BIOC 2300 Lecture Notes - Lecture 14: Signal Transduction, Protein Kinase A, G Protein–Coupled Receptor
3 May 2018
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Signal Transduction
February 10th, 2016
*See overview of signal transduction
• Extracellular signal molecules binds to cell-surface receptor protein
• Creates an intracellular signalling pathway (FAST)
• Altered protein synthesis is a slow mechanisms
Overview of Signal transduction
• Can be classified in several ways due to nature/origin of signal, type of receptor and
physiological system:
o Contact dependent
o Paracrine
o Synaptic – rapid signalling in nervous system at synapse
o Endocrine
• Five important themes:
o Ligands bind to specific receptors
o Signals are propagated by transient second messengers
o Protein phosphorylation amplifies signalling cascades
o G-proteins act as molecular switches
o Modular domains enhance signal efficiency and regulation
Extracellular Signals (Ligands) can be any type of molecules
• Do not need to memorize different types
• Steroid hormones and gases do not need a receptor to enter membrane
Receptor-Ligand Binding
• Except for membrane permeable signals, most extracellular signals must bind to
membrane receptors to initiate signalling
• An agonist is a ligand that initiates a biological response, while an antagonist binds to the
receptor but causes no response
• Simple receptors, exhibit saturation behaviour with a constant Kd
o Kd = [R][L]/[R*L]
• Kd is the [ligand] when receptor is half saturated
o Low values high affinity
• The result is usually a conformational change to activate receptor
Two Major Receptor Types: GPCR and RTK
• GPCR
o Uses G protein coupled receptor
o When ligand binds, G protein is active which the binds to an ezyme to produce
second messengers to target proteins
• RTK
o Recptor tyrosine kinase
o Binding causes ATPADP
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