BIOL124 - L2

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  • Created by: Katherine
  • Created on: 02-06-16 14:50
What are the three stages of cell signalling?
Reception, transduction and response
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What is reception?
Detection by the cell of a signal molecule that usually originates from outside the cell. The signal is detected when signalling molecule interacts directly with a receptor on cell surface or inside the cell. This is referred to as receptor binding.
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What is a ligand?
The signalling molecule - it is a small molecule that binds to a larger one.
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What can ligand binding lead to?
A change in the shape of a protein or aggregation of 2 or more receptors - enables receptros to interact with other molecules. Receptor activation can then lead to further molecular changes inside the cell.
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What are hydrophilic messengers?
Water soluble and often too alrge to pass through membranes are detected by membrane bound receptors
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What are hydrophobic messengers?
Can move through thel ipid environment of the PM and so signal receptors can be located inside the cell
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What are receptors in the plasma membrane like?
Most water soluble signal molecuels bind to specific sites on receptor proteins that span the plasms membrane.
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What are the 3 main types of membrane receptors?
G protein coupled receptors, Receptor tyrosine kinases, Ion channel receptors.
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What is a G coupled protein receptor?
The larges family of cell surface receptors. It is a plasma membrane receptor that span the membrane as sevven a helices.
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What to G coupled protein receptors require?
A G protein
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What is a G protein?
It is a molecular switch, either on or off.
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What can G proteins do?
They can bind guanine nucleotides - GTP (guanosine triphosphate) and GDP (guanosine diphosphate)
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When is a G protein active?
When GDP is bound to it. The switch is on.
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When is the G protein inactive?
When GTP is bount to the G-protein - the switch is off
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When does receptor activation occur?
When signalling molecule binds to extracellular side of GCPR
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What does activation mean?
It is change in shape of the receptor - cytoplasmic side of GCPR binds to the inactive G protein.
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What happens when there is interaction between G protein and GCPR?
GTP displaces GDP - G protein activation
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What does he activated G protein do?
It dissociates from GCPR - diffuses along membrane and binds to an enzyme. This causes change in shape and activity of enzyme - enzyme activation leads to a cellular response. Binding of signalling molecule is reversible.
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What determines how often signalling occurs?
Lignad concentration
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Why are changes in enzyme and G protein only temporary?
Because the G protein functions as a GTPase enzyme - it hydrolyses GTP to GDP
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What does this do
It returns G protein to inactive state and the G protein leaves the enzyme.
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What happens to the G protein then?
It's available for reuse - GTPase function allows the pathway to shutdown rapidly when the signalling molecule isn't present.
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Examples of signalling apthways that use G protein coupled receptors:
Epinephrine/adrenaline - from the adrenal gland - stiumulates glycogen breakdown in liver and skeletal muscle during stress.
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Signalling pathways that use G protein coupled receptors include:
Whooping cough, cholera, botulism.
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What are receptor tyrosine kinases?
They are membrane bound receptors which have intrinsic enzyme activity
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What do they act as?
As a tyrosine kinase - adds phosphaate residues onto other proteins.
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What can a RTK do?
It can trigger multiple signal transduction pathways at once.
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What is abnormal functioning of RTKs associated with?
Cancer
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Give an example of RTKs?
Animal growth factors - involved in cell growth and division.
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What is herceptin?
A monoclonal antibody that binds to receptors. When cancer causes excessive levels of RTKs called HER2, it binds to it and inhibits growth.
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What do ligand gated ion channels act as?
A gate - the structure creates a pore in the plasma membrane that can open or close in response to an extracellular chemical messenger.
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The gate is closed until...
A ligand binds to the receptor.
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What happens when a ligand binds to it?
Gate opens and specific ions can flow through the channel into the cell - this rapidly changes the intracellular concentration of that ion - causes cellular response. When ligand dissociated from the receptor the gate closes and ion can't enter.
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Are ligand gated on channel's important?
Yes, important in the nervous system e.g. neurotransmitter molecuels released at a synapse between 2 nerve cells. Neurotransmitter binds as ligands to ion channels of receivig cell. Causes channels to open
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What are some drugs which exert their effects through modulating ion channels?
Verapmil, Lamictal, Lidocaine, Glipizide
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Verapmil
Calcium channel blocker
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Lamictal
Sodium channel blocker
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Lidocaine
Sodium channel blocker
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Glipizidie
Potassium channel blocekr
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What are intracellular receptors?
They're found in the cytosol or nucleus of target cells
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What are they?
Small or hydrohpobic chemical messengers readily cross the membrane and activate receptors.
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An example of intraceullar receptors:
Steroid and thyroid hormones of animals
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Card 2

Front

What is reception?

Back

Detection by the cell of a signal molecule that usually originates from outside the cell. The signal is detected when signalling molecule interacts directly with a receptor on cell surface or inside the cell. This is referred to as receptor binding.

Card 3

Front

What is a ligand?

Back

Preview of the front of card 3

Card 4

Front

What can ligand binding lead to?

Back

Preview of the front of card 4

Card 5

Front

What are hydrophilic messengers?

Back

Preview of the front of card 5
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