DNA replication

Question 1

DNA has two principal functions

Answer 1

Template for DNA replication
Template for RNA replication

Question 2

Why is DNA considered semi conservative

Answer 2

One new daughter strand is synthesised with each round of DNA replication so it is reused

Question 3

What is a replication fork

Answer 3

Both strands of the template DNA are replicated at the same time. So split

Question 4

What is leading strand

Answer 4

Synthesised continuously in direction of the fork

Question 5

What is the lagging strand

Answer 5

Synthesised discontinously against the replication fork

Question 6

DNA replication process

Answer 6

1. Helicases unwind the parental double helix
2. Single strand binding proteins stabilise the unwound parental DNA
3. The leading strand is synthesised continuously by DNA polymerase
4. The lagging strand is synthesised discontinously formed by Okazaki fragment
5. After the RNA primer is replaced by DNA. DNA ligase joins the Okazaki fragment to the growing strand

Question 7

What does DNA polymerase do

Answer 7

Synthesise the DNA in the 5-3 direction
Needs a primer to start

Question 8

What does DNA polymerase use to add nucelotides

Answer 8

3 OH groups

Question 9

DNA polymerase creates new strand in what direction

Answer 9

3-5 direction

Question 10

What are the DNA fragments called

Answer 10

Okazaki fragments

Question 11

What enzyme removes the RNA primers

Answer 11

Exonuclease enzyme

Question 12

Are both strands synthesised at the same time

Answer 12

Yes

Question 13

What contributes to telomere shortening

Answer 13

Short segment of DNA

Question 14

Endogenous damaging agents

Answer 14

Errors in replication
Reactive oxygen species
UV radiation from the sun
X-rays and gamma rays
Mutagenic chemicals

Question 15

Healthy cells are able to respond to DNA damage by

Answer 15

Repairing the DNA using cells DNA repair mechanism
Apoptosis

Question 16

Gene mutations will arise when

Answer 16

DNA damage

Question 17

Silent mutations definition

Answer 17

Will have no effect on the protein

Question 18

Missense mutation definition

Answer 18

Result in the incorporation of the wrong amino acid

Question 19

Nonsense mutation definition

Answer 19

Results in a stop codon hence a premature codon

Question 20

Frameshift mutation definition

Answer 20

Changes the frame of protein translation

Question 21

Endogenous DNA damage results in

Answer 21

Base loss
The glycosyl bond linking DNA bases with deoxyribose is labile
When DNA is replicated causes by deletions, can cause breaks

Question 22

Base modifications involve

Answer 22

Deamination
Oxidation by ROS

Question 23

Deamination is when

Answer 23

Amino groups of nucleic acid bases are unstable and are lost

Question 24

Oxidation by ROS is when

Answer 24

Reactive oxygen species result from oxidative metabolism and ionising radiation
Produces hyperactive oxygen can modify nucleotides
Causes point mutations when replicated
Common one is G-T

Question 25

Effects of exogenous DNA damage

Answer 25

Methylation
Inter strand cross links

Question 26

Methylation

Answer 26

Many environmental chemicals, can modify DNA bases, by addition of a methyl or alkyl group

Question 27

Interstrand cross links

Answer 27

By attaching to bases on both strands, alkylating agents can cross link both strands

Question 28

UV light causes what

Answer 28

Photodamage

Question 29

Ionising radiation causes

Answer 29

Single strand and double strand breaks
Breakage of chromosomes can cause translocations, duplications, inversions and deletions

Question 30

DNA repair mechanism

Answer 30

Recognition- detection of the damage
Incision- cutting into damaged DNA
Excision- removal of the damaged part
Polymerisation- gap filled by DNA polymerase
Religation- joining of the gaps by DNA ligase

Question 31

Cells have DNA damage response which

Answer 31

Activates G1 DNA damage checkpoint via activating p53