APK 2105C Lecture Notes - Lecture 34: Phosphodiesterase, Caffeine, Endocrine System

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Chapter 5, Lecture 4
Chemical Messengers
Intracellular receptors
o Lipophilic messengers
Bind to nuclear receptor or cytoplasmic receptor
Causes ligand receptor to bind (creates hormone receptor complex) and
moves into nucleus
Hormone response element (specific part of genepromoter sequence)
starts transcription to make mRNA
Can also act to prevent mRNA from formingmore common to
see up-regulation though
mRNA leaves nucleus to start transcription/translation
Membrane-bound receptors
o Channel-linked receptors
Typically see very quick response
Fast ligand-gated channels
These proteins in the membrane act as channels and receptors
Messengers bind to the channels to open them up
o In slow lingand-gated channelsyou can open or close
the channels
Allows ions to move through the channel and change electrical
properties of the cell
o Na is in higher conc outside cell
o K is in higher conc inside cell
Also interact with intracellular proteins for varied responses
o Effects occur quickly
o Binding is brief
o Effects are short-lived
o Ex: bringing in Ca
Higher conc outside cell
Carries 2+--large potential to change electrical
Acting as a 2nd messenger (calmodulin)
Takes messenger from plasma membrane
to initial target cell response
o Enzyme linked receptors
When ligand binds, activates protein
Tyrosine kinases
Add phosphate to tyrosine on a protein
Phosphorylation turns on the protein and gets target cell response
o G protein linked receptors
Regulated by G proteins
3 subunits (alpha beta gamma)
Resting state
o GDP molecule is attached to inactive protein
When molecule comes to the receptor in the cell membrane
o Activates G protein
o G protein loses GDP
o Replaced with GTP molecule
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