Signal transduction

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 neurotransmitter receptors

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 in cells.

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 in
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 messengers)

TRANSPARENCY (Fig. 11.5) signal molecule -> receptor -> pathway (cascade) ->response

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 a protein)

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 nucleus.

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 and Signal courses, relevant to this topic.

This page was last updated 6/27/02

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