Biological signalling Flashcards
what are signals
- represent information that is detected by specific receotors
- Signals are converted to a cellular response which always involves a chemical process
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what is signal transduction
Conversion of information into chemical change
what is specificity
- singal molecule fits binding site on its complementary receptor; other signlas do not fit
* Multicellular organisms have additional specificity: Some receptors are present in only certain cell types
what are the 3 factors accounting for sensitivity of signal transducers
- High affinity of receptors for signal molecules (Kd = 10-10 M)
**small [L] → large activation response (only need tiny amount bc hugre affinity)
- Cooperativity in the ligand-receptor interaction
- Once activated, signal amplification occurs through by enzyme cascades
explain amplification
Amplifications of several orders of magnitude within milliseconds = FAST RESPONSE
*one signalling molecule bidns to one receptor, receptor then activate then can activate other things)
- amplification= when enzymes activate enzymes, the number of affected molecules increases geometricaly in an enzyme cascade
what is modularity
- proteins with multivalent affinities from diverse signalling compleses from interchangable aprts
- phosphorylation provides reversible points of interaction
explain desensitization/adaptation
- receptor activation triggers a feedback circuit that shuts off the receptor or removes it from the cell surface
- When stimulus falls below a certain threshold the system again becomes sensitive
explain integration of signas
- when two signals have opposite efects on a metabolic characteristic such as the concentration of a second messengerX or the mebrane potential Vm the regualtory outcome results from the integrated input from both receptors
- Integration produces a unified response appropriate to the needs of the cell or organism
what is a G protein coupled recpetor
- external ligand [L] binding to receptor [r] activates an intracellular GTP bidning protein (G)
- this regualtes an enzyme that generates an intracellular second messanger
- ligand bidning usually causes confomrational change
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what are receptor tyrosine kinases
0 integral mem rptoin on plasma memrbane
- ligand binds and activates tyrsoine kinase activity by autophosphorylation
*RTK become an active kinase itself
what are receptor guanylyl cyclase
- ligand binding to extracellular domain stimulates formation of second messenger cyclic GMP
what are gated ion channels
- open or close in resonde to concentration of signal ligand or memrbane protential
what is an adhesion receptor
- integrin
- binds molecules in extracellular matrixm changes conformation altering interaction with cytoskeleton
*if cell wants to move thru environment must removed the cytoskeleton, so you have integrin recpetors that can bind and interact with components of ECM leading to cahnges in shape of the cell
what are nuclear recetors
- hormone bidning allows the receptor to regulate the expression of specific genes
ion gradients in neurons and transmission of a nerve impulse
- Neuron cytosol has high [K+] and low [Na+]
- At rest, ΔΨ = -60 mV
Transmission of a Nerve Impulse
(i) action potential carries electrical signal down axon
(ii) neurotransmitter carries signal to next cell
explain Nicotinic acetylcholine receptor (AchR)
- Passage of electrical signal from motor neuron to muscle fiber at neuromuscular junction
- Acetylcholine released by motor neuron diffuses to plasma membrane of a myocyte → binds AchR
• Conformational change in AchR → opens
→ inward movement of cations (Na+, Ca2+)
→ triggers muscle contraction