The Cell Membrane AP Biology Overview Cell membrane
The Cell Membrane AP Biology
Overview § Cell membrane separates living cell from nonliving surroundings u thin barrier = 8 nm thick § Controls traffic in & out of the cell u u selectively permeable allows some substances to cross more easily than others § hydrophobic vs hydrophilic § Made of phospholipids, proteins & other macromolecules AP Biology
Phosphate Phospholipids § Fatty acid tails u hydrophobic § Phosphate group head u hydrophilic Fatty acid § Arranged as a bilayer Aaaah, one of those structure–function examples AP Biology
Phospholipid bilayer polar hydrophilic heads nonpolar hydrophobic tails polar hydrophilic heads AP Biology
More than lipids… § In 1972, S. J. Singer & G. Nicolson proposed that membrane proteins are inserted into the phospholipid bilayer It’s like a fluid… It’s like a mosaic… It’s the Fluid Mosaic Model! 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
Membrane fat composition varies § Fat composition affects flexibility u membrane must be fluid & flexible § about as fluid as thick salad oil u % unsaturated fatty acids in phospholipids § keep membrane less viscous § cold-adapted organisms, like winter wheat w increase % in autumn u AP Biology cholesterol in membrane
Membrane Proteins § Proteins determine membrane’s specific functions u cell membrane & organelle membranes each have unique collections of proteins § Membrane proteins: u peripheral proteins § loosely bound to surface of membrane § cell surface identity marker (antigens) u integral proteins § penetrate lipid bilayer, usually across whole membrane § transmembrane protein § transport proteins w channels, permeases (pumps) AP Biology
Why are proteins the perfect molecule to build structures in the cell membrane? AP Biology 2007 -2008
Many Functions of Membrane Proteins Outside Plasma membrane Inside AP Biology Transporter Enzyme activity Cell surface receptor Cell surface identity marker Cell adhesion Attachment to the cytoskeleton
Membrane carbohydrates § Play a key role in cell-cell recognition u ability of a cell to distinguish one cell from another § antigens important in organ & tissue development u basis for rejection of foreign cells by immune system u AP Biology
Movement across the Cell Membrane AP Biology 2007 -2008
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