control of gene expression Flashcards
substitution
one or more bases swapped for another
deletion
one or more bases removed
addition
one or more bases added
duplication
one or more bases repeated
inversion
a sequence of bases is reversed
translocation
sequence of bases moved from one location in genome to another
(could be within same or different chromosomes)
when do gene mutations occur?
spontaneously during DNA replication
mutagenic agents increase the rate of mutation
effects of mutations
different amino acid sequence made in polypeptide
change in sequence may change tertiary structure of protein
could stop it functioning
eg if its an enzyme, active site won’t be complementary shape to substrate
what does degenerate mean? and its impact on mutations
some amino acids coded for by more than one DNA triplet
means not all mutations change amino acid sequence
what is a frame shift?
happens due to mutations
- often addition, duplication and deletions
happens as they change the number of bases in a DNA code
changes nature of all base triplets that follow, code read in a different way
- affects amino acid sequence
examples of mutagenic agents
UV radiation
ionising radiation
chemicals
how can mutagenic agents increase rate or mutations? (3)
act as a base
- substitute for a base
- causes substitution mutations
- changes base sequence
alter a base
- can delete or alter bases
- changes sequence
changing DNA structure
- causes issues in replication
- increases likelihood of mutations
causes of cancer
when mutations happen in genes that control cell division
- tumour supressor genes
- proto-oncogenes
causes uncontrolled cell growth
results in tumour
- mass of abnormal cells which invade and destroy surrounding tissue
malignant tumours
cancers
- grow rapidly
- invade and destroy surrounding tissue
- cells can break off and spread in bloodstream
benign tumours
not cancerous
- grow slower
- covered in fibrous tissues, stops invading
- often harmless, can become malignant
what do tumour cells look like?
- irregular shape
- larger and darker nucleus
- different antigens
- divide more frequently (don’t respond to regulating processes)
role of tumour suppressor genes
working normally:
- slow cell division
- produce proteins to stop cell division or to make cells self destruct
can be inactivated by a mutation:
- doesn’t produce protein to slow division
- stimulates cells divide uncontrollably = tumour
role of proto-oncogenes
working normally:
- stimulate cell division
- produces proteins to make cell divide
effect can be increased due to mutation:
- gene becomes overactive
- stimulates cells to divide uncontrollably = tumour
what are oncogenes?
Mutated proto oncogene
caused by hypomethylation
what is methylation?
adding a methyl group
methylation of DNA controls weather or not the DNA is transcribed and translated
abnormal methylation is when it happens to much or too little
- hypomethylation
- hypermethylation
how can abnormal methylation cause tumours?
- hypermethylation of tumour - suppressor genes
- gene isn’t transcribed
- protein to slow division not made
- divide uncontrollably = tumour
- hypomethlyation of proto-oncogenes
- act as oncogenes
- increases amount of proteins that stimulate cell division
- divide uncontrollably = tumour
how does oestrogen cause cancer?
increased exposure over long periods of time - increased risk of breast cancer
- can stimulate certain breast cells to divide
more cell division taking place increases chance of mutations and cells becoming cancerous - the ability to stimulate division mean any cancerous cells would be able to divide even faster
tumour form more quickly - may be able to introduce mutations directly in DNA causing mutations
2 types of risk factors
something that increases someones chance of developing cancer
genetic - linked to specific inherited alleles - if inherited, more at risk
environmental - exposure to radiation, smoking, increased alcohol and fat diet increase risk