Chapter 4.2 The Double Helix

Question 1

What are the 4 nucleotides bases found in DNA

Answer 1

• Adenine (A)
• Guanine (G)
• Cytosine (C)
• Thymine (T)

Question 2

What is the backbone of DNA made of?

Answer 2

Phosphates and deoxyribose

DNA stands for Deoxyribonucleic Acid

Question 3

Phosphates connect from what carbon to what carbon?

Answer 3

From 3’ to 5’ of the adjacent sugar

Question 4

The two strands of DNA are what kind of parallel?

Answer 4

Antiparallel

Question 5

The two strands of DNA have ___________ base sequences

Answer 5

Complementary

Question 6

What shape do the two strands form?

Answer 6

A Double Helix

Question 7

Some information about DNA that you only will need to know if you are getting a PhD in microbiology

Answer 7

• Size of DNA molecule is expressed in base pairs
• 1,000 base pairs = 1 kilobase pair = 1 kbp
• 1 million base pairs = 1 megabase pair = 1Mbp
• E. coli genome = 4.64 Mbp
• Each base pair takes up 0.34 nm of length along
the helix
• 10 base pairs make up 1 turn of the helix

Question 8

What is it called when DNA is further twisted to save space?

Answer 8

Supercoiled DNA

Question 9

What are the two different kinds of supercoiling?

Answer 9

• Negative supercoiling: double helix is underwound

* Positive supercoiling: double helix is overwound

Question 10

When DNA has a corresponding amount of turns predicted by the number of base pairs it is known as what?

Answer 10

Relaxed DNA

Question 11

What enzyme introduces supercoils into DNA

Answer 11

DNA gyrase