk (linking number), Tw (twist), and Wr (writhe) inter-related? How many based pairs per turn in relaxed DNA, positively and negatively supercoiled DNA? What is the biological significance of supercoiling? When does it occur? Is it a good thing or a bad thing? What enzymes are involved in changing DNA topology, and what is their mode of action?

What is the relative gene order, and the map distance between these genes, based on thefollowing results from this three point mapping cross:

a B d 404

A b D 395

A B d 210

a b D 195

a B D 15

A b d 19

a b d 154

A B D 139