1. The Cytoskeleton
Section 4.6

2. Learning Objectives
Contrast the structure & functions of the cytoskeleton with the membrane-bound organelles
Relate the structure of cilia & flagella to their functions

3. Cytoskeleton
Cytoskeleton = system of connected protein filaments inside the cell
Is always changing
Functions include:
Providing strength
Creating cell shape
Allowing cells to move
Filaments include:
Microtubules – the thickest filament
Microfilaments – the thinnest filament
Intermediate filaments – in-between

4. Microtubules Straight, hollow tubes Have the thickest diameter
Made longer by adding pairs of tubulin subunits (dimers)
Easily broken down & reassembled

5. Functions of Microtubules
Provides rigidity & shape in areas of the cell
Holds organelles in place
Acts as tracks or roads for organelles to move around the cell (ex. Vesicles)
Guide the movement of chromosomes during cell division
The main structural component of cilia & flagella

6. Centrosome
Centrosome = area in non-dividing cell where microtubules are organized and anchored
In animal cells it is also the area where centrioles are found

7. Centrioles Organelles found only in animal cells
Barrel-shaped
Perpendicular to each other (90º)
Function is not certain
May play a role in microtubule organization or creation of cilia and flagella

8. Cilia and Flagella
Flagella = long whip-like projections used for movement
Cilia = short hair-like projections used to move liquids and particles across the cell’s surface
Also function in cell signaling

9. Cilia & Flagella Structure
Made of microtubules wrapped in the plasma membrane
9 + 2 Arrangement
Ring of 9 microtubule pairs
Two microtubules in the center of the ring
Connected to a basal body
Has 9 sets of 3 microtubules arranged in a cylinder

10. Motor Proteins
Motor proteins = Proteins that move cell parts when given energy from ATP
Drag cell parts along microtubule & microfilament tracks
Also help to move flagella & cilia
Bend the microtubules to create movement

11. Microfilaments Also called actin filaments
Made of chains of the beadlike protein actin
Looks like a twisted double chain
Are flexible

12. Functions of Microfilaments
Helps support the cell’s shape
Found just inside the plasma membrane
Works with other filaments to make muscle cells contract
Works with myosin filaments
Helps the cell change shape & move
Pseudopodia = “false feet” that help some cells move
Form when microfilaments & microtubules push the plasma membrane outward

14. Intermediate Filaments
Have a ropelike structure
Made of many fibrous proteins wound together
Are the most stable (strongest) filament
Only found in some animal groups

15. Functions of Intermediate Filaments
Reinforce cell shape
Prevent the cell from stretching excessively in response to outside forces
Anchors some organelles so they don’t float around
Ex. The nucleus is held in place by a cage of intermediate filaments