DNA Structure & Function

Question 1

Name the DNA bases.

Answer 1

1. Adenine
2. Cytosine
3. Guanine
4. Thymine

Question 2

Which bases are purines and which are pyrimidines?

Answer 2

Purines: A + G, 9-membered rings

Pyrimidines: C + T, 6-membered rings

Question 3

How is DNA polarity denoted?

Answer 3

DNA has polarity denoted 5’ –> 3’

Question 4

How are deoxynucleotides linked?

Answer 4

Deoxynucleotides are linked by 3’ –> 5’ phosphodiester bond.

Question 5

What is the diameter of the helix?

Answer 5

The helix has a diameter of 20 Å.

Question 6

What distance separates two subsequent bases in the helix?

Answer 6

The bases are separated by 3.4 Å.

Question 7

How many bases (distance) does the helix structure repeat?

Answer 7

The helix repeats every ~10.5 bases (34 Å).

Question 8

What are the possible types of DNA helices?

Answer 8

B form (right handed)

• most prevalent form

A form (right handed)

• less prevalent

Z form (left handed)

• not common (transient)

Question 9

Who discovered DNA was the “transforming principle”?

Answer 9

Avery, MacLeod, McCarthy

Question 10

Describe the Avery, MacLeod, McCarthy experiment.

Answer 10

Experiment:

Question 11

What factors influence DNA denaturation (melting)?

Answer 11

higher GC content –> higher Tm

higher [salt] –> higher Tm

longer DNA length –> higher Tm

Question 12

How do circular chromosomes resolve topological constraints?

Answer 12

They require topoisomerase activity to resolve topological constraints.