24 Flashcards
what are the three types of mutations that can occur
- point mutation
- frameshift mutation
- chromosomal mutation
what does AUG code for
methionine (start codon=
its the only aa with only one code
what are the stop codons
UAA
UGA
UAG
what are the three types of point mutations
- silence
- missense (conservative and non conservative)
- non sense
diseases linked with missense mutations
sickle cell anaemia, colorectal cancer
diseases linked with nonsense mutations
beta thalassemia, mcardles disease
Whats the mutation causing sickle cell anaemia
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.
HT disease mutation
trinucletoide repeat expansion where CAG motif is repeated more than 40times when it should normally be repeated 10-15 times
CF mutation
deletion of deltaF508 gene
What is a frameshift mutation
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
disease frameshift mutation
tay sachs disease.
mutation in beta hexosaminidase A (Hex-A)
most are point mutations bs 8 frameshift mutations 6 deletions 2 insertions
what are the 4types of chromosomal aberrations with explanation and diseases
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)
cri du chat
Partial deletion of the short arm of chromosome 5 (5p) (as in the region above the centromere)
90% are sporadic and de novo deletions
di George syndrome
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
Charcot marie tooth
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
Heritable neuropathy liable to pressure palsy HNPP
deletion of CMT1A
XX male syndrome
Translocation of SRY gene from Y chromosome to X chromosome
what is nondisjunction
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)
turners syndrome
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
klinefelter syndrome
47 chromosomes (XXY sex chromosomes) Only affects male Sx: Female type pubic hair patter, small testes, poor beard growth, chest development in 30% cases
what are the two causes of genetic mutations
spontaneous (error)
induced (env)
eukaryote error rate
10^-4 —-> 10^-6
what is the origin of spontaneous mutations
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
mutagens include radiation. what are the two types of radiations
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
