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Transcript
The Cell Membrane AP Biology 2007-2008 Membrane Function Outer plasma membrane Forms a boundary between a living cell and its surroundings (prok and euk cells) Exhibits selective permeability Controls traffic of molecules in and out Internal organelle membranes AP Biology Form boundary for the organelles Compartmentalize chemical reactions Parts of the Plasma Membrane Phospholipids are the main component of a plasma membrane. They are lipids made of a phosphate molecule, a glycerol molecule, and two fatty acid chains. Phosphate Group Glycerol Backbone Two Fatty Acid Chains AP Biology The head of the phospholipid molecule is attracted to water, whereas, the glycerol and two fatty acid tails are repelled by water. POLAR, and water-loving or attracted to water hydrophilic NON-POLAR, and water-fearing or repelled by water hydrophobic AP Biology Membrane Structure All membranes are phospholipid bilayers with embedded proteins. OUTSIDE CELL Label the: PLASMA Hydrophilic heads Hydrophobic tails AP Biology INSIDE CELL MEMBRANE A membrane is a mosaic Proteins and other molecules are embedded in a framework of phospholipids A membrane is fluid AP Biology Most protein and phospholipid molecules can move laterally AP Biology Glycoproteins and glycolipids are proteins and lipids with short chain carbohydrates attached on the extracellular side of the membrane. These carbohydrate chains act as antennae, receiving chemical messages from other cells. They are also markers & identifiers that identify the cell to other cells. AP Biology PLASMA MEMBRANE Cholesterol molecules are found throughout the plasma membrane. Cholesterol Molecule The cholesterol prevents the fatty acid chains of the phospholipids from sticking together. AP Biology Parts of the Plasma Membrane Embedded in the bilayer are proteins Most of the membrane’s functions are accomplished by the embedded proteins. AP Biology Integral proteins implanted in the membrane- partway or all the way Peripheral Proteins Types of Membrane Proteins 1. 2. 3. 4. 5. 6. Recognition proteins Integrins Cell junction proteins Enzymes Receptor proteins Transport proteins – Passive and active AP Biology Adhesion Proteins - Integral - Help cells of the same type stick together in a tissue. AP Biology Communication Proteins - Integral - Match with an identical protein on another - cell and form a channel, which directly connects two cell’s cytoplasm Chemical signals flow through the channels. AP Biology Receptor proteins - bind hormones and other substances on the outside of the cell. Binding triggers a change inside the cell. Called signal transduction Example: The binding of insulin to insulin receptors causes the cell to let glucose transport into the cell. AP Biology Fig. 5-1c Messenger molecule Receptor Activated molecule AP Biology Recognition Proteins - identify type of cell and identify a cell as “self” versus foreign Most are glycoproteins Carbohydrate chains vary between species, individuals, and even between cell types in a given individual. Glycolipids also play a role in cell recognition AP Biology Many membrane proteins are enzymes This is especially important on the membranes of organelles. AP Biology Transport Proteins Passive Transport Proteins allow water soluble substances (small polar molecules and ions) to pass through the membrane without any energy cost Active Transport Proteins AP Biology The cell expends energy to transport water soluble substances against their concentration gradient Fig. 5-1d AP Biology Membrane becomes semi-permeable via protein channels specific channels allow specific material across cell membrane inside cell NH AP Biology 3 salt H 2O aa sugar outside cell