Molecular Interactions in Cell events

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Molecular Interactions in Cell events

1. Catalysis
2. The Sodium-Potassium Pump
3. Cell Signalling

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Alien Invasion

• Alien customs
• What does this have to do with cell signalling?

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
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Cell Signalling general principles

• 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.

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Extracellular hydrophobic signalling molecules

• 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

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Extracellular hydrophobic signalling molecules
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Extracellular hydrophilic signalling molecules

• 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
• Ion-channel linked (chemically-gated ion
  channels)
• Enzyme linked
• G-protein linked

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Extracellular hydrophilic signalling molecules

• Ion-gated channels
• Signal molecule binds
• Changes the shape of a protein channel, which
  opens
• Ions flow in through the open protein gate
• Example
• 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.

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Extracellular hydrophilic signalling molecules

• Enzyme-linked receptors
• 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

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Extracellular hydrophilic signalling molecules

• Enzyme linked receptors
• Example
• 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

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Extracellular hydrophilic signalling molecules

• G-protein linked receptors
• 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)

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Extracellular hydrophilic signalling molecules

• G-protein linked receptors
• Example
• 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

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Summary
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Learning Activities

• 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/Sigtr
  anRA.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?