Extracellular Signalling Flashcards
What are the two communication systems?
Hormonal and nervous system.
Why is important that cells communicate with one another?
Integration and coordination would be impossible.
What happens with regards to extracellular signalling molecules?
One cell releases a chemical signal molecule and another cell detects and responds to it. Theses cells may be close neighbours or may be in quite different locations within the organism. Either way, the signal has to leave one cell and travel to another- the target cell.
What can the same signal stimulate?
Many different target cells in different ways, also the same target cell may have a various receptors, each is specific to a different signalling molecule, therefore allowing the cell to respond to many different instructions.
What are hormones?
Extracellular signalling molecules that are secreted by one tissue into the blood. The hormone circulates in the bloodstream until it reaches it’s target receptor or is broken down.
What two categories do the signalling mechanism of a hormone fall into?
Hydrophilic hormones and hydrophobic.
What are hydrophobic hormones?
Peptide hormones such as insulin, ADH and growth hormone.
What are hydrophilic hormones?
Steroid hormones such as testosterone.
What are neurotransmitters?
The signalling molecules released during nervous communication are known as neurotransmitters. Neurotransmitters are hydrophilic molecules and they are released into the synaptic cleft between nerve cells and their neighbours. In comparison with hormonal communication, nervous communication is very specific due to this intimate association between the signalling cell and the target cell.
What effect does an extracellular signalling molecule have when it binds to its specific receptor molecule?
Just an effect
Where are hydrophobic signalling molecules receptors?
As they can pass through the membrane this receptor molecules are within the cytoplasm or the nucleus of the target cell.
Where a the receptor molecules for hydrophilic signalling molecules?
As they cannot pass through the membrane their receptors are integral proteins.
What are hydrophobic molecules?
Lipid soluble so they are able to move by diffusion across the hydrophobic part of the plasma membrane. The receptors for hydrophobic extracellular signalling molecules are, therefore, deep in the cytoplasm or nucleus of the target cell. The receptor for a steroid hormone is a gene-regulatory protein which changes conformation when the steroid binds to it. This conformation change activates the protein so that it can bind directly to the DNA and the regulate the transcription of specific genes.
What is an example of a steroid hormone?
Testosterone, progesterone and oestrogen. Each one shares the common four-ringed structure of steroids by varies in its side chains.
What are hydrophilic molecules?
They are not lipid soluble and cannot pass through the hydrophobic barrier of the cell membrane. Instead, they bind to a transmembrane protein receptor at the cell surface. Once the signal molecule binds to the protein at the surface of the cell, the conformation of the transmembrane protein alters in some way. This results in signal transduction into the cell, changing the behaviour of the cell. An ion channel at the cell surface mag open or a secondary messenger within the cell cytosol may be released. Secondary messengers can alter cell behaviour by activation of proteins by kinase enzymes and phosphorylation, or through pathways involving calcium ion release from the endoplasmic reticulum.
