5
C H A P T E R
Cellular Movement
Cellular Movement
and Muscles
and Muscles
Cytoskeleton and Motor Proteins
•
All physiological processes depend on movement
•
Intracellular transport
•
Changes in cell shape
•
Cell motility
•
Animal locomotion
•
All movement is due to the same cellular
“machinery”
•
Cytoskeleton
•
Protein-based intracellular network
•
Motor proteins
•
Enzymes that use energy from ATP to move
Figure 5.1
Use of Cytoskeleton for Movement
Cytoskeleton elements
Microtubules
Microfilaments
Three ways to use the
cytoskeleton for
movement
a.
Cytoskeleton “road” and
motor protein carriers
b.
To reorganize the
cytoskeletal network
c.
Motor proteins pull on the
cytoskeletal “rope”
Microtubules
•
Are tube-like
polymers of
tubulin
•
Similar protein in
diverse animal groups
•
Multiple isoforms
•
Form spontaneously
•
Are anchored at both
ends (polarized)
•
MTOC (–) near the
nucleus
•
Integral proteins (+) in
the plasma membrane
Microtubule Assembly
1.
Monomer activation
2.
Dimer formation (tubulin)
3.
Protofilament formation
4.
Protofilaments
sheet
microtubule
5.
Dimers can be added or
removed from ends of tubule
•
Asymmetrical growth
•
Growth is faster at + end
6.
Cell regulates rates of growth
and shrinkage
Microtubule Growth and Shrinkage
•
Factors affecting
growth/shrinkage are
•
High [tubulin] promotes growth
•
Low temp. promotes shrinkage
•
Microtubule-associated proteins
(MAPs)
•
Dynamic instability
•
GTP hydrolysis on
-tubulin causes
disassembly
•
Chemicals that disrupt the
dynamics
•
For example, plant poisons such as
taxol and colchicine
Treadmilling
Movement Along Microtubules
•
Motor proteins move along
microtubules
•
Direction is determined by
polarity and the type of motor
protein
•
Kinesin
move in (+) direction
•
Dynein
moves in (–) direction
•
Movement is fueled by ATP
hydrolysis
•
Rate determined by the ATPase
domain of motor protein and
regulatory proteins
•
Dynein is larger than kinesin and
moves five times faster
Cilia and Flagella
•
Cilia
•
Numerous, wavelike motion
•
Flagella
•
Single or in pairs, whiplike
movement
•
Composed of microtubules
arranged into axoneme
•
Bundle of parallel
microtubules
•
“Nine-plus-two”
•
Asymmetric activation of
dynein
causes movement
Microfilaments
•
Polymers composed of the protein
actin
•
Found in all eukaryotic cells
•
Often use the motor protein
myosin
•
Movement arises from
•
Actin polymerization (
-actin)
•
Sliding filaments
using myosin (
-actin
)
•
More common than movement by polymerization
Microfilament Structure and Growth
•
G-actin
monomers
polymerize to form a
polymer called
F-actin
•
Energy not required
•
Spontaneous growth
•
6–10 times faster at + end
•
Treadmilling
•
Assembly and disassembly
occur simultaneously and
overall length is constant
•
Capping proteins
•
Increase length by stabilizing
“–” end and slowing
disassembly
Cellular Microfilaments
•
Tangled networks
•
Microfilaments linked by
filamin
protein
•
Bundles
•
Cross-linked by
fascin
protein
•
Networks and bundles of microfilaments are attached to cell
membrane by
dystrophin
protein
•
Maintain cell shape and can be used for movement
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- Winter '19
- Physiology, Proteins
