1.2 DNA & its replication

Question 1

What are the repeating units which each strand of DNA is made of?

Answer 1

nucleotides

Question 2

How many different components are each nucleotide made of ?

Answer 2

3

Question 3

What does each nucleotide include?(3)

Answer 3

a phosphate group
a deoxyribose sugar
a base

Question 4

What is the only thing that makes one nucleotide different from the other?

Answer 4

the base

Question 5

What are the 4 different types of base that exist in DNA?

Answer 5

Adenine
Thymine
Guanine
Cytosine

Question 6

What name is given to DNA because it consists of 2 strands wound together in to a spiral ?

Answer 6

double helix

Question 7

What are the nucleotides which makeup up each strand joined by?

Answer 7

a strong chemical bond between the deoxyribose sugar of one group and the phosphate of the next forming a sugar-phosphate backbone.

Question 8

What are the two strands of the DNA held together by?

Answer 8

weak hydrogen bonds between bases on each strand

Question 9

What are the base pairs?

Answer 9

adenine-thymine

guanine-cytosine

Question 10

What do both strands of DNA in the double helix have?

Answer 10

a 3’ and a 5’ end

Question 11

What do both strands of DNA in the double helix run in?

Answer 11

opposing directions to each other

Question 12

What is DNA described as because it runs in opposing directions to each other?

Answer 12

anti-parallel

Question 13

How can the 5’ end of a strand be identified ?

Answer 13

it terminates in a phosphate group

Question 14

How can the 3’ end of a strand be identified?

Answer 14

it terminates in a deoxyribose sugar group

Question 15

How many hydrogen bonds does the base pair A-T have?

Answer 15

2

Question 16

How many hydrogen bonds does the base pair

G-C have?

Answer 16

3

Question 17

The vast amount of DNA present must be packaged to allow it to fit into the nucleus of cells. How is this achieved?

Answer 17

DNA is tightly coiled around protein molecules called histones and arranged to form chromosomes.

Question 18

What are nucleosomes?

Answer 18

DNA + histones

Question 19

What are nucleotides?

Answer 19

subunits which make up each strand of DNA

Question 20

What is meant by double helix?

Answer 20

2 strands held together by hydrogen bounds wound into a spiral conformation.

Question 21

What are chromosomes?

Answer 21

structures contained within the nucleus of cells consisting of tightly wound DNA and proteins.

Question 22

What is a histone?

Answer 22

protein around which DNA is coiled and packaged

Question 23

What must be made before cells divide and what is this process called?

Answer 23

An exact copy of DNA called DNA replication

Question 24

What does the process of DNA replication produce?

Answer 24

2 identical DNA molecules from 1 parent molecule

Question 25

What is stage 1 of DNA replication ?

Answer 25

For DNA replication to take place, the double helix of DNA must unwind/uncoil and unzip, with hydrogen bonds between complimentary bases breaking to present two template strands

Question 26

What is stage 2 of DNA replication?

Answer 26

A primer, a short strand of nucleic acid, binds to the complementary target sequence at the start of the sequence of bases to be replicated.

Question 27

What is stage 3 of DNA replication?

Answer 27

This allows the enzyme DNA polymerase to synthesise a new strand of DNA by adding the bases complimentary to the template strand

Question 28

What is stage 4 of DNA replication ?

Answer 28

DNA polymerase can only add nucleotides to the 3' end of the growing strand due to the configuration of nucleotides. DNA polymerase therefore only works in a 5' to 3' direction.. As a consequence, one strand is replicated continuously and is known as the leading strand.

Question 29

What is stage 5 of DNA replication ?

Answer 29

The other is synthesised in fragments in the opposite direction and is known as the lagging strand.

Question 30

What is stage 6 of DNA replication ?

Answer 30

These fragments are then joined together by the enzyme ligase

Question 31

What is the source of energy of DNA replication ?

Answer 31

ATP

Question 32

When a long chromosomes is being replicated how do these events occur?

Answer 32

Simultaneously at several replication forks along its length

Question 33

What is DNA polymerase ?

Answer 33

Enzyme which adds free nucleotides to the 3' end of a growing strand

Question 34

What is DNA ligase ?

Answer 34

Enzyme that joins fragments of DNA together to form a long continuous strand

Question 35

What is the lagging strand ?

Answer 35

Strand of DNA replicated in fragments which must be joined together

Question 36

What is the leading strand?

Answer 36

New segment of DNA replicated continuously from template DNA

Question 37

What is a primer ?

Answer 37

Small sections of DNA/nucleic acid, complimentary to the template strand, which allows DNA polymerase to start replication

Question 38

Describe the semi-conservative replication theory?

Answer 38

Each daughter DNA molecule made in DNA replication will consist of half the original strand plus half a newly synthesised strand