Unit 1: human cells- Structure and replication of DNA

Question 1

What does DNA consist of?

Answer 1

Units called nucleotides.

Question 2

What are nucleotides made of?

Answer 2

Phosphate, deoxyribose sugar and a base.

Question 3

What forms the genetic code?

Answer 3

The base sequence.

Question 4

What holds each strand of DNA together?

Answer 4

Each individual strand of DNA is held together by a strong chemical bond between the phosphate of one nucleotide and the carbon 3 of the sugar, on another nucleotide.

Question 5

What holds the bases in adjacent strands together and what does this cause?

Answer 5

Weak hydrogen bonds hold the bases together and makes it coil into a double helix structure.

Question 6

What does the 3’ end of a DNA strand have?

Answer 6

A deoxyribose sugar.

Question 7

What does the 5’ end of a DNA strand have?

Answer 7

A phosphate.

Question 8

What end can nucleotides only be added to?

Answer 8

The 3’ end.

Question 9

What are the 4 different bases?

Answer 9

Adenine, Guanine, Cytosine and Thymine.

Question 10

What do the 2 DNA strands have running in different directions?

Answer 10

The phosphate backbone.

Question 11

What is the double helix described as having?

Answer 11

The double helix is described as having two anti-parallel chains of nucleotides as one side goes from the 5’ to 3’ and the opposite side goes from 3’ to 5’.

Question 12

What is DNA polymerase and what is it’s function?

Answer 12

DNA polymerase is an enzyme that controls the formation of the sugar phosphate bonding of the nucleotides into the DNA stand. This enzyme can also add nucleotides to the 3’ end of a growing DNA chain.

Question 13

What is a primer?

Answer 13

A short sequence of nucleotides at the 3’ end.

Question 14

What strand has to be replicated in fragments?

Answer 14

The 5’ end.

Question 15

What is the 5’ end also called and why is this?

Answer 15

The lagging strand as it has to be replicated in fragments and is slower than the 3’ end.

Question 16

What is the 3’ end also called?

Answer 16

The leading strand.

Question 17

What is ligase and what does it do?

Answer 17

Ligase is an enzyme that joins all the DNA fragments together once they are all in place.

Question 18

For DNA replication to occur, what must the nucleus contain?

Answer 18

Primers, DNA (template), enzymes ( DNA polymerase and ligase), ATP and nucleotides.

Question 19

Where does DNA replication occur?

Answer 19

In the nucleus.

Question 20

Why is DNA replication important?

Answer 20

DNA replication is important so that when cells divide they have the correct genetic information they need to function properly and so that no information is lost.

Question 21

Why is a primer needed in DNA replication?

Answer 21

A primer is needed in DNA replication because DNA polymerase can only add nucleotides to the 3’ end.

Question 22

What is the function of PCR/ what does PCR do?

Answer 22

PCR AMPLIFIES DNA (it creates many copies of a piece of DNA in vitro outside the body).

Question 23

What are the steps involved in PCR?

Answer 23

1) DNA is heated to break the hydrogen bonds and separate the strands.
2) it is then cooled to allow primers to bind to the target sequence of DNA.
3) Heat tolerant DNA polymerase then adds nucleotides to the primers ( at the 3’ end of the original DNA strands).

Question 24

What are practical uses of PCR?

Answer 24

• solve crimes ( if not enough DNA is found to work on, it can be amplified so the forensics people have more to work with i.e. DNA profiling)
• diagnosing genetic disorder
• paternity tests

Question 25

What is the role of ligase?

Answer 25

Joins fragments of DNA at the 5’ end of the lagging strand.