Gene expression Flashcards
Gene expression
DNA template (codes for all proteins that can be made) - then to mRNA - then into protein.
How many genes in a human?
Approx 21,000
What is the mechanism that changes a gene into mRNA?
Transcription
What is the mechanism that changes mRNA into Proteins?
Translation
How many mRNA molecules in human?
Approx 196,000
How many proteins in a human?
> 300,000
What are the modifications that take place after proteins are made?
Post-translational modifications
Does translation and transcription take a lot of effort?
Adding a functional process to every human gene in genome a huge percentage of genes involved in translation and transcription.
Why do cells look different in different areas?
Even though all cells contain same DNA, gene expression is very tightly controlled. Only certain genes expressed in certain proteins.
Where is the DNA found in the cell?
In the nucleus
Where does transcription take place in the cell?
In the nucleus
Where does translation take place in the cell?
In the cytoplasm - More specifically in the RER but ribosomes.
Histones
DNA wrapped around these large protein molecules.
What is the structure of a DNA molecule
Double helix. Base pairs in the middle. Sugar and phosphate group runs on ladder.
What are the 4 base pairs?
Guanine
Adenine
Cytosine
Thymine
A-T
G-C
What is a codon?
Three base pairs in a row. This is a signal for adding a specific amino acid during protein expression.
What is a poly A tail?
A base repeated at end potentially defines how stable mRNA is, how long will be there.
Chromatin
Tiny space so when combined with histones and proteins. Helps decide wether gene will be transcribed or not.
Euchromatin
Open structure of chromatin - more likely to be transcribed. DNase1 sensitive, hyperacetylated, phosphorylated and not methylated allowing transcription to proceed.
Heterochromatin
Closed structure of chromatin - less likely to allow transcription.
RNA Polymerase
Large protein structure that is made to then go back into nucleus and transcribe DNA.
Polymerase 2 most common.
Huntington’s disease gene
One of the largest genes. 169408 bases, 67 exons.
How do we know when a gene has started or ended?
Promoter shows when it has started. STOP codon or poly A tail shows the end.
Does the whole gene get made in to mRNA?
No. It does not transcribe the promoter. There will be a start codon 5’UTR and a STOP codon 3’UTR
Do introns and exons both get transcribed into mRNA?
Yes but Introns do not stay. There is exon splicing in the nucleus. This mature mRNA with be transported from nucleus to cytoplasm.
How does transcription start?
Specific Protein will bind to promoter at the right time. ‘Make more protein’.
TF.. and TBP
Come to recognise promoter together.
What does the promoter site on a gene look like?
Can be Distal promoter region.
Proximal promoter region (-200 to -50 bp before, CCAAT Box at -75bp).
Core promoter region (BRE and TATA Box at -25bp)
There will be a TF complex.
INR then transcription.
Are sequences in promoter for all genes in general?
No. All promoters have general (ubiquitous) transcription factors as well as tissue-specific to precisely control gene expression.
How many transcription factors are there?
100’s. Grouped together by structure.
Are there any other elements that can affect transcription rather than just the promoter site?
Yes.
Enhancers - Positively Regulate transcription - can be a long way away - hard to find.
Silencers - Negatively regulate transcription.
Boundary elements - Block spreading of influence of agents such as enhancers or silencers.
Response elements - Sensitive to specific external stimuli such as glucocorticoids.
Why is splicing important? How is it related to the small number of bases available?
Can use the same gene in many different ways and to create many different proteins.
How do you find out which part of a gene expresses for certain things?
Compare the gene to the mature mRNA. As anything missing would be the intron. Only exons are left, meaning that this part is what expresses what you are looking at.
What is at the beginning and end of an intron?
GT at beginning. AG at the end. always. Around these slightly varies.
What is the implication of splicing where there is not AG?
It would not know to stop transcribing.
What happens in translation?
In ER. Complimentary t(transfer)RNA with one end as an amino acid and other end as an anti codon. These match to the codons on mRNA and determine order of amino acids = protein.
Redundancy RNA
All amino acids are given a single letter code to show what the codon encodes for. Some amino acids can be made through multiple codons.
What is different when DNA is being encoded into RNA ?
It puts a U instead of a T
What is the START codon for translation?
ATG (Methionine)
What is the STOP codon?
TAA, TAG, TGA
Post translational modification
Bonds between amino acids.
Phosphorylation - switching protein on or off.
Modified in ER by enzymes.
Removal of signal peptide, addition of carbohydrates, folding, disulfide bonds formation. Only properly modified proteins transported from ER to final destination.
