cell signalling Flashcards
- What are the 4 reasons we need cell signalling?
To process information
Self-preservation Voluntary movement Homeostasis
- What direction does an action potential travel?
- How does an action potential travel?
From the pre-synaptic terminal to the post-synaptic cell
Na+ influx and K+ efflux Via Na+ and K+ transporters
- How are neurotransmitters released from vesicles?
- How does the activation of post-synaptic receptors occur?
AP opens voltage gated Ca2+ channels at presynaptic terminal
Ca2+ influx → neurotransmitter vesicle exocytosis into synaptic cleft
NT binds to receptors on post-synaptic membrane Receptors modulate post-synaptic activity
- What is meant by Endocrine Communication?
- Explain what occurs during Hypoglycaemia?
Hormones travel within blood vessels to act on a distant target cell
Glucagon secreted by alpha cells in the islets of Langerhans (in pancreas) Glucagon travels out of pancreas via blood vessels Glucagon stimulates glycogenolysis and gluconeogenesis within the liver → increasing blood glucose level
- What is meant by Paracrine Communication
- Explain what happens in Hyperglycaemia?
- What other examples?
Hormone acts on an adjacent cell
Increased blood glucose - insulin secretion by beta cells in the Islets of Langerhans Insulin has paracrine effects: Inhibiting glucagon secretion Insulin also has endocrine effects on the liver
Nitric oxide on endothelial cells in blood vessels
Osteoclast activating factors from adjacent osteoblasts
- What is cell signalling between membrane attached proteins?
- Example of cell signalling between membrane attached proteins? (think immune system)
- What are other examples?
plasma membrane proteins on adjacent cells interacting
Blood borne virus detected within blood stream by antigen presenting cell
APC digests pathogen and expresses major histo-compatibility (MHC) class II molecules on surface
Circulating T-Lymphocyte engages with MHC molecule through T-Cell receptor (TCR) interaction
HIV glycoprotein to CD4 receptors on T lymphocytes
Bacterial cell wall components to toll like receptors on haematopoietic cells
- What is meant by Autocrine Communication?
- Explain how Autocrine Communication works?
- What are other examples?
Signalling where molecule acts on the same cell
Activated TCR will initiate a cascade of reactions within the T-cell
Activated T-cell expresses interleukin-2 (IL-2) receptor on surface
Activated T-Lymphocyte also secretes IL-2, which
Binds to IL-2 receptor on same cell
Binds to IL-2 receptor on adjacent activated cell
growth factor eg TGF beta from tumour cells
AcH to presynaptic M2 muscarinic receptors
- What is a ligand?
- What is meant by a second messenger?
A chemical message or molecule that exerts its effects through binding to receptors
Chemical messenger that is a separate entity from receptor or ligand that evokes the intracellular effect
- How does the process of ligand-gated channel (ionotropic receptor) activation occur?
Ligand binds to receptor on channel protein
Change in conformation of the channel protein results in the opening of a pore which spans the cell membrane Pore allows ions to move in or out of the cell according to their respective concentration gradients
- What is a G protein complex consisting of?
Alpha subunit
Beta-gamma subunit Associated GDP molecule
- Explain the process involved in G protein complex activation
In resting state, G protein complex is in close proximity to the receptor
Ligand binding causes the G protein complex to associate with the receptor resulting in the GDP molecule being phosphorylated to a GTP molecule The G-alpha subunit dissociates from the G beta-gamma subunit Both G-alpha and G beta-gamma can act as secondary messengers When ligand dissociates from the receptor, internal GTPase on the G-alpha subunit hydrolyses GTP to GDP G-alpha and G beta-gamma subunits re-associate and are once again available to the receptor
- How does enzyme-linked receptor activation occur?
Ligand binding results in receptors clustering
Receptor clustering activates enzyme activity within the cytoplasmic domain Enzymes phosphorylate the receptor Phosphorylation leads to binding of signalling proteins to the cytoplasmic domain These signalling proteins recruit other signalling proteins to the cytoplasmic domain The signal is terminated when a phosphatase dephosphorylates the receptor
- Are steroid hormones membrane permeable?
- What is an intracellular receptor?
Yes, so they can exert their effect on intracellular membranes
A transcription factor, involved in regulation of mRNA and protein synthesis
- How do Type I intracellular receptors work?
- Explain how Type II intracellular receptors work?
Located within the cytosolic compartment and are associated with chaperone molecules
Once hormone binds to receptor, hsp dissociates so hormone-receptor complex forms a homodimer with another identical hormone-receptor complex
Homodimer translocates to nucleus where it binds to DNA and acts as a transcription factor
Located within nucleus of the cell and are often already bound to DNA
Binding of hormone ligand to the receptor usually results in direct transcriptional regulation by the activated hormone-receptor complex
what are examples of Ligand Gated ion channel receptors
Nicotinic Ach receptors- for Muscle contraction
GABA a receptor- inhibit neuronal activity
NMDA receptor- synaptic plasticity and memory formation
