Cytoskelton and Cell Motility

PRESENTED BY:

RAMANDEEP KAUR

ASSTT. PROF. IN BOTANY

Cytoskeleton

• Means “cell skeleton”
• Internal framework of cell
• Has many functions
• Anchoring cell organelles
• Provide cell shape
• Aids in cell motility
• Response to environmental signals
• Comprises
• Microtubules
• Microfilaments
• Intermediate filaments

Microtubules

• Hollow tubes made of the protein tubulin
• Alternating dimers of α and β tubulin
• Largest of cytoskeleton filaments
• Is used for:
• Maintenance of cell shape
• Motility
• Flagella or cilia
• Movement of organelles through cell
• Often involves motor molecule
• Often originate from centrosome

10 µm

Column of tubulin dimers

Tubulin dimer

α

β

25 nm

Centrioles

• Located in centrosome of animal cells
• Occur in perpedicular pair
• Have 9 triplets of microtubules
• Facilitate microtubule assembly and chromosome separation in some cells

Centrosome

Microtubule

Centrioles

0.25 µm

Longitudinal section of one centriole

Microtubules

Cross section

of the other centriole

Flagellum structure

• Basal body links flagellum or cilia to cell surface
• Basal body looks just like a centriole
• 9 +2 arrangement of microtubules
• Radial spokes prevent dramatic sliding and only bending

​

0.1 µm

Triplet

(c) Cross section of basal body

(a)

Longitudinal section of cilium

0.5 µm

Plasma membrane

Basal body

Microtubules

(b)

Cross section of cilium

Plasma membrane

Outer microtubule doublet

Dynein proteins

Central microtubule

Radial spoke

Protein cross-linking outer doublets

0.1 µm

Motor molecules

• Interact with tubulin or actin
• Are fixed at one end and allowed to move freely at the other end
• Movement is directional
• Undulation-used for flagella and cilia movement
• Two microtubules moving relative to one another
• Organelle movement is like a ski lift tram or a monorail

Vesicle

ATP

Receptor for motor protein

Microtubule

of cytoskeleton

Motor protein (ATP powered)

(a)

Microtubule

Vesicles

(b)

0.25 µm

Cell motility

• Cell movement facilitated by flagella or cilia
• Unlike in prokaryotes, eukaryotic flagella undulate
• Cilia are small appendages and they move like a swimmers arm-active stroke and return stroke

How cell movement works

• Dynein is motor molecule that interacts with tubulin
• Dynein walks along one microtubule, while bound to another
• This results in bending
• If no radial spokes or organelle coat, then microtubules would walk out of cell

Microtubule

doublets

Dynein

protein

ATP

ATP

(a) Effect of unrestrained dynein movement

Cross-linking proteins

inside outer doublets

Anchorage

in cell

(b) Effect of cross-linking proteins

1

3

2

(c) Wavelike motion

Microfilaments

• Made of two intertwined strands of actin
• Helps maintain cell shape
• Actin rearrangements allow engulfment events
• Psuedopod formation in ameoba
• Promote cytoplasmic streaming in plants
• Essential for muscle contraction
• Used by invading bacteria to move around cell
• Frequently being assembled and disassembled within cell

Actin subunit

10 µm

7 nm

Microfilaments 2

• Myosin interacts with actin to cause contraction
• Cytoplasmic streaming and ameoboid motion are similar
• Cortical cytoplasm around the perimiter of cell contains perpendicular actin (wind fence)
• Streaming portion has parallel actin which facilitates cytoplasm movement
• Plant cell wall prevents amoeboid movement of plant cell

​

Intermediate Filaments

• Resemble cable in structure
• Are made of protein subunits
• Help maintain cell shape
• Are durable and not assembled and disassembled as other cytoskeleton components
• May help maintain organelle position

5 µm

Keratin proteins

Fibrous subunit (keratins

coiled together)

8–12 nm