Ch 5 1 Plasma Membrane Structure and Function

Ch. 5. 1 Plasma Membrane Structure and Function AP Biology 2007 -2008

Membrane Design Cell Membrane Animation fluid-mosaic model a. Fluid = pliable/easily moved - due to lipid component -phospholipids can move laterally b. Mosaic = made of a combination of molecules (lipids, proteins, and carbs) 2 AP Biology

Phospholipids § Phosphate head u hydrophobic § Arranged as a bilayer AP Biology “attracted to water” hydrophilic § Fatty acid tails u Phosphate Fatty acid “repelled by water”

Arranged as a Phospholipid bilayer § Serves as a cellular barrier / border sugar polar hydrophilic heads nonpolar hydrophobic tails H 2 O salt impermeable to polar molecules polar hydrophilic heads waste AP Biology lipids

Cell membrane defines cell § Cell membrane separates living cell from aqueous environment u thin barrier = 8 nm thick § Controls traffic in & out of the cell u allows some substances to cross more easily than others § hydrophobic (nonpolar) vs. hydrophilic (polar) AP Biology

Permeability to polar molecules? § Membrane becomes semi-permeable via protein channels u specific channels allow specific material across cell membrane inside cell NH AP Biology 3 salt H 2 O aa sugar outside cell

Membrane Proteins § Proteins determine membrane’s specific functions u cell membrane & organelle membranes each have unique collections of proteins § Classes of membrane proteins: u peripheral proteins § loosely bound to surface of membrane § ex: cell surface identity marker (antigens) u integral proteins § penetrate lipid bilayer, usually across whole membrane § transmembrane protein § ex: transport proteins w channels, permeases (pumps) AP Biology

Example: Aquaporins let water in and out of the cell 8 AP Biology

AKA Glycoproteins Proteins with carbohydrate chains attached; carb chains act as ID markers Receive chemical signals (neurotrasmitters/hormones) to deliver messages from cell to cell 9 AP Biology

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Membrane carbohydrates § Play a key role in cell-cell recognition u u u ability of a cell to distinguish one cell from another Allows cells to stick to eachother (adhesion) important in organ & tissue development Glycoproteins and glycolipids basis for rejection of foreign cells by immune system AP Biology

Cholesterol u Modifies fluidity § High temp – stiffens membrane § Low temp – prevents membrane from freezing AP Biology

Extracellular Matrix § Only in Animal cells § Area between cells § Contain various protein fibers and complex carbohydrates § Function: assists in communication between cells AP Biology

Membrane is a collage of proteins & other molecules embedded in the fluid matrix of the lipid bilayer Glycoprotein Extracellular fluid Glycolipid Phospholipids Cholesterol Peripheral protein AP Biology Cytoplasm Transmembrane proteins Filaments of cytoskeleton

Any Questions? ? AP Biology

Plasma Membrane Structures 1. Phospholipids a. polar heads are hydrophilic “water loving” b. tails (fatty acids) are hydrophobic “water fearing” and directed inward 2. Extracellular Matrix (ECM) Only animal cells Contain various protein fibers and complex carbohydrates Function: assists in communication between cells 3. Carbohydrate Chains Glycoproteins and glycolipids Only occur on outside surface of cell membrane Function: Adhesion between cells Reception of signaling molecules Cell to cell recognition 1 6 AP Biology

Plasma Membrane Structures 4. Cholesterol u Lipid u Modifies fluidity § High temp – stiffens membrane § Low temp – prevents membrane from freezing 5. Proteins -serves many different functions u u 1 7 AP Biology Integral Peripheral