AP Biology The Cell Membrane

AP Biology 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  Form boundary for the organelles  Compartmentalize chemical reactions

AP Biology Summary Section 2 – pages Parts of the Plasma Membrane Glycerol Backbone Two Fatty Acid Chains Phosphate Group 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.

AP Biology Summary Section 2 – pages 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 NON-POLAR, and water-fearing or repelled by water hydrophilic hydrophobic

AP Biology Membrane Structure All membranes are phospholipid bilayers with embedded proteins. Label the: Hydrophilic heads Hydrophobic tails OUTSIDE CELL INSIDE CELL PLASMA MEMBRANE

AP Biology  A membrane is a mosaic  Proteins and other molecules are embedded in a framework of phospholipids  A membrane is fluid  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 Summary Section 2 – pages The cholesterol prevents the fatty acid chains of the phospholipids from sticking together. Cholesterol Molecule PLASMA MEMBRANE Cholesterol molecules are found throughout the plasma membrane.

AP Biology  Embedded in the bilayer are proteins  Most of the membrane’s functions are accomplished by the embedded proteins.  Integral proteins implanted in the membrane- partway or all the way across  Peripheral proteins are on one side or the other of the membrane Parts of the Plasma Membrane

AP Biology Peripheral Proteins Types of Membrane Proteins 1. Recognition proteins 2. Integrins 3. Cell junction proteins 4. Enzymes 5. Receptor proteins 6. 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 Activated molecule Receptor

AP Biology  Recognition Proteins - identify type of cell and identify a cell as “self” versus foreign - 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  The cell expends energy to transport water soluble substances against their concentration gradient

AP Biology Fig. 5-1d

AP Biology  Membrane becomes semi-permeable via protein channels  specific channels allow specific material across cell membrane inside cell outside cell sugaraa H2OH2O salt NH 3