Chapter 4
Structure and Physical Properties
of Biomembranes
Abstract Biological functions of biomembranes are closely related to their structures and physical properties because most of membrane functions require lipid
bilayer membranes. The lipid bilayer membranes are composed of a lot of number of
lipid molecules, proteins and other constituents. These molecules make statistical
assembly and show phase transition and phase separation. And change of these
physical properties including membrane fluidity affect and regulate biological functions of biomembranes.
4.1 Structure of Biomembranes
Cell is an essential unit of life and composed of various biomembranes. Major
components of the biomembranes are proteins and lipids. These components were
obtained in early study of cells, but structure of the biomembranes was not elucidated long time. Some models of biomembranes were proposed before fluid mosaic
model proposed by Singer and Nicolson. The model has shown basic concept of
biomembranes which is widely accepted as a standard model of biomembranes [1]
(Fig. 4.1). They used preceding studies related to membrane structure in addition to
their own freeze- fractured study of red blood cell membranes. The preceding studies
are calculation of free energy in theory of hydrophobic effect [2], phase transition of
cell membrane and extracted lipids measured by DSC, which shows lipid molecules
form statistical assembly in cell membranes [3]. X- ray diffraction pattern of neuron
membranes showed structure with 40 angstroms thickness [4]. Axial rotation [5] and
flip-flop [6] of lipid spin probes in lipid bilayer membranes were observed by ESR.
Using fluorescence antibody and cell fusion by Sendai virus, lateral diffusion of
histocompatibility antigens on cell membranes was observed by fluorescence microscope [7]. There are other studies using freeze-fractured electron microscopy [8, 9]
and particles in the fractured surface of biomembrane were proved to be proteins
[10]. Two types of membrane proteins were introduced in the fluid mosaic membrane model. One is peripheral protein which is defined as protein released from cell
membrane by treatment with chelating reagent and increasing ionic intensity because
© Springer Japan KK, part of Springer Nature 2018
K. Ohki, H. Miyata, Physical Principles of Biomembranes and Cells,
Biological and Medical Physics, Biomedical Engineering,
https://doi.org/10.1007/978-4-431-56841-4_4
59
Structure and Physical Properties
of Biomembranes
Abstract Biological functions of biomembranes are closely related to their structures and physical properties because most of membrane functions require lipid
bilayer membranes. The lipid bilayer membranes are composed of a lot of number of
lipid molecules, proteins and other constituents. These molecules make statistical
assembly and show phase transition and phase separation. And change of these
physical properties including membrane fluidity affect and regulate biological functions of biomembranes.
4.1 Structure of Biomembranes
Cell is an essential unit of life and composed of various biomembranes. Major
components of the biomembranes are proteins and lipids. These components were
obtained in early study of cells, but structure of the biomembranes was not elucidated long time. Some models of biomembranes were proposed before fluid mosaic
model proposed by Singer and Nicolson. The model has shown basic concept of
biomembranes which is widely accepted as a standard model of biomembranes [1]
(Fig. 4.1). They used preceding studies related to membrane structure in addition to
their own freeze- fractured study of red blood cell membranes. The preceding studies
are calculation of free energy in theory of hydrophobic effect [2], phase transition of
cell membrane and extracted lipids measured by DSC, which shows lipid molecules
form statistical assembly in cell membranes [3]. X- ray diffraction pattern of neuron
membranes showed structure with 40 angstroms thickness [4]. Axial rotation [5] and
flip-flop [6] of lipid spin probes in lipid bilayer membranes were observed by ESR.
Using fluorescence antibody and cell fusion by Sendai virus, lateral diffusion of
histocompatibility antigens on cell membranes was observed by fluorescence microscope [7]. There are other studies using freeze-fractured electron microscopy [8, 9]
and particles in the fractured surface of biomembrane were proved to be proteins
[10]. Two types of membrane proteins were introduced in the fluid mosaic membrane model. One is peripheral protein which is defined as protein released from cell
membrane by treatment with chelating reagent and increasing ionic intensity because
© Springer Japan KK, part of Springer Nature 2018
K. Ohki, H. Miyata, Physical Principles of Biomembranes and Cells,
Biological and Medical Physics, Biomedical Engineering,
https://doi.org/10.1007/978-4-431-56841-4_4
59