hormones and cell signalling Flashcards
how do signalling molecules work
- receptors are expressed by target cells
- if no receptor exists for a given signal, there is no response
- ligands are the signalling molecules
- ligands bind to a site on the receptor
what is autocrine signalling
affects the cell producing them
what is paracrine signalling
diffuse short distance to affect cells nearby
what is endocrine signalling
acts on target cells distance from site of synthesis
what are the consequences of cell signalling
- survival
- divide
- differentiate
- die
what are the 2 types of hormones
- lipid soluble
- water soluble
discuss lipid soluble hormones get around and act
- transported in blood by carrier proteins
- diffuse through plasma membrane
- alter expression of genes at level of nucleus
discuss water soluble hormones get around and act
- easily travel in the blood (hydrophilic)
- bind to receptors on the surface of the cell
- results in series of of intracellular events
what happens when a hormone binds to its nuclear receptor
hormone plus receptor activates receptor, active receptor binds to DNA to turn the genes on or off
regulates transcription of specific target genes
what is the function of nuclear receptors
in the presence of their hormones, the nuclear receptor recruits additional coactivator proteins which then regulate the activation and repression of nearby target genes
list intracellular signal transduction pathways (water soluble)
- adenyl cyclase
- guanyl cyclase
- phospholipase
- tyrosine kinase
- ion channels
what are the 3 components of a membrane receptor
- external domain
- transmembrane domain
- cytoplasmic/intracellular domain
how does termination of hormone signalling work
- once the signal is withdrawn, the response fades
- depends on rate of destruction or removal of molecules that the signal affects
- but the turnover rate also depends on promptness of response when a signal is turned on
- these factors determine the half-life of the signalling molecule (T1/2)
what does T1/2 refer to
- time taken for the concentration of a signalling molecule to fall by half
- transient signals may have long lasting effects
- determined by rate of synthesis and modifications of proteins
what are the main classes of cell surface receptors
- ion-channel linked receptors
- G-protein linked receptor
- tyrosine kinase-linked receptor
- receptors with intrinsic enzymatic activity
explain how ion channel surface receptors work
- signal molecule binds to receptor
- this opens or closes the ion channel
- ions move into the cell by diffusion
- excitability of post-synaptic cell altered
describe second messenger signalling
- second messengers are small intracellular signalling molecules
- generated in large numbers by receptor activation (amplification of signal)
- rapidly diffuse away
- pass signal on by binding to and altering behaviour of other proteins
- exhibit different ways of passing signal on
list functions of intracellular proteins
- scaffolding (brining signal to other proteins)
- relays
- adaptors (bring proteins together)
- amplifiers
- modulators
list key processes in cell signalling
- protein phosphorylation (via protein kinases)
- ## reversal of protein phosphorylation (via phosphoprotein phosphatase)
what does phosphorylation alter
- enzyme activity
- protein stability
- protein interactions
what are the steps of G protein mediated signal transduction
- no ligand = inactive receptor
- binding of ligand recruits the G protein complex
- GTP replaces GDP (activates G protein)
what are the 6 classes of enzyme linked receptors
- receptor tyrosine kinases (phosphorylate on intracellular signalling molecules)
- tyrosine-kinase associated receptors (associate with intracellular proteins with tyrosine kinase activity)
- receptor-like tyrosine phosphatases (remove phosphate groups from tyrosine on intracellular proteins)
- receptor serine/threonine kinases (phosphorylate serines or threonines on regulatory proteins)
- receptor guanyl cyclases (catalyse production of cytosolic cGMP)
- histidine kinase associated receptors (two component system: kinase phosphorylates itself and passes on phosphate to intracellular signalling protein)
