116A WEEK 8 – Cytoskeleton and Motility
Learning outcomes:
1. Define the cytoskeleton and its functions
2. Describe the structural elements of the cytoskeleton: cytoskeletal
filaments and motors
3. Explain how the cytoskeleton is regulated
4. Describe the microtubule- and actin-based systems for cell motility
5. Describe cell migration and its types
Prelecture notes:
- The cytoskeleton consists of three main components:
o Actin filaments: Thinnest, involved in muscle contraction, cell
movement, and division. Forms networks that allow cells to
change shape and move
o Microtubules: Thickest, responsible for intracellular transport,
structural support, and cell division. Forms tracks for vesicle
movement and aid in chromosome separation during cell
division. Microtubules also support structures like flagella and
cilia for cell movement
o Intermediate filaments: Provides mechanical strength and
stability. These rope-like structures anchor organelles and cells
to their surroundings, and their types vary across cell types,
including keratins in skin and hair, vimentin in muscle cells,
and lamins around the nucleus.
What is the cytoskeleton?
- A network of interconnected filaments
- Polymers (provide structure)
- Dynamic (direct rearrangement)
Function:
- Cell structure and mechanics
- Force generation – motility
- Intracellular transport
- Cell division
Why is it important?
- Keeps the cell shape, rearranges contents
- Cell division, migration, motility, intracellular transport
- Force generation and sensing
- Dysregulation leads to pathological conditions (invasive cancer etc)
Types of cytoskeletal filaments
Actin filaments Microtubules Intermediate filaments
Diameter/ 7nm/36nm 25nm/4nm ~10nm/various
repeat length
Monomer Actin Tubulin ( & Lamin/desmin/vimentin/
tubulin) keratin etc
, Polar? Ends Yes Yes No
are different
Functions Muscle Mitotic spindle Cell shape/stiffness
contraction Intracellular Nuclear lamina
Cell motility trafficking of
(crawling) organelles
Cytokinesis Microtubule-based
Cell shape structures (cilia,
centrosomes,
axonemes)
Types of cytoskeletal filaments and motors:
- Actin filaments (microfilaments) myosin
- Microtubules kinesin, dynein
- Intermediate filaments doesn’t have any known motors
Molecular motors
- Consumes ATP
- Makes steps along the filaments
- Transports cargo, rearranges membranes and
cytoskeletal networks
Mechano-chemical cycle of kinesin
stepping
- 1. ADP: strongly bound state
- 2. ATP: power stroke
- 3. ADP.Pi: Release
- One step = 8nm (one tubulin
dimer)
Cytoplasmic and axonemal dynein
- Cytoplasmic dynein: movement of cargos
along microtubules, cell division
- Axonemal dynein: beating of cilia and flagella
Learning outcomes:
1. Define the cytoskeleton and its functions
2. Describe the structural elements of the cytoskeleton: cytoskeletal
filaments and motors
3. Explain how the cytoskeleton is regulated
4. Describe the microtubule- and actin-based systems for cell motility
5. Describe cell migration and its types
Prelecture notes:
- The cytoskeleton consists of three main components:
o Actin filaments: Thinnest, involved in muscle contraction, cell
movement, and division. Forms networks that allow cells to
change shape and move
o Microtubules: Thickest, responsible for intracellular transport,
structural support, and cell division. Forms tracks for vesicle
movement and aid in chromosome separation during cell
division. Microtubules also support structures like flagella and
cilia for cell movement
o Intermediate filaments: Provides mechanical strength and
stability. These rope-like structures anchor organelles and cells
to their surroundings, and their types vary across cell types,
including keratins in skin and hair, vimentin in muscle cells,
and lamins around the nucleus.
What is the cytoskeleton?
- A network of interconnected filaments
- Polymers (provide structure)
- Dynamic (direct rearrangement)
Function:
- Cell structure and mechanics
- Force generation – motility
- Intracellular transport
- Cell division
Why is it important?
- Keeps the cell shape, rearranges contents
- Cell division, migration, motility, intracellular transport
- Force generation and sensing
- Dysregulation leads to pathological conditions (invasive cancer etc)
Types of cytoskeletal filaments
Actin filaments Microtubules Intermediate filaments
Diameter/ 7nm/36nm 25nm/4nm ~10nm/various
repeat length
Monomer Actin Tubulin ( & Lamin/desmin/vimentin/
tubulin) keratin etc
, Polar? Ends Yes Yes No
are different
Functions Muscle Mitotic spindle Cell shape/stiffness
contraction Intracellular Nuclear lamina
Cell motility trafficking of
(crawling) organelles
Cytokinesis Microtubule-based
Cell shape structures (cilia,
centrosomes,
axonemes)
Types of cytoskeletal filaments and motors:
- Actin filaments (microfilaments) myosin
- Microtubules kinesin, dynein
- Intermediate filaments doesn’t have any known motors
Molecular motors
- Consumes ATP
- Makes steps along the filaments
- Transports cargo, rearranges membranes and
cytoskeletal networks
Mechano-chemical cycle of kinesin
stepping
- 1. ADP: strongly bound state
- 2. ATP: power stroke
- 3. ADP.Pi: Release
- One step = 8nm (one tubulin
dimer)
Cytoplasmic and axonemal dynein
- Cytoplasmic dynein: movement of cargos
along microtubules, cell division
- Axonemal dynein: beating of cilia and flagella
