Structure and Replication

Question 1

What shape is DNA?

Answer 1

Double Helix

Question 2

Guanine is joined to ? by ? Hydrogen Bonds

Answer 2

Guanine is joined to Cytosine by 3 Hydrogen Bonds

Question 3

Adenine is joined to ? by ? Hydrogen Bonds

Answer 3

Adenine is joined to Thymine by 2 Hydrogen Bonds

Question 4

What are adjacent deoxyribose sugars joined by?

Answer 4

Phosphodiester bonds

Question 5

What do Histones do?

Answer 5

They DNA to be supercoiled around them and packaged into chromosomes

Question 6

What base is different in RNA?

Answer 6

Uracil replaces Thymine

Question 7

Why does RNA form secondary structures?

Answer 7

Due to the complementary base pairing between bases on the same single strand

Question 8

How many strands does RNA have?

Answer 8

1

Question 9

DNA replication is said to be…

Answer 9

Semi-conservative. This is because each new double stranded molecule contains an original strand and a newly synthesised complementary strand.

Question 10

What enzymes are responsible for unwinding DNA?

Answer 10

DNA Helicases

Question 11

What stabilise the denature DNA?

Answer 11

Single Stranded Binding Proteins

Question 12

What enzyme is responsible for synthesising a short RNA Primer?

Answer 12

DNA Primase

Question 13

What enzyme is responsible for carrying out the elongation of the new strand of DNA?

Answer 13

DNA Polymerase. This occurs through complementary base pairing to the template strand

Question 14

Which direction is DNA synthesised?

Answer 14

5’ to 3’

Question 15

What is needed for the addition of the next nucleotide to initiate replication?

Answer 15

A free 3’ OH. This is supplied by the short RNA primer binding.

Question 16

Which DNA Polymerase carries out DNA replication in Eukaryotes?

Answer 16

DNA Polymerase III

Question 17

Synthesis requires…

Answer 17

A pool of all 3 dNTPs (bases)

Question 18

DNA Polymerase III catalyses…

Answer 18

the formation of a new phosphodiester bond.

Question 19

How is the speed of replication increased?

Answer 19

The replication fork moves in two directions.

Question 20

What are Okazaki Fragments?

Answer 20

Short, newly synthesised DNA fragments that are formed on the lagging template strand during DNA replication. They replace RNA Primers

Question 21

What enzyme replaces RNA Primers with Okazaki Fragments on the Lagging Strand?

Answer 21

DNA Polymerase I

Question 22

Which enzyme seals the gap between OKazaki Fragments?

Answer 22

DNA Ligase

Question 23

What is the error frequency of nucleotides inserted into the growing DNA strand?

Answer 23

1 in 100,000 (10^5)

Question 24

What is the error frequency of the polymerase enzyme’s 3’ to 5’ editing function?

Answer 24

1 in 100 (10^2)

Question 25

After a further check for mismatched bases, what is the overall error frequency of DNA replication?

Answer 25

1 in 10^9

Question 26

What causes mutation?

Answer 26

DNA Damage. This can be due to Radiation or certain chemicals. This are known as mutagens. Most carcinogens are mutagens

Question 27

What types of mutations are there?

Answer 27

Base Substitutions. Deletion of bases. Insertion of bases. Rearrangement of bases.

Question 28

Which type of mutations can be described as silent?

Answer 28

Substitutions because the triplet code may still code for the same amino acid.

Question 29

A mutation in which type of cell can be inherited?

Answer 29

Germ Cell

Question 30

A mutation in which type of cell cannot be inherited but could lead to cancer?

Answer 30

Somatic Cell

Question 31

What types of proteins remove damaged bases?

Answer 31

Base Excision Repair Proteins. They are specific to specific types of damage

Question 32

What types of proteins remove sections of damaged DNA strands?

Answer 32

Nucleotide Excision Repair Proteins. They are less specific and cut out whole sections.

Question 33

After damaged sections removed by either Base or Nucleotide Excision Repair Proteins, how is the DNA repaired.

Answer 33

DNA Polymerase I replaces the DNA by copying the intact strand and DNA Ligase seals the gaps.

Question 34

In terms of DNA repair, when might mutations occur?

Answer 34

If the repair goes wrong or there is too much damage to repair. This increases the chance of cancer.

Question 35

Which enzyme recognises the irregular presence of Uracil in a DNA strand and removes it?

Answer 35

Uracil N-Glycosylase

Question 36

Why may there be Uracil in DNA?

Answer 36

Because the deamination of cytosine produces uracil, which base pairs with adenine.