Charged Membranes

Sci. Signal., 16 April 2013
Vol. 6, Issue 271, p. tr6
DOI: 10.1126/scisignal.2003454

Charged Membranes

  1. Jack D. Thatcher*
  1. West Virginia School of Osteopathic Medicine, 400 North Lee Street, Lewisburg, WV 24901, USA.
  1. *Corresponding author. E-mail: jthatcher{at}osteo.wvsom.edu

Abstract

This Teaching Resource provides three animated lessons that describe the storage and utilization of energy across plasma membranes. The “Na,K ATPase” animation explains how these pumps establish the electrochemical gradient that stores energy across plasma membranes. The “ATP synthesizing complexes” animation shows how these complexes transfer energy from the inner mitochondrial membrane to adenosine triphosphate (ATP). The “action potential” lesson explains how charged membranes are used to propagate signals along the axons of neurons. These animations serve as valuable resources for any collegiate-level course that describes these important factors. Courses that might employ them include introductory biology, biochemistry, biophysics, cell biology, pharmacology, and physiology.

Description

These animated lessons describe mechanisms for establishing and using charged membranes (1). The animations serve as valuable resources for any collegiate-level course that describes these processes (2). Courses that might employ them include introductory biology, biochemistry, biophysics, cell biology, pharmacology, and physiology.

The “Na,K ATPase” lesson explains how an electrochemical gradient is established to store energy across charged membranes (Fig. 1) (3). It shows how the Na+- and K+-dependent adenosine triphosphatase (Na+/K+-ATPase) pumps more sodium (Na+) ions out of the cell than potassium (K+) ions into the cell. It then shows how the resulting excess of cations on the extracellular face of the membrane attracts anions to the intracellular face. Finally, it shows how separate K+ channels amplify the electric potential.

Fig. 1

A static image from the “Na,K ATPase” animation showing how this pump functions to store energy across charged membranes. View animation at http://stke.sciencemag.org/cgi/content/full/6/271/tr6/DC1.

The lesson called “ATP synthesizing complexes” (Fig. 2) explains how this complex, which is embedded in the inner mitochondrial membrane, functions by displaying it at multiple angles (4). Hydrogen (H+) ions flow through the transmembrane turbine Fo domain to turn the turbine. Energy from the turbine is transduced through the complex to drive ATP synthesis by the F1 ATPase domain inside the mitochondrial matrix.

Fig. 2

A static image from the “ATP synthesizing complexes” animation showing how this complex transfers energy from a charged membrane to the triphosphate bond of ATP. View animation at http://stke.sciencemag.org/cgi/content/full/6/271/tr6/DC1.

The “action potential” lesson depicts neural conduction by displaying graphs in parallel with animated images (Fig. 3). Depolarization of the membrane occurs when voltage-gated Na+ channels open in response to changes in electric potential, which increases Na+ permeability and allows Na+ to flow into the axon and thus elevates the membrane potential. Repolarization occurs approximately half a millisecond later, when Na+ channels spontaneously close and voltage-gated K+ channels open. Na+ permeability decreases, K+ permeability increases, K+ diffuses down its electrochemical gradient out of the cell, and the membrane potential drops below resting potential. The resting potential of the membrane is then restored by Na+/K+-ATPases.

Fig. 3

A static image from the “action potential” animation showing how energy from the charged membrane is used to propagate neuronal signal. View animation at http://stke.sciencemag.org/cgi/content/full/6/271/tr6/DC1.

Two modes are provided for each lesson, “labeled” and “pop-up.” Users can toggle between the modes at any point in a lesson. In the “labeled” mode, titles, labels, and explanatory text accompany the images. The explanatory text makes an animation useful for self-study. To make an animation appropriate as a visual aid for lectures, the explanatory text can be toggled off, which prevents it from competing with an instructor’s verbal explanations. The “pop-up” mode is designed to summarize key points, which makes it particularly conducive to self-study. Information appears when the cursor is passed over an object. In many cases, additional information appears when the object is clicked.

Educational Details

Learning Resource Type: Animation, diagram

Context: Undergraduate lower division, undergraduate upper division

Intended Users: Teacher, learner

Intended Educational Use: Learn, teach

Discipline: Biochemistry, cell biology, physiology, biophysics

Keywords: Action potential, ATP synthesizing complexes, depolarization, electrochemical gradient, Fo domain, F1 domain, K+ channel, Na+/K+-ATPase, repolarization, resting potential, voltage-gated K+ channel, voltage-gated Na+ channel

Technical Details

Format: FLASH animation

Size: 82 kb (Na,K ATPase.swf), 150 kb (Action Potential.swf), 465 kb (ATP Synthesizing Complexes.swf)

Requirements: Flash-enabled Web browser

Supplementary Materials

(http://stke.sciencemag.org/cgi/content/full/6/271/tr6/DC1)

Animation 1. Na,K ATPase

Animation 2. ATP synthesizing complexes

Animation 3. Action potential

References

Citation:

J. D. Thatcher, Charged Membranes. Sci. Signal. 6, tr6 (2013).
Science Signaling. ISSN 1937-9145 (online), 1945-0877 (print). Pre-2008: Science's STKE. ISSN 1525-8882