Mutations

Question 0

Describe point mutations

Answer 0

Base subsitution - transition e.g. Purine to purine, transversion purine to pyrimidine

Can be silent - doesnt alter aa
Missence - replaces aa
Nonsence - changes aa to stop

Question 1

Explain the relationship between changes kn nucleotide and amino acid sequence

Answer 1

Change in sequence of nucleotides xan change the amino acid that is coded for
Change in primary sequence of aa can change protein

Question 2

Describe insertion/deletion mutations

Answer 2

Addition/subtraction of multiple of 3 nucleotides - no frameshift
Addition/subtraction of multiple not of 3 - frameshift

Question 3

Describe how spontaneous mutations may occur

Answer 3

Sequence changes during DNA base replication

• rare tautomeric forms with altered base pairing
• DNA strand slippage during replication

Question 4

Describe how induced mutations may occur

Answer 4

Chemical mutagens - alter bases or disrupt base stacking

Radiation - UV light causes adjacent thymine to bind

Question 5

What is meant by wild type?

Answer 5

An individual within a population displacing a wild type trait, which is the trait most common in the population

Question 6

Name the 3 types of DNA repair

Answer 6

Mismatch repair
Excision
Double strand break

Question 7

Describe mismatch repair

Answer 7

Inserted nucleotide is recognised and replaced

Question 8

Describe DNA base excision

Answer 8

Either base or nucleotide excision

Repair of single-stranded DNA damage caused by externa, agents lr endogenous factors (ROS)

Question 9

Describe the process of double strand break repair

Answer 9

Both DNA strands are broken and chromosomes are re-arranged

Question 10

Explain relationship between DNA damage and cancer

Answer 10

Mutation of mismatch repair enzymes means DNA not repaired

Tumour forms due to growth advantage conferred on cells which aquire 6 new capabilities

Question 11

List the 6 new capabilities of tumour cells

Answer 11

• divide indipently of external growth signals
• ignore external anti-growth signals
• avoid apoptosis
• divide indefinitely without senescence
• stimulate sustained angiogenesis
• invade tissues and establish secondary rumours

Question 12

What are oncogenes

Answer 12

Genes involved incontrol of cell division - may stimulate/inhibit

Question 13

What is the function of tumoursuppressor?

Answer 13

Genes involved in protecting the cell against cancer

Question 14

Why is PCR so important in diagnosising genetic disease?

Answer 14

Most mutations are single base - hard to detect
PCR amplifies fragments so they can be used in other tests

E.g. In sickle cell restriction site for enzyme MstII destroyed -> with gel electrophoresis and southern blotting the mutated gene will have less DNA fragments as the restricition site is no longer there

Question 15

What mutations is southern blotting used to detect?

Answer 15

Used to analyse larger segments of DNA within and around a gene
-analyse triple repeat disorders e.g. Huntingtkns, fragile X

Question 16

What mutations is ‘array comparative genomic hybridaisation’ used to detect?

Answer 16

Used to screen for submicroscopic chromosomal deletions for which the locus cannot be deduced from phenotype

Question 17

Describe the process of array CGH

Answer 17

1) array of DNA probes covering entire genome applied to surface of solid matrix
2) patient DNA and normal control DNA are each labelled with different coloured flourescent tags e.g. Patient red and normal green
3) equal amounts of labelled DNA hybridised to probe array and hybridaisation signals detected and compared
4) for probes where signal of normal DNA >patients DNA the patient has a deletion of the chromosomal region from which that probe was derived