Chapter 7
Moving Life
Abstract Previous chapters have dealt with the phenomenon centered on the
structure and function of biological membranes. The lipid membrane is an essential
structure that guarantees the steady state of the life in the ever-changing environment. Non-stop exchange of matters and information with the environment is a
salient feature of the activity of living thing. The previous chapters describe various
facts of these aspects. Voluntary movement is another remarkable feature of living
things. Thus in Chap. 7, various types of biological motions are described. First,
muscle contraction is briefly described, because it is one of the best known and
studied example of the motor-based biological motions. Another well-studied example of the motor-based motion is the organelle transport; microscopic observations
and analysis of the motion are described as examples. Motors related to the transport
motility are briefly described and actin and microtubule tracks are described in some
detail. The dynamism of the cell is largely depends on the dynamism of the system of
actin filaments, microtubules and intermediate filaments. These filament systems are
assembled or disassembled according to the needs of the cell, which is adopted in
generating cellular movements. In the case of actin filaments and microtubules the
movements such as lamellipodial protrusion, segregation of chromosomes and
organelle transport, are driven. For these phenomena polymerization and depolymerization of the subunit of these polymers play essential roles. Thus, the
polymerization/depolymerization-driven motions in the cell are one of the main
theme of the last half of this chapter.
First, structure of actin monomer and tubulin, actin filament and microtubule are
described, and kinetics of polymerization of actin is then explained, because it is
necessary to understand the polymerization/depolymerization-driven motions in the
cell. Following these sections, overview of the cell motility is given, which is
followed by explanation on the actin-related structures in the cell. An important
question on the actin-based motility is that if it can really develop the force that leads
to the mechanical work such as deformation of the cell membranes in lamellipodial
protrusion. Three examples are presented: (1) the measurements done on two types
of cells keratocyte, a highly motile cell, and a fibroblast, rather quiescent cell; (2) the
reconstituted systems, liposomes encapsulating actin or monomeric unit of microtubule (tubulin); (3) actin-based movement of bacteria. Then, theories that were
© 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_7
95
Moving Life
Abstract Previous chapters have dealt with the phenomenon centered on the
structure and function of biological membranes. The lipid membrane is an essential
structure that guarantees the steady state of the life in the ever-changing environment. Non-stop exchange of matters and information with the environment is a
salient feature of the activity of living thing. The previous chapters describe various
facts of these aspects. Voluntary movement is another remarkable feature of living
things. Thus in Chap. 7, various types of biological motions are described. First,
muscle contraction is briefly described, because it is one of the best known and
studied example of the motor-based biological motions. Another well-studied example of the motor-based motion is the organelle transport; microscopic observations
and analysis of the motion are described as examples. Motors related to the transport
motility are briefly described and actin and microtubule tracks are described in some
detail. The dynamism of the cell is largely depends on the dynamism of the system of
actin filaments, microtubules and intermediate filaments. These filament systems are
assembled or disassembled according to the needs of the cell, which is adopted in
generating cellular movements. In the case of actin filaments and microtubules the
movements such as lamellipodial protrusion, segregation of chromosomes and
organelle transport, are driven. For these phenomena polymerization and depolymerization of the subunit of these polymers play essential roles. Thus, the
polymerization/depolymerization-driven motions in the cell are one of the main
theme of the last half of this chapter.
First, structure of actin monomer and tubulin, actin filament and microtubule are
described, and kinetics of polymerization of actin is then explained, because it is
necessary to understand the polymerization/depolymerization-driven motions in the
cell. Following these sections, overview of the cell motility is given, which is
followed by explanation on the actin-related structures in the cell. An important
question on the actin-based motility is that if it can really develop the force that leads
to the mechanical work such as deformation of the cell membranes in lamellipodial
protrusion. Three examples are presented: (1) the measurements done on two types
of cells keratocyte, a highly motile cell, and a fibroblast, rather quiescent cell; (2) the
reconstituted systems, liposomes encapsulating actin or monomeric unit of microtubule (tubulin); (3) actin-based movement of bacteria. Then, theories that were
© 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_7
95