Structure and Properties of Cell Membrane Structure and Properties of Cell Membranes

Volume II

Gheorghe Benga

• Publisher: CRC Press
• Year: 2018
• ISBN:
  9781351093873
• Edition: 1
• Topic: Scienze biologiche
• Subtopic: Biologia cellulare

This book provides in-depth presentations in membrane biology by specialists of international repute. The volumes examine world literature on recent advances in understanding the molecular struc-ture and properties of membranes, the role they play in cellular physiology and cell-cell interactions, and the alterations leading to abnormal cells. Illustrations, tables, and useful appendices com-plement the text. Those professionals actively working in the field of cell membrane investigations as well as biologists, biochemists, biophysicists, physicians, and academicians, will find this work beneficial.

Chapter 1

BASIC KINETICS OF MEMBRANE TRANSPORT

Arnošt Kotyk

TABLE OF CONTENTS

I. Introduction

II. Nonspecific Permeation

III. Specific Transport

A. Specific Channels or Pores

B. Specific Carriers

References

I. INTRODUCTION

In this chapter, we shall deal with the rates of movement of substances across membranes during their transport or translocation. At the outset, let us accept some restrictions and simplifications for the purposes of this treatment, as they are common throughout transport literature.

1. The membrane is “infinitely” thin so that no intramembrane gradients are to be considered.

2. The solutions separated by the membrane are sufficiently mixed so that there is a unique concentration of solute at any time in each of them.

3. The transport system resides in the membrane and cannot leave it so that its “concentration” in the membrane does not change during the experiment.

Two fundamentally different mechanisms of membrane transport exist: nonspecific permeation (often called simple diffusion) and specific, saturable transport (often termed carrier or porter transport).

II. NONSPECIFIC PERMEATION

In the first type of transmembrane movement, no specific reactions take place between the permeant solute and the permeable membrane, although nonspecific interactions, such as stripping of hydration water, attraction by opposite electrical charges, and the like, are possible and, in fact, likely.

The rate of such transport (in kmol s⁻¹ m⁻²) is defined from Fick’s First Law of diffusion for movement along one of the coordinates

${\text{J}}_{\text{S}}=-\text{D}({\text{S}}_{\text{II}}-{\text{S}}_{\text{I}})/\text{δ}=\text{P}({\text{S}}_{\text{I}}-{\text{S}}_{\text{I}\text{I}})$

(1)

where S_I and S_II are solute concentrations (kmol m⁻³) at the starting and at the target sides of the membrane, respectively, D is the diffusion coefficient across the membrane in m²s⁻¹, δ the membrane thickness in m, and P the permeability constant in m s⁻¹.

D itself may be defined as RTU where R is the gas constant (8.314 J mol⁻¹ K⁻¹), T the absolute temperature (in K), and U the mobility (in m² s⁻¹ J⁻¹ mol). This suggests that diffusion processes have a poorly expressed temperature dependence, something like 3% increase in D per 10°C rise in the physiological temperature range. This is, however, not true for transmembrane crossing. We must consider here a different definition of P, which must be taken as phenomenological, only as it holds both for passage through membrane lipid domains as well as for movement through hydrophilic channels. It states that

$\text{P}=\text{K}{\text{D}}_{\text{m}}/\text{δ}$

(2)

where D_m is the diffusion coefficient of the solute within the membrane and K the partition coefficient between the membrane and the exterior aqueous solution. It i...

Table of contents

• Cover
• Title Page
• Copyright Page
• Table of Contents
• Chapter 1 Basic Kinetics of Membrane Transport
• Chapter 2 pH Effects on Membrane Transport
• Chapter 3 The Effect of Membrane Lipids on Permeability and Transport in Prokaryotes
• Chapter 4 The Influence of Membrane Lipids on the Permeability of Membranes to Ca2+
• Chapter 5 Molecular Aspects of Structure-Function Relationship in Mitochondrial H+-ATPase
• Chapter 6 Molecular Aspects of the Structure-Function Relationship in Cytochrome c Oxidase
• Chapter 7 Molecular Aspects of Structure-Function Relationships in Mitochondrial Adenine Nucleotide Carrier
• Chapter 8 Exocytosis, Endocytosis, and Recycling of Membranes
• Chapter 9 The Surface Potential of Membranes: Its Effect on Membrane-Bound Enzymes andTransport Processes
• Index