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MGD > Mutagenesis > Flashcards

Mutagenesis Flashcards

1
Q

What is a transition mutation?

A

Purine to purine or pyrimidine to pyrimidine

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2
Q

What is a transversion mutation?

A

Purine to pyrimidine or pyrimidine to purine

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3
Q

What are the pyrimidines?

A

Thymine and cytosine (uracil in mRNA)

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4
Q

What are the purines?

A

Adenine and guanine

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5
Q

What 4 types of mutation can occur?

A

Non sense
Silent
Missense
Frameshift

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6
Q

What do mutations in non coding areas commonly cause?

A

Alterations in binding sites, promotor sites and splice sites

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7
Q

What do mutations at splice sites usually result in?

A

Skipping of exon immediately adjacent to mutation

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8
Q

After mutations at splice sites what happens if the exon is/isnt a multiple of three?

A

Is- mRNA shortened but remain in frame, could disrupt the function of the protein as shape may change
Isnt- mRNA will be shortened and will contain a frameshift and PTC leading to nonsense mediated decay.

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9
Q

Why does the exon skipped in splice site mutations not being a multiple of three often lead to a better outcome?

A

The mutated protein will be destroyed and not cause any disruption.

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10
Q

What can insertion/deletion of bases cause and when?

A

Frameshift, when they arent inserted/deleted in multiples of three base pairs.

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11
Q

What is a silent mutation and when can they still be problematic?

A

A mutation that doesnt alter the aa coded for (due to the genetic code being degenerate)
Can disrupt RNA splicing eg by introducing another splicing site which can still cause heritable diseases.

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12
Q

What is a missense mutation?

A

A mutation that replaces one aa with another, usually by a single base change.

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13
Q

What is a nonsense mutation and what can it cause?

A

A mutation that changes the aa coded for to a stop codon. Shortens protein and causes a premature stop codon (PCT)

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14
Q

What is a frameshift mutation, when can they occur and what can they cause?

A

Addition or subtraction of nucleotides not in multiples of three so the reading frame of mRNA is altered. Eg insertions, deletions, splice site mutations. Can create premature stop codons (PTC)

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15
Q

What is the protective mechanism against PTCs?

A

mRNA containing these are degraded by nonsense mediated decay and little or no protein is produced.

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16
Q

What causes spontaneous mutations?

A

Errors in DMA replication

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17
Q

What are two examples of spontaneous mutation?

A

Tautomeric shift

Slippage

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18
Q

What is tautomeric shift?

A

The 4 bases can undergo tautomeric shift where a proton briefly changes position. Tautomeric forms cause c to bind to a and g to bind to t. If c is in its rare tautomeric form DNA polymerase recognises it as t and an a will be inserted into the new strand.

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19
Q

What is slippage?

A

2 things can cause it:
A nucleotide can be added to the newly synthesised strand to lengthen it or a nucleotide can be omitted from the template strand so the newly synthesised strand will be one base shorter.

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20
Q

What does the rate of spontaneous mutation depend on?

A

Size

Sequence

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21
Q

What two ways can you cause a PTC?

A

Non sense mutation

Frameshift

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22
Q

What can cause induced mutations?

A

Chemicals

Radiation

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23
Q

What are chemicals that are cause mutations (mutagenic)/cause cancer (carcinogenic) called?

A

Mutagens/carginogens

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24
Q

What does ionising radiation do?

A

Produces ions when it interacts with cellular molecules.

25
Q

What are two examples of ionising radiation?

A

Xrays

Uv radiation

26
Q

When may aa subs be better tolerated?

A

If they have similar structures or properties

27
Q

What is a mutation?

A

A change in the nucleic acid sequence which can be due to insertion, deletions or the rearrangement of several nucleotides

28
Q

What is a wild-type?

A

The trait that is most common in the population.

29
Q

What does a mutation do in relation to the wild-type?

A

Causes a mutant phenotype that differs from the wild-type in the population.

30
Q

What does a mutation in a gene do in relation to the wild type allele?

A

Causes a mutant allele that differs from the wild type allele

31
Q

What is a consequence of mutations in the germline?

A

Possibility of it being passed onto offspring

32
Q

What two ways can DNA be repaired?

A

Mismatch repair

Excision repair

33
Q

What happens in mismatch repair?

A

enzymes detect nucleotides that dont base pair in newly replicated DNA. The incorrect base is excised and replaced (proof reading)

34
Q

What happens in excision repair? (Two types)

A

Damaged DNA is removed by excision of bases and replacement by DNA polymerase.
Nucleotide excision repair replaces upto 30 bases and is used in repair of UV damage and come carcinogens.
Base excision repair replaces 1-5 bases and repairs oxidative damage.

35
Q

What protein monitors repair of damaged DNA and what can it do?

A

P53, can promote apoptosis if the damage is too severe.

36
Q

What is apoptosis?

A

Programmed cell death

37
Q

How are cancerous cells produced?

A

(Failure of DNA repair mechanisms). If apoptosis doesnt occur or the damage to DNA leads to uncontrolled growth.

38
Q

What are the 6 new characteristics of tumours?

A

Divide independently of external growth signals.
Ignore external anti growth signals.
Avoid apoptosis.
Divide indefinitely.
Stimulate sustained angiogenesis.
Invade tissues and establish secondary tumours.

39
Q

What do tumours arise from?

A

Lack of normal growth control.

40
Q

When are tumours more likely to arise?

A

From cell types undergoing frequent cell division

41
Q

What is similar about all the cells in a tumour and what does the behaviour of the tumour depend on?

A

They are all the same type of cell. Depends on the cell type.

42
Q

What does it mean if a mutation is inherited?

A

All cells carry one mutation therefore the probability of a second mutation to cause a tumour is higher.

43
Q

What does it mean if a mutation is sporadic?

A

You only have a somatic mutation in one cell therefore the chance of a second mutation in the same cell is lower.

44
Q

What do inherited cancer genes tend to be and how will they be expressed?

A

They tend to harbour recessive mutations but development of cancer displays dominant pattern. Therefore for initiation of tumour both copies of the gene must be mutated or the wild type copy must be deleted.

45
Q

What are oncogenes, what are they in normal cells and what do they do?

A

Genes involved in control of cell division. They are proto-oncogenes in normal cells and they may stimulate/inhibit growth.

46
Q

What are tumour suppressor genes?

A

Involved in protecting the cell against one step on the path to cancer.

47
Q

When do proto-oncogenes become oncogenes?

A

When there is a mutation or increased expression

48
Q

What can carry copies of oncogenes?

A

Viruses

49
Q

What is needed if we want to investigated mutations as they are often single base changes that are hard to detect?

A

PCR to amplify the sample.

50
Q

Whats are 2 examples of conditions that use PCR to investigate and what happens after that?

A

Sickle cell where the restriction site for MstII is destroyed. Amplify with PCR and then Gel electrophoresis/southern blotting will show less DNA fragments for this section of DNA if its digested with MstII.
CF has a three base deletion so you can observe how the length of the DNA is different with the techniques above.

51
Q

How can you get a DNA sample from a foetus?

A

Amniocentisis

Chorion villus biopsy

52
Q

What happens in amniocentisis?

A

15-20 wks into gestation.
Under ultrasound guidance.
Cells once collected can be cultured in presence of mitotic stimulus to amplify sample.
0.5-1% risk of miscarriage.

53
Q

What happens in chorion villus biopsy?

A 
10-13 wks into gestation.
Under ultrasound guidance.
Transcervical/transabdominal
Foetal villi must be separated from maternal tissue as may be cosampled at the same time.
2% risk of causing miscarriage.
54
Q

What do osteogenesis imperfecta and duchennes muscular dystrophy have in common?

A

The arise due to whole exon duplications/deletions

55
Q

What does MLPA stand for and what can it be used for?

A

Multiplex ligation-dependent probe amplification.

Count the copy number for many exons in parallel.

56
Q

What is used for MLPA?

A 
For a short sequence of DNA, 2 adjacent probes are designed, one containing a forward primer and one containing a reverse primer.
In addition, one of the probes contains a stuffer sequence so the length can be varied.
The probes are hybridised against the target DNA.
If the probes manage to bind to the real target DNA they will bind adjacently and they can be ligated to produce a functional PCR strand.
Therefore ligation (and then amplification) can only occur if the sample DNA is there.
57
Q

How can MLPA samples be used?

A

The amount of PCR product is proportional to the amount of target DNA so can be used as a quantitive measurement.
When the samples are compared with a control, seeing a peak that is half the height of the controls (half the amount of PCR product has been produced) shows there has been a deletion.

58
Q

What determines the consequence of a mutation?

A

The type and the location within the gene.

MGD (3 decks)

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