MolBio11 - 26 Flashcards
What are isoforms?
The different forms of protein that can be made from a single gene
How are isoforms created?
Alternate splice sites, start sites, poly-A sites
Where are isoforms most important for humans?
Immune system - generation of a/b from very small number of genes
Where is the most dramatic array of isoforms?
Neural - 38,000
What is the best characterised form of the regulation of alternative splicing?
Sex determination in drosophila - female have two Xs, males have one
What three genes regulate male and female differentiation in drosophila?
Sex lethal (sxl), transformer (tra), doublesex (dsx)
What is different in male drosophila splicing than in female?
sxl and tra are spliced to give rise to inactive proteins, resulting in a large dsx splice
What do dsx transcripts give rise to?
Either female or male repressive proteins, dependent on splicing
Outline the female drosophila sxl/tra/dsx pathway
Splice site in sxl blocked = functional sxl, sxl upregulates itself and blocks tra = functional tra, tra increases dsx splice length = repressor of male differentiation genes
Where does sxl bind?
U2AF
Which cell type exhibits polyA splice site isoforms?
B lymphocytes
What are the two B lymphocytic splices?
Long transcript = first stop spliced out = translation of a transmembrane domain; short transcript = splice lost = stop not lost = antibody secretion
What is the optimual start sequence?
Kozak sequence - accAUGg
How are alternative start sites identified?
Leaky scanning - small ribosome scans past first and stops and second or third
What favours the first AUG in a cell?
High levels of eIF-4F
What are the steps of HIV infection?
Integration of genome into host, transcription of entire genome, alternate splicing leads to many different protein products
What is Rev’s role in HIV?
Binds to unspliced RNA to allow the exit from the nuclear pore
Why can’t new HIV virions leave the nucleus?
They are unspliced, and so are restricted by the nuclear pores
What is a UTR?
Untranslated region
Why are UTRs important?
Can target mRNAs to parts of the cell
How do UTRs target mRNA to parts of the cell?
Intermolecular base pairing within the 3’ UTR forms recognisable stem loops
Where are translational control elements normally?
UTRs at either end of mRNAs
What is ferretin’s role?
Mops up Fe
What is transferrin’s role?
Imports Fe into the cell
What happens in low Fe concentrations?
Aconitase binds and blocks ferrin translation, but binds and facilitates transferrin production
What happens in high Fe concentrations?
Aconitase unbinds an facilitates ferrin translation, but unbinds and allows transferrin to be degraded
