The Cytoskeleton Section 4.6

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

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

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

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

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

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

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

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

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

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

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

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

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