Mutations

Question 1

In terms of base substitution what is the difference between a transition and a transversion?

Answer 1

Transitions are between two of the same, e.g. Between two purines and transversions are between a purine and a pyrimidine

Question 2

Where will a single base substitution cause no change?

Answer 2

If it occurs in the third position.

Question 3

What is a missense mutation?

Answer 3

This is where one amino acid is substituted for another usually caused by a single base substitution.

Question 4

What is a silent mutation?

Answer 4

This is where there is a single base substitution but it has no effect on the amino acid.

Question 5

What is it called when an amino acid codon is changed for a stop codon?

Answer 5

Nonsense mutation

Question 6

What is a frame shift mutation?

Answer 6

This is where the reading frame of RNA is altered due to an insertion, deletion or due to a mutation of the split site. These commonly result in premature stop codons being present.

Question 7

What can be said about a conservative missense mutation?

Answer 7

This is where the two amino acids which have been substituted are very similar and therefore have little effect on protein function.

Question 8

What insertions/deletions do not disrupt the reading frame?

Answer 8

When they are a multiple of three base pairs.

Question 9

What happens to mRNA with premature stop codons?

Answer 9

It is broken down by nonsense mediated decay to prevent protein being produced.

Question 10

What happens when a promter, stop or start codon mutation occurs at a splice-site?

Answer 10

When this happens, the impact depends on whether the exon which is skipped has a multiple of three base pairs. It can actually be more dangerous if it does have because this means that it will not be degraded.

Question 11

What is tautomeric shift?

Answer 11

This is where protons on the four bases can briefly change position. This leads to alternative base pairing.

Question 12

Explain what the effect on a DNA strand in replication can be as a result of slippage.

Answer 12

This can either result in an addition base on the new strand if slippage occurs on the new strand or omission of a base if slippage occurs on the old strand.

Question 13

What two ways can chemicals cause mutations in DNA?

Answer 13

Directly alter DNA bases, or disruption DNA base packing.

Question 14

What two chemicals can alter DNA base pairing?

Answer 14

Nitrous acid replaces amino groups with Keto groups and this affects the pairing of all bases. Ethyl methane sulphonate (EMS) removes purine rings which leads to apurinic sites which can then pair with any base.

Question 15

How is DNA base stacking interrupted?

Answer 15

IQ is a food mutagen found in meat and cigarette smoke. This impacts how RNA polymerase sees the strand, and this results in single base deletions at GC groups.

Question 16

What environmental factor can lead to DNA mutation?

Answer 16

Exposure to radiation, UV, X-RAY, radon gas….

Question 17

Why is it important for the body to have DNA repair mechanisms?

Answer 17

This is important because mistakes are common. Most errors are corrected immediately by DNA polymerase.

Question 18

What is nucleotide mis-match repair?

Answer 18

This is where enzymes detect mismatched bases and they are replaced along with a patch of DNA sequence.

Question 19

What process is used to replaced damaged bases in a DNA strand?

Answer 19

Excision repair.

Question 20

What disease is a result of failure of DNA repair systems?

Answer 20

Cancer.

Question 21

State some of the characteristics a cell must have in order to produce tumours.

Answer 21

It must be able to divide independently of external growth signals, ignore anti growth signals, avoid apoptosis, divide indefinitely, be able to obtain nutrients from capillaries, invade tissues and establish secondary tumours.

Question 22

what genes are commonly affected in breast cancer?

Answer 22

BRCA1 and 2. These affect the proteins responsible for checking for DNA mutations at checkpoints in the cell cycle. Without this occuring cells with mutations are produced.

Question 23

What is an oncogene?

Answer 23

This is a gene which can transform a cell to a cancerous phenotype.

Question 24

Are proto oncogenes harmful?

Answer 24

Generally no, they perform a variety of cell functions. They can however be activated into cancer causing oncogenes.

Question 25

Explain why sporadic cases of cancer are unlikely.

Answer 25

Cancer is generally caused by a recessive mutation. For those who have one affected allele, they are more likely to gain one mutation in their non faulty gene than a non carrier is to gain two mutations.

Question 26

What is the most common form of mutation in DNA?

Answer 26

Single base substitution.

Question 27

What can be said about an individual with cystic fibrosis given that the mutation can occur anywhere along the gene?

Answer 27

This means that they can be a compound Heterzygote because they have two different mutations.

Question 28

What is SSCP mutation scanning?

Answer 28

This is a process to identify a mutant portion of DNA so that targeted sequencing can be done. DNA is heated and cooled and this leads to the single strand adopting partially double stranded forms which are then separated.

Question 29

What are two methods for obtaining fetal DNA?

Answer 29

Amnio centesis where a needle is inserted through the tummy under ultrasound guidance and Chorionic Villus which can be trans cervical or trans abdominal.

Question 30

What is the purpose of MLPA?

Answer 30

MLPA allows us to count copy numbers and therefore we can identify if a mutation occurs on both strands or just a single strand of DNA.

Question 31

In MLPA what is used so we can identify how much DNA is affected by mutation?

Answer 31

A stuffer. This gives the DNA strands different lengths so we can identify them.