BIOL 22000 Chapter Notes - Chapter 8: Membrane Protein, Action Potential, Agonist
Lecture 8
• How do cells pick up information from the environment and respond appropriately?
o Fundamental problem for all life
o Cells need to translate an external signal into an internal change
o Cells can electrical or chemical to relay messages, sometimes over long distances
o Similar messages used in all forms of multicellular life
Within A Single Cell
Between Cells
Electrical Communication
Action Potential, Graded
Potential
Electrical Synaptic
Transmission
Chemical Communication
Cell Signaling
Chemical Synaptic
Transmission, Endocrine
Signaling
• Basics of Cellular Signaling
o Cellular processes can change in response to both chemical and electrical
signaling
▪ Example of electrical signaling is graded potential can change
permeability of the cell to ions
o Chemical signaling requires receptor
▪ A protein act as a receptor to bind to the initial chemical signal
o The chemical that interacts with the receptor is called a ligand
▪ Sometime ligand is called first messenger
o Both endogenous and exogenous ligands can activate receptors
▪ Endogenous: a molecule that is produced within your own body
▪ Exogenous: a molecule that comes from outside the body and can bind to
your receptor
▪ Sometime more then one of these can activate the receptor
o The specific cellular responses to the ligand are determined by the
receptor, NOT ligand
▪ Sometime the protein that relay the message from the receptor to the rest
of the cell can also determine the response
o In most cases, the chemical message is relayed within the cell and
translated into cellular change using positive feedback
• The flow chart
o First a receptor protein, either endogenous or exogenous ligand, aka first
messenger, binds to a receptor protein
o The receptor protein is usually found on the cell membrane
o The binding of the ligand to causes conformation for the receptor protein
▪ This cause signaling cascade of changes to other protein and molecules
o The activates signal molecule alters the target protein
▪ Example: protein that is more transcription or translation, ion channel.
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•
o The first one is simply an ion channel and bypasses all the middle step
▪ A chemical bind to the receptor and causes a chemical change, and the
receptor open and closes
▪ Produced a change right there
o The second one is called G-Protein receptor
▪ A receptor binds to the outside of the protein and cause a conformational
change
▪ The conformation change also causes the conformation for the protein that
is associated with the intracellular side of the receptor, aka G-Protein
▪ G-Protein is like a relay mechanism that activates the other changes in the
cell
o The third one is called Receptor-Enzyme
▪ The receptor itself has enzymatic activity
▪ When the ligand binds to the receptor on the ECF, it activates the enzyme
activity in the ICF
▪ A lot of time the activity is kinase activity, that means when activated the
intracellular part can add phosphate group to different molecule/receptor
▪ The present/removal of the phosphate is associated with active and
inactive
o The forth one is Integrin Receptor
▪ The ligand attached to the receptor translate to a change in cytoskeleton, to
allow the cell to move and change shape
▪ NOT TALKED ABOUT
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•
o Receptor Channel: nAChR
▪ The receptor is going be usually bound by an endogenous ligand called
acetylcholine (neural transmitter)
▪ Since is an ion channel, it skips some of the steps on the flow chart, such
as intracellular signal molecules
▪ Nicotinic Acetylcholine receptors is expressed on skeletal muscle cells
▪ Receptor is nonselective cation specific ion channel
• Let any cation ion through, such as potassium and sodium
▪ Ligand binding opens channel
▪ Increased membrane permeability to both K+ and Na+
▪ Depolarizing graded potential
▪ Muscle contraction
▪ Most cells have higher permeability to potassium then to sodium
o
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