Cell Biology Theme 2

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  • Created by: Splodge97
  • Created on: 13-05-17 17:37
What is paracrine signalling?
When cytokines/growth factors released by specific cells diffuse through the extracellular matrix and bind to specific receptors on local target cells (activating intracellular pathways)
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What is autocrine signalling?
Where a cell secretes a horrmone/chemical mesennger which binds to autocrine receptors of the same cell (to activate inttracellular pathways) - some neighbouring cells of the same type may also be affected, amplifying the effect
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Give an example of contact dependant signalling
Delta/notch signalling - newly developed nerve cells have inhibitory delta proteins on their surface which bind to notch receptors on epithelial cells to inhibit their differentiation into neurones
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What are the possible actions of GPCR's once activated?
May activate PKA to phosphorylate an intracellular protein switch (stopped by release of Pi by the switch during ATP hydrolysis) or bind GTP to its intracellular site (stopped by loss of Pi in GTP hydrolysis); both affect signalling pathways
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What is the role of RNA polymerase in transripiton?
Once activated by binding of transription factor to comittee binds to promoter and forms single stranded pre-mRNA by linking ribonucleutide triphosphates with phosphodiester bonds (anti-parallel to template strand except T=U)
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What are contiguous genes?
Similar function so clustered together in operons
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How is splicing achieved?
Removal of sections on pre-mRNA coding for introns, placement of small 5' RNA cap at start and polyadenyl tail (many repeating adenine bases) at the end; these allow specific folding so it can fit through the nuclear pore
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What is alternative RNA splicing?
Where exons of pre-mRNA are re-ordered in the mRNA (so same gene can produce different proteins)
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What is the function of rRNA?
Influences ribosome structure, acts as a catalyst in translation
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How does miRNA act?
Destroys mRNA by cleaving it or shortening its poly-A tail
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How does siRNA act?
Binds to a dicer protein to split into small sections then associates with RNAases which cleave mRNA (when siRNA binds to it via its complementary bases)
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What is 'wobble'?
Ability for tRNA to bind to different codons as long as the first two bases are the same
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What are ribosomes comprised of?
Four rRNA strands and 80+ proteins (make up large and small sub-unit)
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What is the role of translational initiation factors?
Molecules which bind to the ends of mRNA to signal the start of translation (as allow small subunit and methionine tRNA to form a complex). Unbind when tRNA binds to start codon, allowing large sub-unit to bind and catalyse peptide bond formation.
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What is the role of the small sub-unit in translation?
Matches tRNA molecules to their specific mRNA codon
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Where does methylation occur in histones?
To lysine and arginine amino acids at the positive N-terminus
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What is the effect of glycosylation on proteins?
Glycoproteins formed are more stable, also promotes protein folding
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What are chaperone proteins?
Bind to nascent (primary) polypeptides to guide protein folding
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What is the purpose of an ER rretention signal?
Signal causing lipids/proteins to remain within the ER after maturation
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What are housekeeping genes?
Genes common in most cells of a species and most frequently transcribed (as they produce proteins which play major roles in most cells)
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Where are promoters located?
Upstream of a gene
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What are TATA-box sequences?
Sequences in the promoter where the transcription factor TFIID binds (so RNA polymerase starts transcription)
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What is the transcription initiation complex?
The complex which RNA polymerase is able to bind to once all transcription factors have bound to the promoter/comittee (once TFIID has bound to TATA-box etc.)
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What is constitutive transcription?
Standby transcription where RNA polymerase II has been phosphorylated whilst bound to the transcription initiation complex
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What are regulatory transcription factors?
These occur in eukaryotes; they aren't necessary for constitutive transcription but are necessecary for the gene to actually be transcribed. They also act to loosen heterochromatin and stimulate the binding of histone-modifying enzymes.
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What are activator proteins?
Regulatory transcription factors which bind to enhancers (upstream of promoters) to activate or repress formation of the transcription initiation complex
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What are leucine zippers?
Transcription factors which bind to promoter regions comprised of two leucine alpha helices
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What are zinc fingers?
Small transcription factors which are complementary to many promoter sequences (that have similar base sequences) - this allows them to control the expression of multiple genes
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What abilities do transcription factors with HDAC posess?
If they have histone deactylase activity they can remove actely groups from histones, repressing transcription. Associated with cancer as may inactivate tumour supressors.
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What is cell memory?
When, after initial activation by a transcription factor, a protein acts as its own transcription factor so it is continually produced (allowing cell differentiation)
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What are cortisol responsive genes?
Genes whiich have their transcription factors initiated by binding of cortisol
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What is MyoD?
A transcription factor which binds to its promoter sequence in fibroblasts to cause them to differentiate into muscle cells
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What are master regulatory genes?
Genes which encode transcription factors - in this case myogenic regulatory factors involved in the development of muscle cells
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What are homeotic genes?
Genes which encode transcription factors that supply positional information to cells (determine which cell types are expressed where); they may activate cascades of other transcription factors or initiate feedback loops
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What are Hox genes?
Genes which encode transcription factors - these transcription factors are then involved in embryonic development
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How can post-transcriptional control be important in development?
Through the action of siRNA or miRNA degrading mRNA and thus preventing proteins being expressed
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What are the hedgehog gene family?
Signalling molecules coded for by homeotic genes; as such they play roles in positional cell differentiation
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What role does the Ihh hedgehog gene play?
Mediates endodermal development
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What role does the Dhh hedgehog gene play?
Mediates neuronal development
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What role does the Shh hedgehog gene play?
Mediates embryonic development; a mutation is likely to cause cancer (so Shh pathway inhibitors are used as anti-cancer drugs)
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How is prokaryotic transcription different to eukaryotic transcription?
Prokaryotic transcription occurs in cell cytoplasm, occurs simultaneously with translation (has mRNA transcribed directly from template strand as no introns, so no splicing necessary), only one RNA polymerase type, DNA not associated with histones
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Card 2

Front

What is autocrine signalling?

Back

Where a cell secretes a horrmone/chemical mesennger which binds to autocrine receptors of the same cell (to activate inttracellular pathways) - some neighbouring cells of the same type may also be affected, amplifying the effect

Card 3

Front

Give an example of contact dependant signalling

Back

Preview of the front of card 3

Card 4

Front

What are the possible actions of GPCR's once activated?

Back

Preview of the front of card 4

Card 5

Front

What is the role of RNA polymerase in transripiton?

Back

Preview of the front of card 5
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