Tissues 8-9 Flashcards
Why do cells need to communicate?
- Sensory stuli
- Survival (reflexes etc)
- Voluntary movement
- Homeostasis
What is endocrine signalling?
Hormone that travels via the blood vessels to act on distant target cells.
What is paracrine signalling?
Hormones that acts on the adjacent cell.
What is autocrine signalling?
Hormone that acts on the cell or cell type that produced it.
Example of autocrine signalling?
Activated T-lymphocytes produce IL-2 which then acts upon other T cells.
Example of paracrine signalling?
Insulin is produced by beta cells that then goes to act on the adjacent alpha cells in the pancreas.
Example of endocrine signalling?
Insulin produced in the pancreas acts upon the liver, adipose and muscle tissue.
What is an ionotropic receptor?
Receptor opened by ligand binding, causing the opening ion permeable pores in the membrane.
Examples of ionotropic receptors?
Nicotinic acetylcholine (muscle contraction) and GABAa receptors (decrease neuronal activity)
What is an enzyme-linked receptor?
Receptor opened by ligand binding causing clustering of receptors, activating internal enzymes.
How do enzyme-linked receptors work?
1) Ligand binding causes clustering
2) Clustering activates enzymes, causing phosphorylation of the receptor
3) Phosphorylation causing binding of signalling proteins in cytoplasm
What is an intracellular receptor?
Located on the inside of a cell so that only membrane-permeable ligands can bind to it.
How do intracellular receptors work?
(Type 1)
1) Hormone binds to receptor, causing HSP chaperone molecule to dissociate
2) Two receptors form homodimer
3) Homodimer translocates to nucleus and binds to DNA, influencing transcription and translation
(Type 2 are located in the nucleus)
How do G-protein coupled receptors work?
Ligand binding activates intracellular G-protein pathways.
How do G-protein coupled receptors work?
1) Ligand binding activates 7-TM receptor, changing its conformation of internal region so ligand stays bound.
2) Unassociated G-protein binds to receptor and causes GDP to be phosphorylated to GTP
3) The new GTP molecule provides energy to split the G-p into alpha and beta subunits (G-p stays with alpha subunit)
4) Alpha subunit binds to intracellular proteins, initiating signalling process
5) GTP is reversed to GDP
6) Subunits reassociate and become inactive
