concept 12 - BIO10008

Describe 3 functions of cell-to-cell communication and give an example of each one being used by a living organism.

signalling to regulate their metabolism

feedback mechanisms

cells maintaining energy balance with exergonic and endergonic reactions

True or false? Justify your response. “The extracellular signal molecule acetylcholine has different effects on different cell types in an animal and often binds to different cell-surface receptor molecules on different cell types

True, because acetylcholine is a neurotransmitter and can have different effect depending on which neuron required to send the signal either to muscle or regarding digestion. Also, since it is an extracellular signal molecule, they bind to cell-surface receptor molecules.

signal perception

signal perception is when a ligand binds to a receptor that is specific for the ligand. This allows a detection in the signal.

signal transduction

the extracellular signal molecule is converted into a intracellular signal molecule which goes inside the cell in a relay, there is a sequence of change involved and the shape of the tertiary protein is changed to allow transduction.

this begins a cascade of intracellular signalling events (transduction cascade)

cellular response

signaling events finally trigger a specific cellular activity to allow activation of cellular response

second messagers

amplifies the signal and activates multiple pathways

compare and contrast signalling by neurons which secrete neurontransmitters at synapses with signalling carried out by endocrine cells, which secrete hromone into the blood.

signalling in neurons are instantaneous and take very short time as it transmits electrical signals, (short range messenger) whilsts signalling carried out by endocrine cells, have to travel a distance to reach its receptors thus the time the signal can emit a cellular response is longer compared to neurotransmitters. (long term messenger)

In addition, neurons are synaptic signalling

enzyme coupled receptor

extracellular receptor, embedded in the plasma membrane, will have phosphorylation of an intracellular protein (EGF receptor)

GPCR (Gprotein)

imbedded in the plasma membrane and binds to G protein inside to activate the protein which induces a internal signal response. (Epinephrine receptor)

ligand gated ion channel

embedded on the plasma membrane, opens an ion channel when activated and allows ions to pass through. (acetylcholine receptor)

intracellular receptor

inside the plasma membrane, in the cytosol or nucleus and turns on the transcription of specific genes (estrogen receptor) the signal must be non polar so it can diffuse across the membrane