Extracellular Signalling Flashcards
What are the two principle forms of communication in multicellular organisms?
Nervous and Hormonal
What is the function of an extra cellular signalling molecule?
Cell releases the molecule that another cell detects and responds to.
Why is the communication between cells important?
To make possible the integration and coordination of cellular activities
What are extracellular signalling molecules?
Signals which originate from outside the target cell
How can a target cell respond to many different instructions?
Signal molecules can stimulate different target cells in different ways, and the target cell may have many receptors, each specific to a different signalling molecule.
What are hormones?
Extra cellular signalling molecules that are secreted by one tissue into the blood.
When does the hormone leave the blood stream?
When the hormone reaches the target receptor or is broken down
Give examples of hydrophobic and hydrophilic hormones.
Hydrophilic: Peptide hormones such as Insulin, ADH, and HGH
Hydrophobic: Steroid hormones such as testosterone.
What are neurotransmitters?
The signalling molecules released during nervous communication.
What type of molecule are neurotransmitters?
Hydrophilic
Where are neurotransmitters released?
Into the synaptic gape between a nerve cell and its neighbour
Why is nervous communication considered very specific in comparison to hormonal communication?
Due to the intimate association between the signalling cell and the target cell.
When does an extra cellular signalling molecule cause an effect?
When it binds to its specific target receptor molecule
Where do you find the receptor molecules for hydrophilic and hydrophobic signalling molecules?
Hydrophobic signal molecules : Within the nucleus or cytoplasm
Hydrophilic: They are integral proteins as they cannot pass through the plasma membrane
Why can hydrophobic molecules pass through the plasma membrane?
They are lipid soluble and so are able to move across the hydrophobic part of the membrane by diffusion.
What is the receptor for a steroid hormone?
A gene-regulatory protein
What happens when the steroid binds to the gene-regulatory protein?
It causes a conformational change to the protein, activating it and allowing it to bind directly to the DNA and regulate the transcription of specific genes.
What happens when a hydrophilic signal molecule binds to the integral protein?
The conformation of the transmebrane protein alters in some way. Resulting in signal transduction into the cell and a change in the behaviour of the cell.
What may be the result of cell transduction into the cell?
An ion channel at the cell surface may open or a secondary messenger within the cell cytosol may be released.
How can secondary messengers alter cell behaviour?
By activation of proteins by kinase enzymes and phosphorylation.
Through pathways involving involving calcium ion release from the endoplasmic reticulum.
What does each peptide hormone require?
A specific receptor protein at its target cells surface.
Why can the action of peptide hormones be highly specific?
Since only the target cells have the appropriate receptors at their surface.
Give examples of neurotransmitters
Acetylcholine + noradrenaline (hydrophilic peptides)
What is acetylcholine?
The transmitter at the neuromuscular junction connecting motor nerves to muscles
Give information about noradrenaline
HAs a role in the central nervous system and the sympathetic nervous system. Usually noradrenaline can also act as a stress hormone if released into the blood.
