24

Question 1

what are the three types of mutations that can occur

Answer 1

1. point mutation
2. frameshift mutation
3. chromosomal mutation

Question 2

what does AUG code for

Answer 2

methionine (start codon=

its the only aa with only one code

Question 3

what are the stop codons

Answer 3

UAA
UGA
UAG

Question 4

what are the three types of point mutations

Answer 4

1. silence
2. missense (conservative and non conservative)
3. non sense

Question 5

diseases linked with missense mutations

Answer 5

sickle cell anaemia, colorectal cancer

Question 6

diseases linked with nonsense mutations

Answer 6

beta thalassemia, mcardles disease

Question 7

Whats the mutation causing sickle cell anaemia

Answer 7

non conservative missense mutaiton
CTC becomes CAC so GAG becomes GUG so glutamic acid (philic) becomes valine (phobic)

–> changes the properties of haemoglobin which carries O2 in the cells.

Question 8

HT disease mutation

Answer 8

trinucletoide repeat expansion where CAG motif is repeated more than 40times when it should normally be repeated 10-15 times

Question 9

CF mutation

Answer 9

deletion of deltaF508 gene

Question 10

What is a frameshift mutation

Answer 10

Where a single base is added or deleted from DNA causing a change in every amino acid in the protein after this point

can either be base insertion or base deletion

Question 11

disease frameshift mutation

Answer 11

tay sachs disease.
mutation in beta hexosaminidase A (Hex-A)
most are point mutations bs 8 frameshift mutations 6 deletions 2 insertions

Question 12

what are the 4types of chromosomal aberrations with explanation and diseases

Answer 12

Deletions: Part of a chromosome is left out (Cri du Chat, Di George Syndrome, HNPP)

Duplications (insertions): Part of a chromosome breaks off and attaches to the sister chromatid. Gives double the amount of protein so can be bad. (Charcot Marie Tooth)

Inversions: Part of a chromosome breaks off and reinserts backwards, don’t usually cause any abnormalities as long as its balanced (not halfway through a gene)

Translocations: Part of a chromosome breaks off and attaches to a different chromosome. Changes gene location on chromosome and can change the number of copies of a gene (XX male syndrome)

Question 13

cri du chat

Answer 13

Partial deletion of the short arm of chromosome 5 (5p) (as in the region above the centromere)
90% are sporadic and de novo deletions

Question 14

di George syndrome

Answer 14

Deletion of a region of long arm of chromosome 22 (22q11.2) (as in the region below the centromere)
Microdeletion of 8 genes
Majority of cases are de novo

Question 15

Charcot marie tooth

Answer 15

Most common heritable peripheral neuropathy
70-80% of cases duplication of large region of short arm of chromosome 17 (1.4Mb) 17p11.2
Includes gene peripheral myelin protein 22 (PMP22) –> duplication renders myelin on schwann cells not v effective

Question 16

Heritable neuropathy liable to pressure palsy HNPP

Answer 16

deletion of CMT1A

Question 17

XX male syndrome

Answer 17

Translocation of SRY gene from Y chromosome to X chromosome

Question 18

what is nondisjunction

Answer 18

Chromosomes fail to separate properly
Trisomy= extra chromosome (Down syndrome)
Monosomy= lack of a chromosome (only viable if X chromosome e.g. Turner’s syndrome)
Triploidy= 3 sets of chromosomes (in humans triploid babies miscarry or die within first year, in banana plants renders them sterile and needing clonal propagation)

Question 19

turners syndrome

Answer 19

45 chromosomes (X sex chromosome) –> ONLY monosomy that gives viable offsprings
Only affects females
Complete or partial loss of one sex chromosome
Sx: no menstruation, short stature, poor breast development, brown spots (nevi), constriction of aorta

Question 20

klinefelter syndrome

Answer 20

47 chromosomes (XXY sex chromosomes) 
Only affects male 
Sx: Female type pubic hair patter, small testes, poor beard growth, chest development in 30% cases

Question 21

what are the two causes of genetic mutations

Answer 21

spontaneous (error)

induced (env)

Question 22

eukaryote error rate

Answer 22

10^-4 —-> 10^-6

Question 23

what is the origin of spontaneous mutations

Answer 23

Depurination (most common): loss of a purine base (A or G)
Deamination: changes a normal base to an atypical base (C to U can be corrected) or irreparable damage: like deamination of 5-methylcytoisne and hypoxanthine
Tautomeric shift: spontaneous rearrangement of nitrogen bases allows for hydrogen bonding between mismatched base pairs
Guanine will pair with thymine rather than cytosine
Cytosine will pair with adenine rather than guanine

Question 24

mutagens include radiation. what are the two types of radiations

Answer 24

Direct
When alpha particles, beta particles or x rays create ions which physically break sugar phosphate backbone, connections between base pairs, or chemically alter bases
Bases held together by hydrogen bonds when broken: If 2 pyrimidines of the same type (T or C) are next to each other they bind to each other distorting DNA)

Indirect
Creation of free radicals where the presence of unpaired electrons damages bases or breaks backbone