Unit 1 KA2 Structure & Replication of DNA

Question 1

What is the repeating unit in DNA called?

Answer 1

Nucleotides

Question 2

What composes each DNA nucleotide?

Answer 2

1. Phosphate
2. Deoxyribose Sugar
3. Base

Question 3

What are the 4 DNA bases and what they bond to?

Answer 3

Adenine bonds with Thyamine and Guamine bonds with Cytosine

Question 4

What shape is DNA?

Answer 4

Double helix

Question 5

How are the strands of DNA held together?

Answer 5

Through hydrogen bonds between the base pairs

Hydrogen bonds are quite weak, meaning the strands can be pulled apart easily

Question 6

What makes up the “backbone” of DNA?

Answer 6

Phosphate and deoxyribose sugar

Phosphate-sugar backbone

Question 7

Why is the sugar-phosphate backbone so strong?

Answer 7

Due to strong chemical bonds between the phosphate of one nucleotide and carbon 3 of another

Question 8

What does an antiparallel structure mean for DNA?

Answer 8

The strands run in opposite directions

One stand would go from carbon 5 to carbon 3, and the other would go from carbon 3 to carbon 5

Question 9

What shape do the DNA strands coil into?

Answer 9

A double helix

Question 9

Name the base pairs of DNA

Answer 9

Adenine - Thymine
Cytosine - Guanine

Question 10

Before cell division, what must happen to the DNA in the nucleus?

Answer 10

It must be replicated

Question 11

What enzyme replicates DNA?

Answer 11

DNA polymerase

Question 12

What are the stages in DNA replication?

Answer 12

1. Double helix unwinds
   2.Weak hydrogen bonds between base pairs break to form two template strands
   3.Template strands expose their bases at a Y-shaped replication fork
   4.One strand is a template for the leading strand and the other is a template for the lagging strand

Question 13

What is the DNA strand with the 3’ end exposed called?

Answer 13

Leading strand

Question 14

What is the DNA strand with the 5’ end exposed called?

Answer 14

Lagging strand

Question 15

What is the difference in replication between the leading and lagging strands?

Answer 15

Leading strand Replicates continuously
Lagging strand replicates in fragments (Discontinuously)

Question 16

Why is the DNA primer required for replication?

Answer 16

To create an existing chain for DNA polyermase to work on

Question 17

How are new nucleotides added to replicate the template strand?

Answer 17

They align with complimentary base pairs on the template strand and bind to the 3’ end of the primer

Question 18

What creates ssugar-phosphate bonds?

Answer 18

DNA polymerase

Question 19

Why does the lagging strand have to be replicated in fragments?

Answer 19

Because the only the 5’ end is exposed, and DNA polymerase can only add nucleotides to the 3’ end

Question 20

How are the fragments of the lagging strand joined together?

Answer 20

The enzyme ligase joins them together

Question 21

What are the 5 requirements for DNA replication?

Answer 21

1. DNA (to act as a template)
2. Primes (to create an existing chain for DNA polymerase to work on)
3. Free DNA nucleotides (A,T,G & C)
4. Enzymes (DNA polymerase and ligase)
5. ATP (energy)

Question 22

What does PCR stand for?

Answer 22

Polymerase chain reaction

Question 23

Why is PCR useful for genome sequencing?

Answer 23

Because it amplifies (replicates) DNA

Question 24

What are primers in PCR?

Answer 24

Short strands of nucleotides which are complimentary to specific target sequences at both ends of the region of DNA to be amplified.

Question 25

What temperture is DNA heated to in PCR stage 1?

Answer 25

To between 92-98°C

Question 26

What temperature is DNA cooled to in PCR stage 2?

Answer 26

To between 50-65°C

Question 27

What temperature is DNA heated to in PCR stage 3?

Answer 27

To between 70-80°C

Question 28

Why is DNA heated in PCR stage 1?

Answer 28

To break the hydrogen bonds between the strands, separating them

Question 29

Why is DNA cooled in PCR stage 2?

Answer 29

To allow primers to bind to target sequences

Question 30

Why is DNA heated in PCR stage 3?

Answer 30

To allow heat tolerant DNA polymerase can replicate the region of DNA

Question 31

What are the practical applications of PCR?

Answer 31

• Solving crimes
• Settling paternity disputes
• Diagnosing genetic disorders