APK 2105C Lecture Notes - Lecture 34: Phosphodiesterase, Caffeine, Endocrine System
5 Jun 2018
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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 gene—promoter sequence)
starts transcription to make mRNA
• Can also act to prevent mRNA from forming—more 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 channels—you 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
potential
▪ 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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