Campbell and Reece, Chapter 11
The plasmalemma (cell membrane) makes a barrier. Already, we covered how
specific molecules (channels) can make membrane permeable to ions. That
allows electrical excitability. Now we cover other widespread ways to get
signals across the membrane.
TRANSPARENCY (Fig. 11.3) there are several kinds of ways to get signals
around the body, the most famous of which are synapses from one nerve cell
to another (or to another kind of cell) and hormones. Endocrine glands (as
opposed to exocrine glands that have ducts like those involved in digestive
secretions) secrete into the blood stream. Although the figure implies that
the hormone goes into the cell, as is the case with steroids (lipids that
can cross the hydrophobic membrane) this chapter covers membrane receptors.
TRANSPARENCY (Fig. 11.9) some receptors are channels, including many famous
The 1991 Nobel Prize
in Physiology and Medicine was awarded jointly to ERWIN NEHER and BERT
SAKMANN for their discoveries concerning the function of single ion channels
The 1963 Nobel Prize
in Physiology and Medicine was was awarded jointly to: SIR JOHN CAREW
ECCLES , SIR ALAN LLOYD HODGKIN and SIR ANDREW FIELDING HUXLEY for their
discoveries concerning the ionic mechanisms involved in excitation and inhibition
the peripheral and central portions of the nerve cell membrane.
TRANSPARENCY (Fig. 11.12) ATP ->(adenylyl cyclase)-> cAMP (cyclic,
second messenger) plus pyrophosphate ->(phosphodiesterase)-> AMP
The 1971 Nobel Prize
in Physiology and Medicine went to EARL W. JR. SUTHERLAND for his discoveries
concerning the mechanisms of the action of hormones (the discovery of second
TRANSPARENCY (Fig. 11.5) signal molecule -> receptor -> pathway (cascade)
TRANSPARENCY (Fig. 11.6) one of the most famous receptors is a protein with
7 membrane-spanning alpha helices, the G-protein coupled receptor, examples
being rhodopsin (the molecule of visual transduction), and various hormone
and transmitter receptors.
TRANSPARENCY (Fig. 11.7) G-protein is activated by binding GTP, inactivated
as GTPase activity converts GTP to GDP + Phosphate. (note that an enzyme
is later in the cascade)
The 1994 Nobel Prize
in Physiology and Medicine was awarded jointly to: ALFRED G. GILMAN
and MARTIN RODBELL for their discovery of G-proteins and the role of these
proteins in signal transduction in cells.
TRANSPARENCY (Fig. 11.13) An example of a G-protein cascade using epinephrine
(adrenalin) and utilizing cAMP to activate PKA (a kinase phosphorylates
TRANSPARENCY (Fig. 11.15) Some G-protein cascades make second messengers
(IP3 and DAG) from the membrane lipid PIP2, note that calcium ion becomes
a third messenger. The right side of this diagram implies that one type
of cell may have sever interacting signal mechanisms. Also note that the
"cellular responses) seem to be going on in the cytoplasm in this example.
TRANSPARENCY (Fig. 11.8) Some receptor molecules are themselves enzymes
such as this receptor tyrosine kinase (a receptor that is an enzyme that
phosphorylates the protein on the tyrosine amino acid).
TRANSPARENCY (Fig. 11.10) Ultimately many signals change the transcription
of certain genes, and steroid hormones are a model for this. Notably, they
go through the membrane, and the receptor is in the cytoplasm and/or the
TRANSPARENCY (Fig. 11.17) Importantly, many signal transduction cascades,
especially those involved in development, affect which genes are active
via transcription factors. Remember, different cells have the same genes
of the whole genome but have different subsets of these genes expressed.
Note that I offer Neuro
courses, relevant to this topic.
This page was last updated 6/27/02
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