Chapter 6
Physical Properties of Biomembranes
and Cellular Functions
Abstract Membrane lipids such as phospholipids, glycolipids and sterols form lipid
bilayer membranes spontaneously in water, and insertion and binding of proteins
result in construction of biomembranes. Membrane proteins are surrounded by lipid
molecules, and structure and physical properties of lipid membrane regulate function
and activity of protein through interaction between lipids and proteins. Biological
functions on biomembranes utilize physical property of lipid bilayer membranes.
Molecular collision for chemical reaction is controlled by membrane fluidity which
depends on lipid species of different structures such as length and unsaturation.
Special regions for signaling system on cell membrane are formed by phase separation. Membrane lipid preferring non -bilayer forming is closely related to membrane fusion.
6.1 Diffusion Controlled Process by Fluidity
of Biomembranes
Living organism on the earth is a system of regulated chemical reactions, and
collision of molecules is essential for chemical reaction. And diffusion of molecules
is major factor for collision frequency. Membrane proteins in biomembranes move
in lateral diffusion, and lateral diffusion is measured by such as fluorescence photo
bleaching recovery (FPR) [1].
When chemical reaction A + B ! C is considered, collision theory requires
collision of A molecule and B molecule for chemical reaction of generating product,
C. Collision frequency is proportional to kinetic energy and activation energy
overcoming energy barrier. And proportional coefficient is shown as where k b and
[C] are diffusion-controlled bimolecular constant and concentration of molecule,
C. All collisions not always proceed to generation of product, C. Therefore, rate
constant is shown as k q ¼ γk b where γ is reaction efficiency. And Smolucowski
equation is shown as follows.
k b ¼
9πN A
100 R f þ R q
À
Á
D f þ D q
À
Á
where N A , R f , R q , D f and D r are Avogadro’s
number, radius of colliding and collided molecules, diffusion constant of colliding
© 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_6
81
Physical Properties of Biomembranes
and Cellular Functions
Abstract Membrane lipids such as phospholipids, glycolipids and sterols form lipid
bilayer membranes spontaneously in water, and insertion and binding of proteins
result in construction of biomembranes. Membrane proteins are surrounded by lipid
molecules, and structure and physical properties of lipid membrane regulate function
and activity of protein through interaction between lipids and proteins. Biological
functions on biomembranes utilize physical property of lipid bilayer membranes.
Molecular collision for chemical reaction is controlled by membrane fluidity which
depends on lipid species of different structures such as length and unsaturation.
Special regions for signaling system on cell membrane are formed by phase separation. Membrane lipid preferring non -bilayer forming is closely related to membrane fusion.
6.1 Diffusion Controlled Process by Fluidity
of Biomembranes
Living organism on the earth is a system of regulated chemical reactions, and
collision of molecules is essential for chemical reaction. And diffusion of molecules
is major factor for collision frequency. Membrane proteins in biomembranes move
in lateral diffusion, and lateral diffusion is measured by such as fluorescence photo
bleaching recovery (FPR) [1].
When chemical reaction A + B ! C is considered, collision theory requires
collision of A molecule and B molecule for chemical reaction of generating product,
C. Collision frequency is proportional to kinetic energy and activation energy
overcoming energy barrier. And proportional coefficient is shown as where k b and
[C] are diffusion-controlled bimolecular constant and concentration of molecule,
C. All collisions not always proceed to generation of product, C. Therefore, rate
constant is shown as k q ¼ γk b where γ is reaction efficiency. And Smolucowski
equation is shown as follows.
k b ¼
9πN A
100 R f þ R q
À
Á
D f þ D q
À
Á
where N A , R f , R q , D f and D r are Avogadro’s
number, radius of colliding and collided molecules, diffusion constant of colliding
© 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_6
81