Lecture 8: CSF Cell Signalling Flashcards
(42 cards)
What are the two types of cell signalling?
Local signalling
Long distance signalling
What is local signalling?
Cell signalling where signals cat on nearby target cells
e.g. neurotransmitters such as acetylcholine
What is long distance signalling?
Signals that act from a distance - hormones produced by cells travel via circulatory system to act on specific cells
e.g. insulin from beta cells in pancreas
What are the 3 steps to cell signalling?
Reception
Transduction
Response
Explain the reception stage
Signalling protein (otherwise called primary messenger or ligand) binds to a receptor protein causing a change in shape of the receptor protein
Explain the transduction stage
The altered receptor protein activates another protein (eg G-protein). The activated protein may cause a relay of changes causing other proteins to be activated.
Each activated protein causes a series of changes - often via phosphorylation.
Explain the response stage
All activated proteins cause a certain function or functions to occur in the cell
What is a TARGET receptor?
It’s the receptor with the complementary shape to the shape of the ligand - structure determines function
Is the type of cell receptors specific to the type of the cell?
No, there may be different receptor molecules on the cell surface membrane of one cell type at different points in time
What are the two types of receptors?
Intracellular and membrane-bound/cell surface receptors
What are intracellular receptors?
Primary messenger is generally hydrophobic and small - lipid soluble.
What are membrane bound / cell surface receptors?
Primary messenger is generally hydrophilic and/or large
examples include GPCR (G protein coupled receptor) and ligand-gated ion channels
What are GPCRs?
G-protein coupled receptors are transmembrane proteins that pass through the membrane 7 times.
Its extracellular portion has ligand binding site and its inner portion has loops that interact with G proteins.
It is the target for 1/3 of all modern drugs
What are G proteins?
G proteins are molecular switches which are usually inactive when GDP is bound and then become switched on or active when bound to GTP (guanosine triphosphate)
How does the cell signalling process occur with G-protein coupled receptors?
- At rest, receptor is unbound and G protein is bound to GDP (inactive). The enzyme in the plasma membrane is in an inactive state.
- When the ligand binds to the receptor site of the protein, the receptor changes shape allowing G protein with GTP (hence active) to bind to the receptor molecule. The enzyme is still inactive at this stage.
- Activated G protein dissociates from receptor along with attached GTP. Enzyme is activated by the G protein to elicit a cellular response.
- G protein has GTPase activity (GTP is broken down into GDP and P) causing its release from the enzyme reverting back to resting state.
What are ligand gated ion channels?
A receptor protein containing a gate. Binding of ligands to the receptor causes change in shape opening the gate and allowing entry of ions.
What is a receptor?
A protein molecule which responds to a specific ligand
What is a ligand?
A messenger molecule which binds to a specific receptor
What is an ion channel?
A transmembrane protein through which specific ions can travel
What is an ion channel receptor?
A membrane protein through which specific ions can travel, in response to ligand binding
How does cell signalling process occur with ligand gated ion channels?
- At rest, the ligand is unbound and the gate is closed
- Upon ligand binding, the receptor molecule changes shape causing opening of gate allowing specific ions to enter cell.
- When ligand dissociates, ion channels close.
What is an internal body system that relies heavily on ligand gated ion channels?
Nervous system - the transmission of action potentials across synapses occur via neurotransmitters that bind to ligands and open ion channels.
What is protein kinase?
An enzyme that is able to transfer phosphate group from ATP to another protein - hence activates the subsequent protein in the transduction stage of cell signalling
What is a phosphrylation cascade?
A series of reactions in which inactive protein kinase molecules are activated via the transfer of phosphate groups from ATP to the protein kinase. Ultimately leads to the activation of a protein that will cause a cellular response.
