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Cytoskeleton & Cell Membranes: 3.2B. Cytoskeleton & Cell Membranes. Cytoskeleton. The cytoskeleton provides the internal framework of an animal cell much like our skeletons provide our internal framework.
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Cytoskeleton & Cell Membranes: 3.2B Cytoskeleton & Cell Membranes
Cytoskeleton • The cytoskeleton provides the internal framework of an animal cell much like our skeletons provide our internal framework. • The cytoskeleton is composed of an intricate network of protein fibers anchored to the inside of the plasma membrane.
Cytoskeleton • By linking one region to another, they support the shape of the cell, much as steel beams anchor the sides of a building together. • Other fibers attach the nucleus and other organelles to fixed locations in the cell.
Cytoskeleton • Because protein fibers are too small for a light microscope to reveal, biologists visualize the cytoskeleton by attaching fluorescent dyes to antibodies.
Cytoskeleton Fibers There are three types of cytoskeleton fibers • Long slender microfilamentsmade of the protein actin. • Hollow tubes called microtubules made of the protein tubulin • Thick ropes of protein called intermediate fibers
Cytoskeleton: Actin Fibers • The actin fibers of the microfilaments form a network just beneath the cell surface that is anchored to membrane proteins embedded within the cell membrane.
Cytoskeleton: Actin Fibers • By contracting or expanding, actin plays a major role in determining the shape of animal cells by pulling the plasma membrane in some places and pushing it out in others.
Cytoskeleton: Microtubules • Microtubules within the cytoskeleton act as a highway system for the transportation of information from the nucleus to different parts of the cell. • RNA molecules are transported along microtubular “rails” that extend through the interior of the cell like train tracks.
Cytoskeleton: Intermediate Fibers • Intermediate Fibers of the cytoskeleton provide a frame on which ribosomes and enzymes can be confined to particular regions of the cell. • The cell can organize complex metabolic activities efficiently by anchoring particular enzymes near one another.
The Cell Membrane: Lipids • The cytoplasm of a cell is contained by it’s membrane. • Cell membranes are not rigid like an eggshell but fluid like a soap bubble.
The Cell Membrane: Lipids • The fluidity of a cell membrane is caused by lipids. • Lipids form a barrier that separates inside the cell from outside the cell.
The Cell Membrane: phospholipids • This lipid barrier in the cell membrane only allows certain substances to pass through in or out. • This ability to control what enters or leaves the cell is caused by the way phospholipids interact with water.
The Cell Membrane: phospholipids • A phospholipid is a lipid made of a phosphate group and two fatty acids.
The Cell Membrane: • As shown at right, a phospholipid has both a polar “head” and two nonpolar “tails”. • The head of a phospholipid is polar and is attracted to water. • In contrast, the two fatty acids, the “tails” are nonpolar and therefore they are repelled by water.
The Cell Membrane • In a cell membrane, the phospholipids are arranged in a double layer called a lipid bilayer. • The lipid bilayerallows lipids and substances that dissolve in lipids to pass through. phospholipids
Member Proteins • Various proteins are located in the lipid bilayer of a cell membrane. • The motion and fluidity of phospholipids enables some membrane proteins to move around within the lipid bilayer.
Member Proteins Cell membranes contain different types of proteins, among them. • Marker proteins which attach to carbohydrates. • Receptor proteins bind specific substances.
Member Proteins Cell membranes contain different types of proteins, among them. • Enzymes embedded in the cell membrane are involved in biochemical reactions within the cell. • Transport proteins aid the movement of substances into and out of the cell.
