Tissues 8 and 9 - Signalling between cells Flashcards
List the 4 reasons cells need to communicate
- Process Information
- Self preservation
- Voluntary movement
- Homeostasis
How does self preservation occur?
- Sensory stimuli are detected
- Spinal reflexes and the sympathetic nervous system allow us to appropriately respond to danger
Describe what happens when someone is hypoglycaemic.
- a cells in the islets of Langerhans secrete glucagon
- Glucagon travels through the blood vessels to the liver
- Glucagon causes glycogenolysis and gluconeogenesis
- Increases blood sugar levels
What type of signalling is occurring when glucagon acts on the liver cells?
Endocrine signalling
Define endocrine signalling.
Hormone travels within blood vessels to act on a distant target cell
Give some examples, not including glucagon action, of endocrine signalling.
- Insulin produced in the pancreas acts on the liver, muscle cells & adipose tissue
- Adrenaline produced in the adrenal glands acting on the trachea
Describe what happens in hyperglycaemia within the pancreas.
- B cells in the Islets of Langerhans secrete insulin
- Insulin inhibits glucagon secretion from the a cells
What type of cell signalling is insulin inhibiting glucagon secretion in the pancreas?
Paracrine signalling
Define paracrine signalling
The hormone acts on an adjacent cell
Give some other examples, not including insulin acting on the pancreas, of paracrine signalling.
- Nitric Oxide produced by endothelial cells in blood vessels
- Osteoclast activating factors produced by adjacent osteoblasts
Describe the process of TCRs binding to MHCs.
- Blood borne virus detected within blood stream by antigen presenting cell (APC)
- 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
Define cell communication by membrane-attached proteins
Plasma membrane proteins on adjacent cells interacting
Give an example of communication by membrane-attached proteins other than TCRs in immunity.
- Bacterial cell wall components bind to toll-like receptors on haematopoietic cells
Define autocrine signalling
The signalling molecule acts on the same cell.
List some examples of autocrine signalling
- Activated T cells express IL2 receptors on the cell surface, as well as secreting IL2 - so some of the IL2 will bind to the receptor
- Acetyl choline on presynaptic receptors
- Growth factors from tumour cells (mitogenesis)
List examples of intracellular signalling
- Ionotropic receptor
- G-protein coupled receptor
- Enzyme-linked receptor
- Intracellular receptor
Describe the process that occurs when a ligand sinds to an ionotropic receptor.
- Change in conformation of channel protein causing opening of a pore
- Pore allows ions to move in or out of cell according to their respective concentration gradients
List examples of ionotropic receptors.
- Nicotinic acetylcholine receptors in the skeletal muscle, which cause muscle contraction
- GABAa - uses a GABA ligand which decreases neuronal excitability
What do mutations in GABAa result in?
Seizures
Describe the process that occurs when G protein coupled receptors bind to a ligand.
- The receptor conformation changes
- The G-protein binds and GDP is replaced with GTP
- G protein dissociates into its alpha subunit and its beta/gamma subunits (attached)
- Each component binds to target proteins
- GTP is converted to GDP on the a-subunit
- The a-subunit dissociates from the target protein and becomes inactive
How long are G protein coupled receptors active?
They are active as long as receptors are bound
list the different types of Ga subunits.
Gs, Gi and Gg
Describe the function of Gs protein linked receptors
- They stimulate adenylyl cyclase
- Convert ATP to cAMP (cyclic adenosine monophosphate)
- cAMP activates PKA (protein kinase A)
Give an example of a Gs protein linked receptor
Beta 1-adrenergic receptors increase the heart rate
Describe the function of Gi protein linked receptors
- Inhibit adenylyl cyclase
- Reduce PKA levels (protein Kinase A)
Give an example of a Gi protein linked receptor
M2-muscarinic receptors decrease heart rate
Describe the function of Gg protein linked receptors
- Stimulates phospholipase C (PLC) - PIP2 –> IP3 + DAG
- IP3 stimulates Ca2+ release
- DAG activates PKC
Give an example of a Gg protein linked receptor
AT-1 angiotensin receptor causes vasoconstriction
Describe the structure of a G-protein linked receptor
- 7-TM proteins (transmembrane)
- Extracellular ligand-binding N-terminus
- Intracellular G-protein binding C-terminus
Describe the process that happens to enzyme-linked receptors once the ligand has bound
- More than one receptor
- Receptor clustering activates enzyme activity within cytoplasmic domain - Enzymes phosphorylate receptor
- Binding of signalling proteins to cytoplasmic domain
- These signalling proteins recruit other signalling proteins
- Signal is generated within cell
What is another name for enzyme-linked receptors?
Tyrosine kinase receptors
Give examples of enzyme-linked receptors.
- Insulin receptor causes glucose uptake
- ErbB receptors (growth and proliferation)
- Guanylyl-cyclase linked receptors
- Ser/Thr-kinase linked receptors
What are the two types of intracellular receptors?
Cytoplasmic and Nuclear
How do cytoplasmic intracellular receptors work?
- Located within the cytosolic compartment
- Associated with chaperone molecules (heat shock proteins, hsp) - Hormone binds to receptor, chaperone dissociates
- 2 hormone bound receptors form a homodimer.
- The homodimer translocates to the nucleus and binds to DNA
How do nuclear cytoplasmic intracellular receptors work?
- Located within the nucleus
- Binding of hormone ligand
- Transcriptional regulation
Give an example of a cytoplasmic intracellular receptor.
- Glucocorticoid receptor - uses corticol and corticosterone
- Reduce the immune response and increase gluconeogenesis
Give an example of a nuclear intracellular receptor.
- Thyroid hormone receptor
- Binds to Thyroxine (T4) and triiodothyronine (T3)
- Causes growth & development
