Gene Mutations

Question 1

What is a gene mutation?

Answer 1

an alteration in the nucleic acid sequence of the genome of an organism

Question 2

How do gene mutations arise?

Answer 2

• Errors during replication
• Mutagens

Question 3

What errors occur during replication?

Answer 3

• Point mutations
• Replication slippage

Question 4

What does Ultraviolet cause?

Answer 4

• causes dimerization of adjacent pyrimidine bases (esp thymines)= deletion mutation

Question 5

What is dimerization?

Answer 5

the process of joining two identical or similar molecular entities by bonds

Question 6

What does ionising radiation cause?

Answer 6

Electromagnetic waves and particles= direct and indirect damage

Question 7

What is an example of indirect damage caused by ionising radiation?

Answer 7

Free radicals which attach to DNA strand and break pieces off

Question 8

What chemicals are classed as mutagens?

Answer 8

asbestos
cyanide
alcohol
sawdust
disinfectant

Question 9

What are the general approaches against mutation?

Answer 9

1- Prevent
2- Repair
3- Give up (apoptose the whole cell)

Question 10

What does prevent involve?

Answer 10

• Melanin (protect DNA in skin)
• Peroxisomes (an organelle that makes antioxidant enzymes)
• Good life choices

Question 11

What does repair involve for Nicks? (mutagens)

Answer 11

phosphodiester bond breaks which DNA ligase repairs

Question 12

What does repair involve for single stranded damage to bases? (mutagens)

Answer 12

base excision repair for small bits of damage and nucleotide excision repair for big bits of damage

Question 13

What does Polymerase III do to repair mutations caused during DNA replication?

Answer 13

Proofreading activities

Question 14

What other form of repair is there if mutation is caused by DNA replication?

Answer 14

Mismatch repair, 4 proteins detect lack of hydrogen bonds between mismatched base pairs, and then repair

Question 15

What 4 proteins are involved in mismatch repair?

Answer 15

MSH2
MSH6
MLH1
PMS2

Question 16

Why is giving up sometimes the best option?

Answer 16

There may be too many mutations for cells to repair
Apoptosis (programmed Cell death) is initiated

Question 17

Examples of giving up

Answer 17

• Sunburn with blistering
• Radiotherapy treatment
• Radiation sickness

Question 18

How does the location of mutation affect outcome?

Answer 18

Non-coding= no affect
Coding= potential for effect

Question 19

What is frameshift?

Answer 19

Shifts reading frame (rest of protein effected), caused by insertion or deletion of non multiples of 3

Question 20

What is a silent mutation?

Answer 20

different base, but still codes for the same amino acid so no effect

Question 21

What is a Missense mutation?

Answer 21

changes to a different amino acid, only affects one amino acid so small effect especially if similar shape/ charge

Question 22

What is a nonsense mutation?

Answer 22

changes codon to a stop codon, big effect if at start of protein

Question 23

How can a mutation cause cancer?

Answer 23

Mutation in gene that normally controls cell division
oncogenes or tumour supressor genses= potential to cause cancer

Question 24

What are Germline cells?

Answer 24

cells in body that make sperm and eggs

Question 25

What are somatic cells?

Answer 25

All other body cells

Question 26

How can a mutation effect the phenotype of offspring?

Answer 26

If mutation occurs on a relevant protein and in a germline cell= potential to change phenotype of offspring
Could be harmless change or cause a genetic disease
Possibility for selective advantage

Question 27

What is Cystic Fibrosis?

Answer 27

Autosomal recessive condition
Caused by one of many mutations in gene encoding the CFTR protein

Question 28

What is CFTR?

Answer 28

cystic fibrosis transmembrane conductance regulator

Question 29

What does CFTR do?

Answer 29

Is a membrane protein that transports chloride ions

Question 30

What happens if CFTR is defective?

Answer 30

Cl ions cannot exit cells
Sodium (thus water) follow Cl out of mucus into cell
Less water in mucus
thick mucus= recurrent infections

Question 31

What is Neurofibromatosis (NF)?

Answer 31

Autosomal dominant
Caused by a mutation in one of 2 genes

Question 32

In what protein can mutations occur to cause NF

Answer 32

Neurofibrin protein= NF1
Merlin protein= NF2

Question 33

What do NF1 & NF2 proteins control?

Answer 33

Control cell cycles as “tumour suppressor genes”

Question 34

What is the most common tumour for NF1?

Answer 34

Neurofibromas

Question 35

What is the most common tumour for NF2?

Answer 35

Schwannomas

Question 36

What is Phenylketonuria?

Answer 36

Autosomal recessive
Caused by mutation in the gene coding for the protein phenylalanine hydroxylase

Question 37

What is phenylalanine hydroxylase responsible for?

Answer 37

This enzyme is responsible for metabolising the amino acid phenylalanine

Question 38

Why is phenylketonuria variable?

Answer 38

Very dependant on early dietary modification
If phenylalanine free diet= near normal phenotype
If phenylalanine rich diet= build up in brain

Question 39

What is Huntington’s Disease?

Answer 39

Autosomal dominant
Caused by increased CAG repeats in the gene that codes for huntingtin protein

Question 40

What is the huntingtin protein normally involved in?

Answer 40

Usually involved in transport along neronal axons

Question 41

Is Huntington’s disease variable and what are some symptoms?

Answer 41

-YES
progressive inability to control body movements
Change in mood/ personality
Symptoms are more severe and onset earlier with more CAG repeats
More CAG repeats occur with each generation