01:694:301 Lecture Notes - Lecture 14: Signal Transduction, Adrenergic Receptor, Cyclic Adenosine Monophosphate
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14 Nov 2018
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Chapter 14 – ‘Signal-Transduction Pathways’
Different Types of Signaling in STPs
• Ch.14 is full of fascinating material about signal transduction, which is one of the most
interesting areas of biochemistry.
o When a cell receives a message that this is X molecule in its env. above threshold [], chain
of events converts this message to the ultimate physiological response
• You should understand the discussion of 7TM receptors (e.g. β-adrenergic) and G-proteins
(404-5) which leads to discussion of cyclic amp (cAMP)
o 7TM receptors (
7 transmembrane helix
) – largest class of cell-surface receptors; signal
through G-proteins; also referred to as
G-protein coupled receptors
(GPCRs)
! Contain 7 helices that span membrane bilayer; snakes through membrane 7x
! Binding of ligand outside cell causes conformational change in 7TM receptor inside
the cells
! Ex:
rhodopsin
– found in retina; senses photons and initiates signals for visual
sensation
! Epinephrine signaling begins with ligand binding to a protein called the β
-adrenergic
receptor
• Epinephrine is hormone secreted by adrenal glands in respond to external or
internal stressors
! β
-adrenergic receptor
and
rhodopsin
have similarities structurally;
• Similar location found b/w rhodopsin " 11-cis-retinal; β
-adrenergic receptor
inhibitor carazolol
o G-proteins activated by ligand binding of 7TM receptors
! In inactivated state, G-proteins bound to GDP; in this form it exists as a heterotrimer
consisting of α,β, and γ subunits