Cytoskeleton Network of protein fibers extending

throughout the cytoplasm Function in providing for both structural

support and cell motility Require interaction of the cytoskeleton with

motor proteins Three main kinds of fibers make up the

cytoskeleton:

Figure 7.20 The cytoskeleton

Table 7.2 The structure and function of the cytoskeleton

Microtubules Hollow rods Composed of globular proteins called

tubulins Functions:

Cellular support Tracks for organelle movement Separation of chromosomes during cell

division Involved in the motility of the cell

Figure 7.x3 Actin

Figure 7.x4 Actin and keratin

Centrosomes and centrioles

Centrosome – region located near the nucleus

Centriole – pair of cylindrical structures located in the centrosome of animal cells Composed of nine sets of triplet microtubules

arranged in a ring May organize microtubule assembly during

cell division

Figure 7.22 Centrosome containing a pair of centrioles

Cilia and flagella Locomotor organelles formed from a

specialized arrangement of microtubules Unicellular eukaryotic organisms are

propelled through water by cilia or flagella

Motile sperm cells (animals, algae, some plants) are flagellated

May function to draw fluid across the surface of stationary cells (ciliated cells lining trachea)

Figure 7.23 A comparison of the beating of flagella and cilia

Figure 7.23x Sea urchin sperm

Figure 7.21 Motor molecules and the cytoskeleton

Figure 7.24 Ultrastructure of a eukaryotic flagellum or cilium

Figure 7.25 How dynein “walking” moves cilia and flagella

Microfilaments (actin filaments)

Solid rods Composed mainly of proteins called actin Function:

Helps supports the cell’s shape

Participate in muscle contraction

Responsible for localized contraction of cells (dividing animal cell)

Microfilaments function (cont.) Elongation and contraction of

pseudopodia during amoeboid movement Involved in cytoplasmic streaming found

in plant cells

Cytoplasmic streaming (cyclosis) – flowing of the entire cytoplasm around the space between the vacuole and plasma membrane in a plant cell

Figure 7.26 A structural role of microfilaments

Figure 7.27 Microfilaments and motility

Intermediate filaments More permanent than microtubules or

microfilaments Constructed from keratin subunits Function:

Specialized for bearing tension Reinforce cell shape Fix organelle position