mutations and cancer

what is a gene mutation and when is it likely to occur

alteration of base in primary structure, bonds with form in different places and fold differently at the tertiary structure - different 3D shape that is non functional

likely to occur in DNA replication

what can increase the frequency of gene mutations

mutagenic agents

what are the 2 mutagenic agents

high ionising radiation - x rays and gamma rays

carcinogens - chemicals like tobacco smoke, mustard gas

5 types of gene mutations

addition

detetion

substitution

inversion

duplication

addition mutation

results in a frameshift

could lead to different coding of amino acids

results in a non functioning protein

deletion mutation

frameshift to the left

could result in different polypeptide chain

non functioning protein

substitution mutation

one base has been changed for a different amino acid

no frameshift

the genetic code is degenerate so may not be an impact

inversion mutation

section of bases detach, when reattached they are inverted

code is back to front

codes for different amino acids

duplication mutation

one base is duplicated at least one

frameshift to the right

different sequence of amino acids

what does translocation of bases mean as a mutation

a section of bases detaches from chromosome and attaches to another different chromosome

impact on gene expression

results in a phenotype

how can mutations cause cancer

cancer forms by mutation of genes regulating mitosis

if genes mutate & non functioning protein made, mitosis isn’t regulated

results in uncontrollable cell growth and tumour

2 types of tumour

benign - not cancerous

malignant - cancerous

benign tumour

grows large but at a slow rate

contained in a capsule so don’t spread

non life threatening - can be removed by sugary with low likelihood of recurrence

malignant tumour

grow large rapidly

metastasis occurs - breaks off and spreads

tumour grows projections to develop it’s own blood supply

removal of tumour needs radio or chemo therapy & recurrance is more likely

oncogenes - gene mutation

oncogenes = mutated version of proto-oncogene

P-Oncogene stimulates initation of DNA replication and mitosis

oncogene mutations result in process being permanently activated making cells divide continuously

tumour supressor gene - mutation

TSG produce proteins to slow down cell division

mutation results in TSG not producing proteins & cell division would continue

mutated cells would not be identified or destroyed

abnormal methylation in TSG and oncogene

methylation causes a gene to turn on or off

hypermethylated - more methyl groups attach to TSG so it is inactivated

hypomethylated - reduced number of methyl groups attach to oncogene so gene is activated, permanently turned on (uncontrolled cell division)

increased oestrogen concentrations

fat cells in breast tissue produce oestrogen causing breast cancer

more oestrogen & attraction of white blood cells increases tumour size