Biochemistry Online: An Approach Based on Chemical Logic

CHAPTER 9 - SIGNAL TRANSDUCTION

B: NEURAL SIGNALING

BIOCHEMISTRY - DR. JAKUBOWSKI

06/10/14

Learning Goals/Objectives for Chapter 9B:
After class and this reading, students will be able to

describe how a transmembrane ion gradient and nongated/gated membrane ion channels specific for given ions can give rise to a transmembrane electric potential across membranes
given ion concentrations and the electrical potential across a membrane, predict likely changes in the membrane potential and ion concentrations on the opening of specific channnels;
use the Goldman equation to predict transmembrane electrical potentials;
state difference between the communication across the neuromuscular junction and a synapse between two neurons;
state the difference between nongated and gated ion channels;
describe different ways to open/close gated ion channels
describe the immediate changes in the muscle cells when acetylcholine is released into the neuromuscular junction
describe the roles of stimulatory neurotransmitter receptors, voltage-gated Na+and K+ channels and the Na/K-ATPase in the activation of a neuron;
explain the mechanism for selectivity of K+ over the smaller Na+ ion in the K+ channel;
briefly explain how membrane protein channels can be gated open by changes in transmembrane potential;

B13. Summary

1. the same ions moving through different channels can have different consequences. Consider the example of potassium ions. When it moves through a:

nongated channel, it establishes the resting potential
a voltage gated channel, it repolarizes the cell after an action potential
channel that is gated by chemical modification (such as phosphorylation), it may hyperpolarize the membrane (make it more negative inside) and facilitate neuron inhibition

2. If two ions are involved in signaling, the result depends on

if the two species move simultaneously through the same channel (which results in excitation through an initial depolarization of membrane if the ions are potassium and sodium)
if the two species move through different channels in a sequential fashion (which generates an action potential) if the ions are potassium and sodium).

In summary, ligand and voltage gated channels allow changes in the polarization of the membrane. Other mechanisms can also lead to changes. Membrane proteins can be phosphorylated (using ATP) by protein kinases in the cell, leading to a change in the conformation of the membrane protein, and either an opening or closing of the channel. Channels linked to the cytoskeleton of the cells can also be opened or closed through stretching. Other stimuli that gate channels are light (through photoisomerization-induced conformational changes), heat, and cold.

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