Cell Signalling
CS1. Stages of Cell Signalling
Ligand-Receptor interaction
• Ligands (eg. Hormones, amino acids, etc.) can bind to the complementary ligand-
binding site of a speci c receptor
• Receptors will transduce the message of the signal molecule into a cellular response
• Binding of the ligand to its speci c receptor will activate the receptor proteins by
inducing a conformational change in the intracellular domain of the receptor
• The ligand-receptor interaction is speci c because the ligand is complementary in
charge and shape to the ligand-binding site of the receptor
Cell surface receptors are transmembrane proteins located on the plasma membrane and
can bind to large/hydrophilic/polar signal molecules that cannot di use readily across the
hydrophobic core or pass through the transient pores of the phospholipid bilayer.
• G-protein-coupled receptors
• Enzymatic receptors (receptor tyrosine kinase)
• Chemically-gated ion channels
Signal Transduction
• Refers to a series of changes in cellular proteins that converts extracellular chemical
signals into a speci c intracellular response, such as by activating other relay
proteins through a phosphorylation cascade and signal ampli cation
A phosphorylation cascade is a sequence of events where one enzyme phosphorylates
another, causing a chain reaction leading to the phosphorylation of thousands of proteins.
Phosphorylation/dephosphorylation is a post-translational medication for controlling
protein function. Kinase (an enzyme) adds phosphate groups from ATP to the protein and
activates them, while phosphatase (an enzyme) removes phosphate groups from proteins
via hydrolysis to deactivate them.
Signal application produces a large number of intracellular mediators from a small number
of intracellular signal molecules to bring about a large response. Protein kinases are
usually involved since they catalyse the phosphorylation of speci c proteins to activate
them.
Cellular Response
• Includes regulation of gene expression (up or down regulation) and metabolic
pathway regulation for activation/inhibition of enzymes
• Di erent responses can be brought about by the same ligand and receptor due to
di erent genes being expressed, which allows for di erent relay molecules and signal
pathways in di erent cells
• Essentially, di erent cells can have di erent responses to the same signal and same
cells can have the same response to di erent signals
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CS1. Stages of Cell Signalling
Ligand-Receptor interaction
• Ligands (eg. Hormones, amino acids, etc.) can bind to the complementary ligand-
binding site of a speci c receptor
• Receptors will transduce the message of the signal molecule into a cellular response
• Binding of the ligand to its speci c receptor will activate the receptor proteins by
inducing a conformational change in the intracellular domain of the receptor
• The ligand-receptor interaction is speci c because the ligand is complementary in
charge and shape to the ligand-binding site of the receptor
Cell surface receptors are transmembrane proteins located on the plasma membrane and
can bind to large/hydrophilic/polar signal molecules that cannot di use readily across the
hydrophobic core or pass through the transient pores of the phospholipid bilayer.
• G-protein-coupled receptors
• Enzymatic receptors (receptor tyrosine kinase)
• Chemically-gated ion channels
Signal Transduction
• Refers to a series of changes in cellular proteins that converts extracellular chemical
signals into a speci c intracellular response, such as by activating other relay
proteins through a phosphorylation cascade and signal ampli cation
A phosphorylation cascade is a sequence of events where one enzyme phosphorylates
another, causing a chain reaction leading to the phosphorylation of thousands of proteins.
Phosphorylation/dephosphorylation is a post-translational medication for controlling
protein function. Kinase (an enzyme) adds phosphate groups from ATP to the protein and
activates them, while phosphatase (an enzyme) removes phosphate groups from proteins
via hydrolysis to deactivate them.
Signal application produces a large number of intracellular mediators from a small number
of intracellular signal molecules to bring about a large response. Protein kinases are
usually involved since they catalyse the phosphorylation of speci c proteins to activate
them.
Cellular Response
• Includes regulation of gene expression (up or down regulation) and metabolic
pathway regulation for activation/inhibition of enzymes
• Di erent responses can be brought about by the same ligand and receptor due to
di erent genes being expressed, which allows for di erent relay molecules and signal
pathways in di erent cells
• Essentially, di erent cells can have di erent responses to the same signal and same
cells can have the same response to di erent signals
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