E8 Regulation of gene expression Flashcards
(37 cards)
how can a cell be changed in terms of protein and RNA?
- changing a cell requires changing the synthesis and / or decay of specific proteins
- depends on how much genes are expressed and how fast proteins are degraded
- input and output should be changed accordingly to how much you need RNA or protein
describe glucocorticoid receptors and how they enter the nucleus
- gene specific transcription factors that are released from the cytoplasm upon the glucocorticoid hormone binding
- undergo conformational change that allows them to enter nucleus and bind to genes
how does the glucocorticoid hormone change transcription of a cell without entering the cell?
- peptide hormone is hydrophilic, membrane is hydrophobic and cytosol is hydrophilic
- membrane is a tight barrier and it’s difficult for hormones to translocate into the cell
- instead hormone binds to receptor on outside of cell with transmits change to the inside of the nucleus
what processes mediate switching in signal transduction?
- phosphorylation and dephosphorylation
- relays of phosphorylating can be started
what is the function of a protein kinase?
- enzyme that adds a phosphate
- phosphorylating can switch signalling on
- makes proteins active
what is the function of a phosphatase?
- enzyme that removes a phosphate
- dephosphorylation can switch signalling off
- usually deactivates a protein
what does the signal transduction cascade do?
- amplifies signal and carries it into the cell
what is a receptor kinase? what happens when it is active and inactive?
- allosteric switch (embedded in membrane)
- inactive when no hormone / growth factor is bound
- when activated, intracellular kinase is activated by phosphorylation
what happens when intracellular kinase is activated by phosphorylation?
- process passes a signal through the cell membrane by activating an enzyme that will phosphorylate internal targets
what is a common feature of cancer in terms of receptor kinases?
over activation of receptor kinases
what could cancer drugs be in order to block or reduce receptor activation?
antagonist
- prevent activation of receptor
- could be similar to the ligand for the receptor
- could be complementary to active sit or compete with the ligand
kinase inhibitor
- molecule that prevents the enzymatic activity of the receptor or downstream kinases
- could be similar to ATP
state the 5 common mechanisms for the control of gene expression
- regulation of transcription
- splicing
- regulation of translation
- regulation of mRNA degradation
- regulation of protein degradation
describe regulation of transcription as a mechanism to control gene expression
- main control of gene expression
- regulates the amount of pre-mRNA synthesised
- transcription factors binding to DNA to cause transcription
describe splicing as a mechanism to control gene expression
- determines which parts of the pre-mRNA end up in the mRNA
- involves dividing and processing of pre-mRNA (keep exons, bin introns)
- certain sequences bring in proteins that will cut out sections of the RNA (introns)
describe regulation of translation as a mechanism to control gene expression
- determines how much protein is made from a particular mRNA and therefore the protein level
- depends on the sequence and the structure of the sequence
- depends on how well the mRNA is produced
describe regulation of mRNA degradation as a mechanism to control gene expression
- determines how fast mRNA is degraded and therefore the level of an mRNA
- some mRNA may degrade very fast as the protein may have very dramatic effects so you only want them for a short time
- depends on how well the mRNA is produced
- if mRNA is degraded slowly but made fast, lots of mRNA will build up and lots of protein will be made
describe regulation of protein degradation as a mechanism to control gene expression
- determines how fast a protein is degraded and therefore the protein level
- mechanisms in the cell can down-regulate receptors and flag proteins for degradation
what 2 categories do the 5 mechanisms of gene expression control fit into? state which mechanisms go where
nuclear recognition and cytoplasmic regulation
nuclear regulation
- regulation of transcription
- splicing
cytoplasmic regulation
- regulation of translation
- regulation of mRNA degradation
- regulation of protein degradation
describe splicing
- introns are removed from the pre-mRNA (introns can be very large)
- exons are expressed
- exons and introns can be considered as each other sometimes (alternative splicing. -different cells may splice the same piece of pre-mRNA into different mature mRNA)
how can exons be skipped in splicing and what can this allow for?
- exons can be skipped by disguising them as introns so they’re not expressed
- this can then cure diseases because a slightly different protein can be translated form the same pre-mRNA
how can splicing cure cancer?
- can splice around mutations and leave out mutated mRNA
what do mRNAs acquire as well as removal of introns?
- a cap structure at their 5’ end and a poly(A) tail at the 3’ end
describe capping
- cap structure at 5’
- protects the 5’ end
- accumulation of proteins
- cap allows for translation (poor without cap)
- interacts with polyA tail when mRNA loops round
describe polyadenylation
- poly(A) tail at 3’ end
- protein sticks lots of A’s onto the RNA to make mRNA
- length of polyA tail determines how efficiently the mRNA will be used for translation
