Chemical Signalling Flashcards
(21 cards)
What is a ligand?
A molecule that binds selectively to a specific site on another molecule
Key differences between enzymes and receptors?
- Enzyme-substrate binding is brief and other substrates can bind immediately after release. A ligand, on the other hand, can bind for longer periods
- Substrates are changed into the product and released, the ligand is released as is after the signal is conveyed
What is quorum sensing?
Quorum sensing is a regulation of gene expression at a particular population density in cells based on the number of cells that have received the signalling chemical.
What is quorum sensing an example of?
Interaction - signal molecules pass from cell to cell
Interdependence - only effective if more than one cell is involed
What are the effects of the rapid breakdown of neurotransmitters?
Effect of neurotransmitters are short lived
Ensures restriction to one post-synaptic neuron
What is a cytokinin?
A small protein that acts as a signalling molecule. Binds to transmembrane receptors
Effects of cytokinin?
Causes cascade of signaling leading to changes in gene expression and subsequent cell activity.
It can bind to several types of receptors and so has multiple effects
Roles in inflammation and other immune system responses
Control of cell growth and proliferation in embryo development.
Examples of cytokinins ?
Erythropoietin, interferon, interleukin
Requirements for a signalling chemical?
- must have a distinct shape and chemical properties so that the receptor can distinguish between it and other chemicals
- must be small and soluble enough to be transported
What are the two types of receptors?
Intracellular receptors - for the ligands which can pass through the membrane. present in the cytoplasm or nucleus. Remain dissolved in aqueous fluids
Transmembrane proteins - in the plasma membrane for ligands that cannot enter cells. Both hydrophobic and hydrophillic.
How does binding take place in an intracellular receptor?
When the ligand binds to the intercellular receptor, it forms an active ligand-receptor complex. Binds to DNA at specific sites and promotes or inhibits transcription of particular genes.
How does binding take place in an transmembrane receptor?
ligand binds to transmembrane receptor - receptor produces secondary messenger - messenger activates effector to carry out responses to the signal
What is GDP
Guanosine Diphosphate
Explain signal transmission by G-protein-coupled receptors
A G protein has three subunits. A GDP molecule is bound to the subunit. This keeps it inactive. A ligand binds to the receptor causing conformational changes. GDP detaches - GTP attaches. Activates receptor. subunits dissociate from receptor and convey signal brought by the ligand within the cell.
Explain the mechanism of action of epinephrine receptors.
Epinephrine binds to transmembrane receptor - changes the shape - activates G protein - activates enzyme adenylyl cyclase in the membrane - converts ATP to cATP = secondary messenger - amplifies signal - large process is triggered.
What is a kinase?
A kinase is an enzyme that adds a phosphate group from ATP to a specific molecule
tyrosine kinase mechanism
insulin receptor - activated by binding of insulin - two tyrosine kinase proteins connect to form a dimer - biochemical chain of events - vesicles containing glucose transporters fuse with membrane, inserting transporters - allow glucose in by facilitated diffusion
Effects of oestradiol
During and before ovulation - it promotes the release of GnRH. binds to receptor in hyothalamus. complex moves to nucleus and enhances trnascription of GnRH
Calcium-induced-calcium release
binding of inositol triphosphate (IP3) to the receptor causes partial release of Ca. increase activates IP3 receptor on neighboring channel causing further release of Ca
Release of testosterone - negative cycle
GnRH releases LH, LH stimulates release of testosterone. Testosterone signal to anterior pituitary to stop LH. signal to hypothalamus to stop GnRH
Explain Bioluminescence as a mechanism of Quorum Sensing
In Vibrio Fischeri cells, quorum sensing is used as a mechanism of regulation of gene expression. The Vibrio cells produce a signalling molecule known as a “autoinducer”. When produced the autoinducer cells are sent into the external environment. When the vibrio cells start reproducing, the number of cells increase and subsequnetly the amount of autoinducer also increases. When it reaches a certain threshold, the autoinducers renenter the bacteria and bind to a protein called the LuxR protein. Which binds to a DNA site called the luxe box. This leads to the production of luciferase - an enzyme which helps to illuminate the bottom of the squid to match the sun.
- protects from predators
- saves energy
