Cell Signalling Flashcards
What are 4 reasons we need cell signalling?
To process information
When an outpost is required from an input it is important the the body can communicate to do this
For self preservation
Eg fight or flight
Voluntary movement
Involves a lot of different sensory and motor organs all coordinated by the brain
For homeostasis
Eg blood glucose or calcium levels
Which two systems in the body provide lines of communication?
Nerve fibres in the CNS and PNS
The blood vessels of the CVS
What is the difference between communication using nerves and the blood
Nerves
Faster
But simple information
Blood
Slower
But other substances can be transported
What is the first step in neurotransmission (across a synapse)?
Propagation of the action potential
Voltage gates sodium channels open
Na+ influx —> membrane depolarisation —> propagation of action potentials
VGKC opens —> K+ efflux —> repolarisation
What is the second step in neurotransmission (across a synapse)?
Neurotransmitter released from vesicles
Action potential opens voltage gates calcium channels at presynaptic Terminal
Ca2+ influx —> binds to vesicles —> neurotransmitter released into synaptic cleft (exocytosis)
What is the third step in neurotransmission (across a synapse)?
Activation of postaynaptic receptors
Neurotransmitters bind to receptors on post synaptic membrane
Modulates post synaptic activity
What is the fourth step in neurotransmission (across a synapse)?
Activation of post synaptic receptors
These can come in a variety of forms
What is the method of transfer of information in the blood?
Hormones
Released from glands such as the pituitary and the hypothalamus
What is endocrine signalling?
Hormones travel within the blood vessels to act on a distant target cell
Give an example of Endocrine communication
Hypoglycaemia
Glucagon secreted by a-cells in the islets of langerhans in the pancreas
Glucagon travels in the blood to liver
In the liver it stimulates glycogenolysis and gluconeogenesis increasing blood glucose levels
What is paracrine communication?
Hormones acting on adjacent cells
What is an example of paracrine communication?
Hyperglycaemia
Increased blood glucose
Insulin secretion by B-cells of pancreas
Paracrine effects are inhibiting glucagon secretion in adjacent a-cells
(Also has endocrine effects in the liver)
What is cell signalling between membrane attached proteins?
Plasma membrane proteins on adjacent cells interacting
What is an example of signalling between membrane attached proteins?
Immune reaponse
Blood borne virus (eg hep C ) enter blood
This is detected by an antigen presenting cell
APC digests pathogen and expresses major histo-compatability (MHC) class II molecules on surface
Circulating T lymphocyte engages with MHC molecule through T-cell receptor (TCR) interaction
What is autocrine signalling?
Signalling molecule acts in the same cell
What is an example of autocrine signalling?
Activated TCR initiates a cascade of reactions within the T cell
Activated T cell expresses interleukin-2 receptor on surface
Activated T cell also secretes IL-2
This binds to IL-2 receptor in same cell, as well as adjacent cells
What are the four categories of receptors?
Ligand gated ion channel receptors (ionotropic receptors)
G protein coupled receptors
Enzyme linked receptors
Intracellular receptors
What are some properties of ligand gated ion channel receptors?
Central pore incorporated into their quaternary structure
When the appropriate ligand attaches to the ‘ligand binding domain’ the pide opens
Eg nicotinic acetylcholine receptor binds acetylcholine ligand. This effects muscle contraction or cognitive enhancement
(Look at insendi for examples)
How do ligand gated ion channels work?
Ligand binds to receptor protein
Change in confirmation of channel protein opens pore
Pore allows ions to move through depending on the direction of the concentration gradient
What are G protein couples receptors?
Aka 7-transmembrane receptors
Linked to an intracellular G protein complex, consists of an alpha subunit, a beta-gamma subunit and an associated GDP molecule
How do G protein coupled receptors work?
7-TM receptor and heterotrimeric G protein are inactive and un bound p
Ligand binds, conformation of receptor changes
G protein trimer and associated GDP bind to receptor
GDP is phosphorylated to GT
G protein dissociates into the alpha subunit (with GTP) and the By subunit. These big d to their target proteins and induce the desired effects
To inactivate:
Ligand unbinds
GTPase dephosphorylates GTP to GDP
Alpha subunit dissociates from target protein
Trimmer forms again
What are enzyme linked receptors?
Only one transmembrane domain
This has a ligand binding domain on the outside and specialised enzymes (usually tiresome kinases) on the inside
They don’t usually work alone, require clustering of more than one receptor protein to activate enzyme
How do enzyme linked receptors work?
Ligand binds, causes receptors to cluster together
Clustering activates anzyme activity in the cytoplasm
the enzymes phosphorylation the receptor
Phosphorylation leads to the binding of signalling proteins to cytoplasmic domain
Signalling proteins generate a cascade of effects within the cell
What are intracellular receptors?
Steroid hormones are mambrane permeable (hydrophobic, lipophilic)
Therefore need intracellular receptors
These are essentially transcription factors, so regulate mRNA and protein synthesis
Two types. Type I, type II
How do type I intracellular receptors work?
Cytoplasmic - located working the cytosolic compartment
Associated with chaperone molecules (heat shock proteins)
Hormone binds to receptor, causing hsp to dissociate
2 hormone bound receptors form a homodimer
This translocates to the nucleus, and binds to DNA
How do type II intracellular receptors work?
Nuclear
Often already bound to DNA
Ligand binds to receptor in the nucleus
Leads to transcriptional regulation
