Molecular Interactions in Cell
events
(i)
(ii)
(iii)
Catalysis
The Sodium-Potassium Pump
Cell Signalling
Alien Invasion
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Alien customs
Gesture
Meaning
Smile
A sign of violence or a
threat
Wave
Go away
Handshake
Gesture of love
Being higher than the
person
Insult
Hello / how are you /
welcome
You smell
What does this have to do with cell signalling?
Cell Signalling – general principles
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Communication is usually achieved through
hormones or nerve impulses
Signal is sent by a signalling cell
Signal is received by a target cell
Any change in signal type is called signal
transduction
A signal transduction pathway is a series of
responses to the bonding of a signal molecule
All receptor proteins have an active site. They are
specific to signal molecules. Therefore, signals will
only act on target cells that have these receptors.
Extracellular hydrophobic signalling
molecules
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Hydrophobic molecules can dissolve in the
plasma membrane and move into a cell by
diffusion
Examples: steroids e.g. testosterone
Target cells have a specific hormone receptor
The hormone binds and activates the receptor
Hormone – receptor complex binds to gene
regulatory sites
Stimulates the transcription of certain genes
Extracellular hydrophobic signalling
molecules
Extracellular hydrophilic signalling
molecules
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Have charged surfaces, therefore cannot
dissolve in cell membrane
Are too large to pass through protein channels
Bind and change the shape of proteins on the
surface of the target cell
There are three types of receptor protein
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Ion-channel linked (chemically-gated ion channels)
Enzyme linked
G-protein linked
Extracellular hydrophilic signalling
molecules
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Ion-gated channels
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Signal molecule binds
Changes the shape of a protein channel, which
opens
Ions flow in through the open protein ‘gate’
Example
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Nerve cells
Neurotransmitters e.g. acetylcholine or noradrenalin act
as signal molecules
Opens ion gate to allow transmission of a message from
one neuron to another.
Extracellular hydrophilic signalling
molecules
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Enzyme-linked receptors
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A receptor-enzyme complex spans the
membrane, with the enzyme on the inside
The enzyme is inactive
The signal molecule binds to the receptor, which
then activates the enzyme
Extracellular hydrophilic signalling
molecules
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Enzyme – linked receptors
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Example
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Tyrosine-Kinase receptor
Signal molecules are insulin and growth hormone (both
peptide hormones)
Activates the complex and kinase activates other
enzymes through phosphorylation
Ultimately gene regulation proteins are switched on
resulting in different gene transcription
Extracellular hydrophilic signalling
molecules
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G-protein linked receptors
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Receptor molecule spans the membrane, with a
G-protein attached on the inside
Signal molecule binds to the receptor and causes
a molecule called GTP to activate the G-protein
The activated G-protein moves along the plasma
membrane and activates an enzyme (or
sometimes an ion channel protein)
Extracellular hydrophilic signalling
molecules
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G-protein linked receptors
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Example:
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Signal molecules can include glucagon and adrenaline
(both peptide hormones)
After G-protein and enzyme are activated the enzyme
releases second messenger molecules (e.g. cyclic AMP or
Ca2+)
Second messengers phosphorylate and activate kinase
enzymes
These activate more kinase enzymes
With glucagon, the final set of kinase enzymes activated
convert glycogen to glucose-1-phosphate
Summary
Learning Activities
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Read DART pg 70 – 72
Scholar 7.2 – 7.3 (7.1 to a lesser extent)
Advanced Higher Questions
Draw a diagram / make a poster to explain the steps in
extracellular hydrophobic signalling
Draw flow charts to show the processes in extracellular
hydrophilic signalling
Revise the biology behind each of the examples given
http://www.sp.uconn.edu/~bi107vc/images/anim/SigtranRA.gif
Do your own internet search to find info. Remember to evaluate
the site – Who is the author? Who are the intended audience?
When was it last updated?