Cell signaling Flashcards
Why do cells need to communicate?
- Process information:
- Sensory stimuli(e.g. sight,) - Self preservation:
- Identify danger and respond accordingly(spinal reflexes) - Voluntary movements:
- Getting from A to B
- Completing daily tasks - Homeostasis:
- Thermoregulation
- Glucose level control
What occurs during hypoglycaemia?
- Glucagon secreted by alpha cells of Islets of langerhans
- Glucagon travels around in blood
- Glucagon stimulates the breakdown of glycogen into glucose
How does endocrine communication work?
Hormones travel in the blood vessels to a target cell
What occurs during hyperglycaemia?
- Increased blood glucose levels leads to increased insulin secretion by beta- cells in the Islets of Langerhans
- Insulin has paracrine effect - inhibits glucagon secretion
- Insulin has endocrine effect on the liver
How does paracrine signalling work?
Hormones act on adjacent cells
How does membrane attached protein signalling occur?
Plasma membrane proteins on adjacent cells interact
How does autocrine communication occur?
Signalling molecules act on the same cell that it was produced by
How does neurotransmission occur?
- Voltage gated sodium channels open and cause depolarisation due to Na+ influx, which propagates the action potential. The voltage gated potassium channels then open which causes a K+ efflux which leads to repolarisation.
- The action potential results in voltage gated calcium channels to open on the pre-synaptic membrane. This leads to a Ca2+ influx which results in vesicle exocytosis, which contain neurotransmitter.
- The neurotransmitter bind to the post-synaptic membrane and receptors modulate post-synaptic activity
- The signal is then transmitted further by a variety of different receptor types.
What are the 4 types of receptor involved in neurotransmission?
- Ionotropic receptors
- G-protein couple receptor
- Enzyme-linked receptor:
- Ligand binding -> receptor clustering -> activates internal enzymes - Intracellular receptor:
- A membrane permeable ligand binds to receptor inside cell
How do ionotropic receptors work?
Ligand binding -> opens ion permeable pore to allow ions to move in and out based on their relative concentrations inside and out of the cell
How do G-protein coupled receptors work?
- 7-TM receptors and heterotrimeric G-protein receptors are inactive
- Ligand binding changes conformation of receptor
- Unassociated G-protein binds to receptor - bound GDP is phophorylated to GTP
- G-protein dissociates to:
- Alpha subunit
- Beta-Gamma subunit
- > These then bind to their target proteins - Internal GTPase activity on alpha subunit causes the dephosphorylation of GTP -> GDP
- Alpha subunit dissocaites from protein and become inactive again
- Receptor remains active for as long as the ligand is bound to it
How do enzyme-linked receptors work?
- Ligand binding -> receptors clustering
- Receptor clustering results in enzyme activation in cytoplasmic domain
- Enzymes phosphorylate receptor
- Phosphorylation -> binding of signalling proteins to cytoplasmic domain
- These signalling proteins -> recruit other signalling proteins -> signal is generated within cell
What 2 types of intracellular receptors are there?
Type 1 - Cytoplasmic
Type 2 - Nuclear
How doe Type 1 intracellular receptors work?
- Located in the cytosolic compartment
- Associated with chaperone molecules
- Horomone binds to receptor -> hsp dissociates
- 2 hormone bound receptors from a homodimer
- The homodimer translocates to the nucleus -> binds to DNA
How do type 2 intracellular receptors work?
- Located within the nucleus
2. Binding of hormone ligand -> transcriptional regulation
