Unit 1 - Test 2 Flashcards
what do multicellular organisms use to signal between each other?
extra-cellular molecules
examples of extra-cellular signalling molecules
hormones (steroid + peptide), neurotransmitters
what are receptor molecules on target cells?
proteins with a binding site for a specific signal molecule.
binding changes the conformation of the receptor, which initiates a response within the cell
variation in responses?
different cell types may show a specific and different tissue response to the same signal
steriod hormones
- are lipophilic so can freely diffude across the membrane
- they bind to nucleus or cytoplasm of target cell
- examples include oestrogen and testosterone
- hormone-receptor complex moves to the nucleus where it bonds to specific sites on DNA and affects gene expression
- specific DNA sites are called hormone response elements (HREs), binding here influences the rate of transcription
peptide hormones
- they are lipophobic (fat-hating) so cannot freely diffuse across membrane
- bind to specific receptors on the surface of target cells
neurotransmitters
- chemical messengers
- transmit messages over much shorter distances than hormones
- carry messages across the synapse
hydrophobic signalling molecules
- able to directly diffuse through the phospholipid bilayer
- once inside cell they bind to intracellular receptors
- these intracellular receptors are 𝐭𝐫𝐚𝐧𝐬𝐜𝐫𝐢𝐩𝐭𝐢𝐨𝐧 𝐟𝐚𝐜𝐭𝐨𝐫𝐬
hydrophilic signalling molecules
- bind to transmembrane receptors
- conformational change of receptor after ligand binds
*signal molecule is tranduced across the plasma membrane; transmembrane receptors act as signal transducers by converting the extracellular ligand-binding event into specific intracellular signals, altering the behaviour of the cell
transduction
- involves a series of reactions that occur inside the cell through a signal transduction pathway
- transduced hydrophilic signals often involve G-proteins or cascades of phosphorylation by kinase enzymes
G- proteins
- relay signals from activated receptors to target proteins (e.g. enzymes and ion channels)
- they are a family of proteins that act as molecular switches inside cells, involved in transmitting stimul from outside to the interior of the cell
transduction by phosphorylation cascades
- involves a series of events with one kinase activating the next in the sequence, and so on
- can result in the phosphorylation of many proteins
GLUT4 proteins
- glucose transporters
- binding of insulin to GLUT4 receptor triggers phosphorylation of this receptor, starting a 𝗰𝗮𝘀𝗰𝗮𝗱𝗲 within the cell
- eventually leads to GLUT4-containing vesicles being transported to the membrane to increase GLUT4 activity in the membrane
what is a transcription factor?
a protein, when bound to DNA, will either activate or inhibit transcription
what is resting membrane potential?
a state where there are no net flow of ions across the membrane