Cell Receptors and Signal Transduction

How do cells communicate with one another

chemical messengers

receptor

area on the cell membrane that are sensative to chemicals and change behavior when activated

most receptors are

transmembrane proteins

where are the receptors that recognize lipid soluble messangers

the nuclear receptors inside the cell, recognize steroids

primary messanger

original chemical binding to the receptor

features of ligand protein binding

specificity affinity saturation competition

ligand specificity

ensures only certain messengers make a response, if structurally related will be close enough

agonist

chemical messanger that triggers normal response

antagonist

a molecule that binds and does not elicit a response, referred to as blockers

Example of drugs that are antagonists

beta blockers will reduce heart rate and contraction strength because receptors bind to beta blockers and reduce the response.

how can negative feedback be seen by receptors?

the number of receptors is not constant and changes over time in result to stimuli

down regualtion

high extracellular concentration of messanger leads to decrease in number of receptors

• decreased sensitivity

up regulation

when there is a low extracellular concentration number of receptors will increase

• increased sensitivity

signal transduction

messenger attaches to binding site changing the shape of protein eliciting a response

how does signal transduction start

receptor activation by a messeneger

types of signal transduction

lipid soluble primary messengers and water soluble primary messengers

lipid soluble primary messengers (genomic messangers)

move through bilayer through intracellular receptors

• alter rates of gene transcription and protein synthesis

water solible primary messenegrs

hydrophilic and cant pass throguh bilayers, activated rceptors lead to second messanger cascade makning the actual response.

types of water soluble primary messengers

• receptors that function as ion channles

• receptors that funciton as enzymes

• receptors that interact with cytoplasmic enzyme

  • receptros that interact with g protein

ligand gated ion channles

first messenger diffuses in and attaches to receptor opening the ion channel changing the electrical potential

• like acetylcholine receptors

receptor functioning as enzymes

binding of primary messsenger causes autophosphrylation which can then interact with second messenger inside the cell

• grwoth factor

receptors that interact with cytoplasmic enzymes

activated receptor binds to JAk which then phosphorylates second messanger cascade

• responses- cytokines and increased protein synthesis

EX JAK kianses

G protein coupled receptord

not a channle or enzyme, linked through G proteins to effector proteins or channles

G proteins contain

a b and gamma subunit

steps of g protein couplesd

A messenger minds and GTP replacees GDP on alpha subunit causing it to break off which then binds to an effector protien (ion channel) activating a cellular response (open or close)

what does CAMP do to g protein

act as second messenger

steps of CAMp

first messanger binds to g protein coupled receptor changing GDP to GTP and breaking off the alpha subunit which binds to adenylyl cyclase which turns ATP to CAMP which activates CAMP depndant protein kinases and then phosphorylate effectors tha induce response.

how does camp terminate signaling

converting to linear AMP by phoshphodiesterases or protein phosphotases

the more first messanger attaches to receptor

the more secnd messanger will be produced making a stronger cellular response

why does caffeine act as a stimulant

caffeine inhibits phosphodiesterase and prolongs CAMP activity acting as a stimualnt

What does camp dependant PKA do to ion channles

phosphorylates things, acts us indirect g protine gating

speeds of receptor activate on ion channel

ligand> gprotein coupled/ g ptroetin gates