Control of Gene Expression - Transcription and Cancer Flashcards
what stimulates DNA to start transcription?
transcription factors
which genes will transcriptional factors stimulate transcription for?
genes switched on only
what can activate transcription factors?
oestrogen
how does oestrogen activate transcriptional factors?
diffuses through cell membrane and binds with complementary transcriptional factor in cytoplasm
transcriptional factor changes shape
enters nucleus through a pore
binds with DNA at specific base sequence - stimulates transcription
how do transcriptional factors stimulate the transcription of genes?
by binding to a specific base sequence in DNA
why can’t transcriptional factors bind to genes that are switched off?
the site on the DNA that binds to the transcriptional factors are not active
what determines whether a gene is switched on or off?
association of histones
chromatin
how does the association of histones affect whether a gene is turned on or off?
histones affect how tightly the DNA can wind around itself, so determining if the genes are accessible or inaccessible
when the association of histones is weak - is the gene switched on or off and why?
the DNA is loosely packed so it is accessible to transcriptional factors and the gene is switched on
when the association of histones with DNA is strong - is the gene switched on or off and why?
DNA tightly packed around the histones so is inaccessible to transcriptional factors
gene is switched off
what affects the association of histones with DNA?
acetylation of histones
methylation of DNA
how does acetylation of histones affect their association with DNA?
it affects the overall charge of the histone - which then affects how associated it is with the DNA sequence
what happens when acetyl groups are added to histones?
the histones are less associated with DNA
explain how adding acetyl groups to histones can switch on a gene
acetyl group added to histone
histone association with DNA decreases
DNA becomes less tightly wrapped
genes become accessible to transcriptional factors
gene switched on
what happens when acetyl groups are removed from histones?
the association of histones with DNA increases
explain how deacetylation leads to genes being switched off
acetyl group removed from histone
histone association with DNA increases
DNA becomes more tightly wrapped
genes inaccessible to transcriptional factors
gene switched off
what are the ways that methylation can affect whether genes are switched on or off?
affecting binding of transcriptional factors
affects rates of deacetylation of histones
during methylation, where is the methyl group added?
to a cytosine base of DNA
how does methylation affect the binding of transcriptional factors?
increased methylation prevents binding of transcriptional factors
how does methylation affect levels of acetylation of histones?
increased methylation induces deacetylation by attracting histones
explain how increased methylation can switch off a gene
increased methylation
deacetylation induced
increased association between DNA and histones
DNA more tightly wrapped
genes innaccesible to transcriptional factors
gene switched off
explain how decreased methylation can turn on a gene
decreased methylation
increased acetylation
association between DNA and histone decreases
DNA wrapped less tightly
gene more accessible to transcriptional factors
gene switched on
how does chromatin affect whether genes are switched on or off?
different forms of chromatin can affect how tightly wound DNA is
what are the types of chromatin that effect whether genes are switched on or off?
heterochromatin
euchromatin
what effect does heterochromatin have on DNA?
winds DNA in tightly
what effect does euchromatin have on DNA?
packs DNA looser
what is the difference between heterochromatin and euchromatin?
heterochromatin is a dense form of chromatin
euchromatin lightly packed form
what is epigenetics?
where environmental factors cause heritable changes without changing the order of the DNA code
what is the epigenome?
the tags on DNA wound around histones
what does the epigenome determine?
the shape of DNA
what is significant about the epigenome determining the shape of DNA?
the shape keeps inactive genes silenced
what is epigenetic silencing?
the epigenome keeping inactive genes silenced
what is the epigenome’s cellular memory?
the epigenome remembers signals it has received throughout its lifetime
what is an example of the epigenome being flexible?
tags can be changed by the environment
what environmental factors can affect the epigenome?
diet, stress
where does the epigenome receive signals from?
other cells in the body
when in the early foetal stage - from mother as well
how can epigenetic tags be removed?
by radiation
what happens if mRNA is destroyed before translation?
protein synthesis cannot occur
what can cause mRNA to be destroyed before translation?
siRNA
what is siRNA?
small interfering RNA
molecule that stops the translation of mRNA
why is siRNA useful?
prevents synthesis of proteins from genes that can cause diseases
how is siRNA made?
an enzyme cuts dsRNA into siRNA
how does siRNA prevent mRNA from being translated?
siRNA binds with the enzyme used to cut dsRNA into siRNA
siRNA and enzyme bind with complementary bases on mRNA
enzyme cuts mRNA into sections
mRNA can no longer be translated
what is dsRNA?
double stranded RNA
(synthesized by humans)
what genetic factor causes cancer?
damage to genes that regulate mitosis and cell cycle
compare the growth rates of benign and malignant tumours
benign - slow
malignant - quick
what is the appearance of nuclei in benign tumours?
normal
what is the appearance of nuclei in malignant tumours?
larger and darker
holding more DNA to divide
what is the differentiation of cells in benign tumours?
same differentiation of cells as before the tumour grew
what is the differentiation of cells in malignant tumours?
de-differentiated cells
do benign tumours spread?
no - due to adhesion molecules keeping the tumour together
do malignant tumours spread?
yes as they have no adhesion molecules so spread through bloodstream
do benign tumours have a capsule around the tumour?
yes - surrounding the whole tumour
what do malignant tumours contain instead of a capuse?
finger-like projections
what are the treatments for benign tumours?
surgery
what are the treatments for malignant tumours?
chemotherapy, radiotherapy, surgery
what genes can cause cancer?
tumour suppressor genes
oncogenes
what is the role of a proto-oncogene?
to stimulate cell division when growth factors attach to a protein receptor, activating a gene that tells DNA to replicate
what happens when a proto-oncogene mutates into an oncogene?
oncogene is permanently activated so always stimulating cell to divide regardless of growth factors
receptor protein always activated
may also produce more growth factors
can oncogenes be inherited?
yes
what is the role of tumour supressor genes?
slow down cell division
repair DNA mistakes
tells cells when to die (apoptosis)
what happens to mutated tumour surpressor genes?
become inactivated
what is the effect on the cell of mutated tumour supressor genes?
most die
some clone to form tumours due to uncontrolled division
are tumour supressor genes inherited?
not normally, most acquired by mutation
how can hypermethylation lead to cancer?
hypermethylation occurs in specific region of tumour supressor gene
tumour surpressor gene inactivated
gene switched off
how can hypomethylation lead to cancer?
hypomethylation of oncogenes, oncogenes more activated
what is the role of oestrogen?
regulates menstrual cycle
why is it more common for women to develop breast cancer after menopause?
reduced production of oestrogen in ovaries
fat cells in breasts produce more to compensate
oestrogen can stimulate tumour growth as it is a transcriptional factor
