Keeping The Genome In Good Shape

Question 1

Why are somatic mutations more common than germline mutations?

Answer 1

In evolutionary terms the soma is less important than the germline because it is not passed on to new geenrations. Thus, more energy is expended by the cell In DNA repair of the germline that is expended in DNA repair of the soma

Question 2

How many mutations, minimum, are usually required for cancer development?

Answer 2

Over 10

Question 3

Why is colon cancer so common?

Answer 3

Cells in the colon are rapidly dividing and so they are replicating their DNA more often than other cells give more opportunity for mutations to occur

Question 4

What is the name of the enzyme which unzips the double helical structure of DNA during replication?

Answer 4

DNA helicase

Question 5

What is the name of the enzyme which replicates DNA?

Answer 5

DNA polymerase

Question 6

What is DNA mismatch?

Answer 6

A replication error where one base is incorrectly paired resulting in a distortion of the double helical structure

Question 7

What molecule picks up on DNA mismatch and bind to the incorrect pairing?

Answer 7

DNA mismatch repair complex

Question 8

In the repair of DNA mismatch what enzymes removes nucleotides from the mistake onwards so that DNA polymerase can rewrite this part of the sequence?

Answer 8

DNA exonuclease

Question 9

Give examples of mutagens

Answer 9

Free radicals
Diet
Chemical exposure
Smoking
Radiation exposure

Question 10

What kind of DNA mutation do X rays cause?

Answer 10

Double stranded breaks

Question 11

What kind of mutation does UV light cause?

Answer 11

Thymidine dimerisation

Question 12

Describe the process of nucleotide excision repair

Answer 12

The NER multienzyme complex binds to the mutated region to mark where DNA endonuclease should work
DNA endonuclease then cuts DNA within a sequence to make a single stranded break that removed the damaged sequence
DNA polymerase then reforms DNA

Question 13

Defects in the nucleotide excision repair process are associated with which autosomal recessive diseases?

Answer 13

Xeroderma pigmentosum

Cockayne syndrome

Question 14

What are the symptoms and complications of xeroderma pigmentosum?

Answer 14

Predisposition to light induced skin lesions and cancer
Accelerated ageing
Dwarfism
Neurological disabilities

Question 15

What are the symptoms and complications of cockayne syndrome?

Answer 15

Accelerated ageing
Dwarfism
Neurological abnormalities
Predisposition to light induced skin lesions and cancer

Question 16

What are the two processes by which double stranded breaks can be repaired?

Answer 16

Non homologous end joining

Homologous end joining

Question 17

Describe homology dependent repair of double stranded breaks

Answer 17

DNA endonuclease is used to peel back some of the DNA sequence on either side of the break and this is then compared to the homologous chromosome and information is copied from this homologous chromosome or sister chromatid so that no information is lost

Question 18

In what cells is non homologous end joining more common?

Answer 18

Somatic cells

Question 19

Describe the process of non homologous end joining

Answer 19

The two strands are merged together until a homologous region id found and the ‘extra’ DNA is then cleaved by DNA exonuclease

Question 20

Why does non homologous end joining almost always lead to mutation?

Answer 20

It is non conservative and so genes are almost always lost

Question 21

Explain how repair of double stranded breaks can result in translocatiom

Answer 21

In non homologous end joining it is possible that if more than one chromosome suffers a break that two strands from different chromosomes are joined together in the repair process

Question 22

What condition results from the Philadelphia translocation?

Answer 22

Chronic myelogenous leukaemia

Question 23

Which genes from which chromosomes are combined in the Philadelphia translocation?

Answer 23

The ABL gene from chromosome 9 which promotes cell cycle progression
The BCR gene from chromosome 22 which acts as a promoter in leukocytes

Question 24

What is Nijmegen breakage syndrome?

Answer 24

A rare autosomal recessive condition where there is defective homology dependent repair which results in immunodeficiency and radiation sensitivity

Question 25

Inherited breast and ovarian cancer are autosomal dominant inherited predisposition ps towards these cancers. Mutations in what genes causes this?

Answer 25

The BRCA1 and BRCA2 genes involved in homology dependent reapir