The Cytoskeleton and Cell Surfaces

Microfilaments

Also called actin filaments. Solid rods composed mainly of globular proteins called actin, arranged in a twisted double chain.

Cilia and Flagella

Cilia and flagella are composed of microtubules wrapped in an extension of the plasma membrane. The short, numerous appendages that propel Paramecium are called cilia. Other protists may move when using flagella, which are longer than cilia and usually limited to one or a few per cell. Ex. Sperm

Centrosome

Contains a pair of centrioles, each composed of a ring of microtubules. Plant cells lack centrosomes with centrioles and organize microtubules by other means.

Function of Microfilaments

Form a 3-D network just inside the plasma membrane that helps support the cell's shape. Involved in cell movements. Actin filaments and thicker filaments made of a type of motor protein called myosin interact to cause contraction of muscle cells. The contractions are involved in the amoeboid (crawling) movement of the protist Amoeba and some of your white blood cells.

Intermediate Filaments

Found in the cells of most animals. Made of various fibrous proteins that supercoil into cables.

Function of a Microtubule

Microtubules shape and support the cell and also act as tracks along which organelles equipped with motor proteins move. Example: A lysosome might use its "feet" to "walk" along a microtubule to reach a food vacuole. Microtubules also guide the movement of chromosomes when cells divide. They are the main components of cilia and flagella.

Cytoskeleton

Networks of protein fibers that extend throughout a cell. The fibers act like a skeleton in providing for structural support as well as movement. Made up of three main fibers: micro-tubules, micro-filaments, and intermediate filaments.

Function of Intermediate Filaments

Reinforce cell shape and anchor some organelles. Example: The nucleus typically sits in a cage made of intermediate filaments.

Microtubules

The thickest fiber that makes up the cytoskeleton. Straight, hollow tubes composed of globular proteins called tubulins. Microtubules are readily disassembled and their tubulin can be reused elsewhere in the cell. In animal cells, microtubules grow out from a region called the centrosome.