W2 - Cell to Cell Signalling Flashcards
What is trans autophosphorylation?
The molecule phosphorylates itself and then passes that phosphate on
What happens once a GPCR is activated?
GTP replaces GDP bound to alpha subunit, alpa/beta/gamma heterotrimer dissociates and alpha dissociates from this
Where does the GTP alpha go after it dissociates and what does this do?
Goes to effector protein and activates a cascade to reach target
What are the two forms of direct signalling?
Gap junction signalling and juxtacrine signalling
What are the four indirect forms of signalling?
Autocrine, paracrine, endocrine and neuronal signalling
In what instance would membrane bound receptors be typically used?
When the signal is hydrophilic (except gases)
What happens after transduction if there’s no 2nd messenger or if it’s there but is inactive?
Not there - enzyme is activated to produce 2nd M, is there but inactive - changes conformation of enzyme/messenger to activate 2nd M
Ligand and receptor interactions can be fast and/slow, give examples of these?
Fast - altering protein function (act/deact), Slow - altering gene expression (takes longer due to transc/transl)
What determines what the head and tail is in a fruit fly?
The protein gradients formed by bicoid and nanos proteins
What type of signalling is involved in the formation of chicken limbs?
Paracrine
What does the ZPA do?
Sends out signals which instruct the developing limb bud on how to form along the posterior/anterior axis
What would give more reference points in terms of ‘decisions made’ by what/how much morphogen are present and why?
Having multiple morphogens can give many more combinations to instruct what to produce (e.g. neurons from SC)
How to test French Flag hypothesis
Have normal ZPA working and observe, cut ZPA from one embryo using eyelash and add to opposite side (to current ZPA) of another to alter gradients
Wolpert’s conclusion is…
A morphogen produces a signalling gradient and this gives identities at thresholds
What is on the X and Y axis of Wolpert’s graph?
X - distance from morphogen source, Y - conc of morphogen
What is the difference when writing bicoid mRNA or bicoid protein?
mRNA - lowercase and italics, protein - capital letter and upright
What is special about the specificity of serine + threonine kinases and why?
Either kinase can phosphorylate either aa because their side chains are similar
Why can kinases only phosphorylate serine/threonine/tyrosine?
It requires a polar hydroxyl group on side chain
Why does phosphorylation increase hydrophilicity in serine/threonine/tyrosine?
Adds -ve charge so makes side chain charged
What does phosphorylation of tyr/thr/ser do to the structure of protein, allowing it to alter activity of another protein?
Conformational change
What enzymes are required for dephosphorylation?
Phosphatase enzymes
Are molecules always activated once phosphorylated?
No they can be inactivated too
What is the key steps of amplification?
One activated receptor activates many 2nd messengers, the 2nd messengers activate multiple kinases until they’re removed from cytosol/metabolised, each kinase can activate multiple targets
Amplification can be big or small, is it ever not there?
No
How do ligand-dependent transcription factors modulate gene expression?
Causing addition or removal of acetyl groups from histones
Where is the nicotinic acetylcholine receptor found?
Neuromuscular junction
How many subunits is the NAChR made up of and what happens when the biogenic amine ACh binds?
5, conformational change to open aqueous ion channel for movement of K+, Na+ and Ca2+
What terminal of transmembrane domains is the ligand binding domain in ionotropic receptors?
N-terminal
How many transmembrane alpha-helices in a GPCR?
7 (always)
What two parts of a GPCR makes up site of interaction for G-proteins?
3rd intracellular loop and C-terminal
What two things can G-proteins interact with once the GPCR is stimulated?
Ion channels or enzymes
GCPRs can couple many different G-proteins including heterotrimeric Gi/s/q/t/(12/13), what are the three subunits of these?
Alpha, beta and gamma
When GPCR is bound to, a conformational change occurs, what does this cause to happen?
Alpha subunit swaps GDP for GTP
What does the active GTP-bound alpha subunit do?
Dissociates from beta/gamma and moves along inner surface of membrane until it interacts with an effector protein
What in the GPCR signalling pathway generates the active second messenger ion/molecule?
The effector protein
What 3 things can stop the GPCR pathway?
GTPase activity (GDP relaces GTP to inactivate alpha), primary messenger not present or receptor is desensitised to ligand
What does Gs and Gi do to adenylyl cyclase? (ATP –> cAMP)
Gs - increases rate of activity, Gi - decreases rate of activity
How to turn cAMP into 5’-AMP? (stops activating PKA)
Cyclic nucleotide phosphodiesterase
Gq acts with phospholipase C, what does this enzyme do?
Hydrolyses PIP2 to form 2 secondary messenger molecules, DAG and IP3
IP3 acts on IP3 intracellular receptors to allow Ca2+ out of ER, what can Ca2+ then act as a 2nd messenger to?
CaM kinase, PKC
PKC can act on the AP-1 transcription factor, what is this TF used in?
Cell proliferation
How can the Gq signal pathway be stopped? (2 ways)
Hydrolysis of IP3 and moving Ca2+ out of intracellular space
In the receptor tyrosine kinases for insulin/IGF, what are the two parts of the receptor dimer joined by?
Disulphide bonds between cysteine R groups
Once the RTK is bound to, a conformational change occurs which allows for…
Phosphorylation of downstream signalling target proteins (e.g. IRS) and transautophosphorylation
Phosphorylated IRS can activate PI3K, what is the substrate for PI3K?
Membrane phospholipids
What type of receptor activity takes place for BMPs and transforming growth factors (beta)?
Receptor serine/threonine kinase (RSTK)
What proteins do RSTKs phosphorylate and what do the phospho form do?
Smad proteins, phospho smads act as TFs and regulate gene expression in nucleus
What non-receptor protein kinase enzymes do type I and II cytokine receptors associate with?
JAK enzymes
On binding the cytokine receptor, dimerisation occurs and then what?
JAK enzymes transphosphorylate tyrosine residues in the receptors
Through SH2 domains, what do the phosphotyrosines allow to dock onto the receptors? And then what happens?
STAT proteins, JAK enzymes phosphorylate the STAT proteins which causes them to dissociate and dimerise with each other
What do STAT-STAT dimers act as?
They act as TFs once transported into the nucleus
What do the enzyme linked receptors for ANPs include instead of kinases?
Guanylyl cyclase
What happens once the ANP binds to it’s receptor N domain? (vasodilation pathway)
Guanylyl cyclase is activated, GTP is made into cGMP and cGMP acts on PKG (ser/thre) to relax smooth muscle in blood vessels
What enzyme stops the ANP pathway and how?
cGMP-PDE, forms 5’-GMP so it can no longer activate PKG
What is an example of paracrine signalling?
Mast cells and immune cell recruitment for inflammation
