Unit 7- Transcription Factors and splicing Flashcards
What is a transcription factor?
Proteins that bind to DNA to regulate gene expression by enabling the binding of RNA polymerase
What ways are there to alter the structure of chromatin?
DNA methylation
histone modification
What are epigenetic changes?
Chemical changes to our DNA and histones as a result of environmental factors
What is chromatin remodelling?
Switching from loosely packed chromatin (euchromatin) to tightly packed chromatin (heterochromatin) as a result of DNA methylation and histone acetylation
Why can’t genes be expressed if the nucleosomes are tightly packed (heterochromatin).
Transcription factors can’t access and bind to the DNA
What is dna methylation?
- when a cytosine adjacent a guanine is methylated (CH3 group added) by the enzyme DNMT (DNA methyl transferase)
What happens when a cytosine in a gene is methylated?
- the region of DNA coils tightly to form heterochromatin
- transcription factors can’t bind
- gene expression is turned off
What happens when a histone is modified?
When the amino acid tails of histone proteins with DNA molecules wrapped around then (nucleosomes) are altered by addition or removal of groups
This can result in the DNA being more or less accessible to transcription factors
What is a nucleosomes?
A histone protein with DNA wrapped twice around it
What are histones?
Proteins that act as support fro DNA molecules in chromatin
What do transcription factors do? And how do they work simply
Bind to DNA in the nucleus to change the rate at which mRNA is produced
They make it easier or harder for RNA polymerase to bind to the DNA and begin synthesising pre mRNA
What 2 types of transcription factors are there?
- transcription factors
- activator proteins
How do transcription factors increase rate at which mRNA is produced?
They bind at the promoter sequence on DNA which makes the binding of RNA polymerase more easy
How do activator proteins speed up mRNA production.
They bind the an enhanced sequence of the gene (a region that isn’t the promoter sequence) which causes the DNA to loop and loosen its grip on the histone becoming more accessible for RNA polymerase to bind and begin transcription
Give 3 examples of transcription factor control:
- embryo development, embryos rely on TFs heavily to govern which genes are expressed to corm the correct tissues/organs
- hormonal control, cells affected by oestrogen have a receptor molecule which binds to form a complex, to activate specific genes (hormones are lipids that move into the cell by lipid diffusion bind to a receptor molecule in the cytoplasm and become a TF)
- control of cell cycle, changes in dividing cells and when a cell can device are controlled by TFs
- pathogens controlling host cells, some bacteria produce TFs which modify gene expression in host nuclei
What are spliceosomes?
Complexes made from proteins and RNA that carry out splicing
How can splicing of 1 gene result in many different proteins?
After introns and some Exons are cut out the remaining exons can be combined in different orders to make various isoforms of mature RNA
Give an example of how splicing can create 2 different proteins in humans
In humans the hormones CGRP and Calcitonin are made from the same gene
Calcitonin is made in the thyroid
CGRP is made in the hypothalamus
What is non-coding RNA involved in?
Controlling gene expression
siRNA (small interfering and micro) and miRNA both deactivate genes by RNA interference, how does this work?
These short strands of RNA bind to mRNA by complementary base pairing forming regions of double stranded RNA that cannot be translated in a ribosome so are broken down by enzymes, as a result inhibiting expression by causing the destruction of the gene in mRNA
What does noncoding RNA do?
Affects transcription and is important in inactivating genes and chromosomes
How can ncRNA affect chromosomes?
ncRNA can coat the X chromosome which super coils and condenses to form a stable Barr body the maintain the balance of gene products
How are epigenetic changes different to mutations?
Epigenetic changes do not alter DNA base sequences but mutations do
DNA maintains correct genetic information on how to produce a protein with epigenetic changes, whereas mutations change the genetic information
Epigenetic just change the degree to which genes are expressed
