3.8.2.2 Regulation of transcription and translation (C20) Flashcards
Molecules which regulate the expression of genes are called..
transcription factors
Where do transcription factors bind to regulate gene expression?
(upstream of the gene) Promoter region
What do transcription factors do to regulate gene expression?
encourage binding of RNA polymerase (turn on genes) or prevent RNA polymerase binding (turn off genes)
When a cell receives a signal to express a gene what does the transcription factor do?
moves from the cytoplasm to the nucleus
Can specialised cells change into other cell types?
Housekeeping genes e.g. genes involved in respiration
Name a hormone that can regulate transcription
oestrogen
What type of hormone is oestrogen?
steroid hormone
How can oestrogen enter the cell?
lipid soluble and diffused through the phospholipid bilayer
Transcription is when
DNA is copied into mRNA
Translation is when
mRNA is translated into a sequence of amino acids
What does oestrogen bind to to regulate transcription?
Complementary receptor site on the transcription factor
When oestrogen binds to the receptor on the transcription factor what happens?
The DNA binding site changes shape on the transcription factor is now able to bind to DNA (transcription activated)
Why is oestrogen able to bind the receptor on transcrption factor?
oestrogen has a complementary shape the the receptor
What property of oestrogen allows it to diffuse through the phospholipid bilayer?
lipid soluble
Who proposed the structure of DNA?
Watson and Crick
What is meant by epigenetics?
heritable changes in gene function without change the base sequence of DNA
What sort of environmental factors might influence phenotype?
stress, sunlight, chemical exposure, diet,
How is your DNA organised into chromosomes?
DNA wrapped around proteins called histones (forming chromatin)
DNA and histones are covered in chemicals known as ..
tags
Give examples of DNA tags
Methylation
Acetylation
(Phosphorylation)
Tags attached to the DNA and histones form a second layer known as..
the epigenome
What determines the shape of the DNA and histone complex?
epigenome
DNA that is tightly packed, preventing transcription factors binding leads to
gene silencing
DNA that is loosely packed, allowing transcription factors to access the DNA leads to…
gene activation/expression
DNA code is fixed but your epigenome is…
flexible
What does your epigenome respond to?
the environment
Tags attached to DNA are knowns as
methylation
acetylation
When the association of DNA and histones is weak what does this mean for gene expression?
transcription factors can access the DNA and turn ON a gene
Tight association of DNA and histones affects gene expression - how?
prevents transcription factors binding to the DNA so turns OFF gene expression
tight association of DNA and histones is brought about by..
decreased acteylation and increased methylation
loose association of DNA and histones is brought about by..
increased acteylation and decreased methylation
What does decreased acetylation do to the histone proteins?
increased + charge so more strongly attracted to phosphate in DNA
Why does methylation prevent transcription?
- prevents transcription factors binding to DNA
- attracts proteins that would condense DNA
increased gene expression is brought about by
more acetylation and less methylation
reduced gene expression is brought about by
less acetylation and more methylation
acetyl group binds to
histones
methyl group binds to
DNA
more acetylation causes…
increased gene expression/DNA loosely packed
MORE methylation causes…
reduced gene expression/DNA tightly packed
LESS acetylation causes
reduced gene expression/DNA tightly packed
LESS methylation causes
increased gene expression/DNA loosely packed
epigenetics has been associated with what type of disease
cancer
do epigenetic changes alter the DNA base sequence?
NO
Preventing gene expression can also be done at the level of mRNA - how?
mRNA is cut up to prevent it being translated
what type of molecule is involved in silencing mRNA?
siRNA
Once siRNA is formed what does it associate with?
an enzyme
What is unique about the siRNA and the mRNA it is going to silence?
Their base sequences are complementary
enzymes can remove acetyl groups - how would this affect transcription?
less acetylation - reduced gene expression (mRNA not transcribed)
enzymes can remove acetyl groups - how would this affect DNA-histone complex?
tightly packed
How do transcription factors move?
from the cytoplasm to the nucleus
Expression of genes can be affected by other molecules e.g. hormones e.g. ….
oestrogen
can epigenetic changes be inherited?
yes!
