Tumour supressor genes Flashcards
What were the initial thoughts against and in favour of tumour suppressor genes existing?
YES- loss of growth suppressor genes more likely than a gain of function mutation in ras
NO- losing both copies of the suppressor gene seems unlikely
Features of familial retinoblastoma?
usually bilateral- affects both eyes
recessive disease
significant increase in non-retinal tumours
diagnosed very early on in life
How did knudson collect data to create the 1/2 hit hypothesis?
Collected data from patients with both unilateral/sporadic and bilateral/familial RB over many years
plotted % of cases not yet diagnosed against age in months
made a log scale to determine how many ‘reactant’ were involved in each form of the disease
What does a straight and curved line mean in a log plot?
Straight=one thing involved
Curved= two things involved
What was determined about unilateral RB?
It takes two independent events to form
the genome needs 2 hits
What was determined about familial RB?
It only takes one event to form
the genome only needs one hit
If it takes two hits, why is sporadic RB at such a high frequency?
Homologous recombination and subsequent segregation of the chromatids causing loss of heterozygosity
What is homologous recombination?
Occurs during G2 and M
sister chromatid arms can wrap around each other and swap over
transferring (for example) a mutated gene from one chromosome to another
depending on the segregation of the chromatids into the daughter cells- the cells may lack any functional copy of the gene
What other events cause loss of heterozygosity?
Gene conversion
Chromosomal disjunction
What is gene conversion?
When DNA replication temporarily switches from one template to another- possibly synthesizing a mutated allele
What is chromosomal disjunction?
When both chromatids of a chromosome move into a daughter cell, meaning the other daughter cells lacks a chromosome
What is D esterase?
An enzyme that hydrolyses esters
there are 2 alleles, both code for proteins of different lengths which can thus be separated through gel electrophoresis
Where is the gene D esterase positioned?
Chromosome 13 on the q arm in region 14
What is zymography?
Technique- based on gel electrophoresis- method for measuring enzymatic activity
no denaturation of proteins
the gel is impregnated with a substrate of the proteins which are separated
if there is interaction- this will be detected
two bands on a zymogram signified heterozygosity
What does the zymogram of a patient with RB always show?
Homozygosity of the d esterase gene
