BCH210H1 Lecture Notes - Lecture 18: Integral Membrane Protein, Signal Transduction, Second Messenger System

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BCH210 Lecture 16 signaling
Cellular signaling
- Physiological processes involve biochemical interactions and reactions which allow the
cell to carry out its function
- Cells need to be able to adapt to varying conditions
- The binding of signaling molecules to their receptors initiate processes such as
metabolic pathways and gene expression
- Proteins are needed to carry out this response
Signaling molecules
- Chemical messengers are released by the peripheral or neural cells in response to
stimuli
- Signaling molecules include:
o Small ions
o Sugars
o Hormones
Can act long range (endocrine signaling) or more locally (paracrine /
autocrine) by binding to specific receptors
Lipid soluble hormones include steroids derived from cholesterol
Water soluble hormones are either amino acid derivatives or polypeptides
o Must be kept under control by feedback mechanisms to prevent non-stop
signaling
Signal transduction
- Signal transduction cascades have many components in common:
o Binding specifically to a signal or external messenger in response to a
physiological stimulus
o Reception of the message by the receptor
Usually an integral membrane protein
o Relay of the primary message to the cell interior by the generation of an
intracellular secondary messenger
o Amplification and transduction of the signal
o Response then termination of the signal cascade
G-protein-coupled receptors (GPCRs)
- GPCRs have a primary and secondary structure similar to bacteriorhodopsin as in they
also have 7 TM domains
- They are part of the super-family of membrane proteins
- Can bind various ligands:
o Natural epinephrine, prostaglandins, dopamine
o Synthetic morphine, histamine
- Hormone binding is key for GPCR specificity
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