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Cell Membrane

Cell Membrane. Structure of membrane Transport across cell membranes. Structure of membrane. Generally…. The phospholipids form a thin, flexible sheet. The proteins “float” in the phospholipid sheet like icebergs. The carbohydrates extend out from the proteins. Phospholipids.

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Cell Membrane

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  1. Cell Membrane Structure of membraneTransport across cell membranes

  2. Structure of membrane

  3. Generally… • The phospholipids form a thin, flexible sheet. • The proteins “float” in the phospholipid sheet like icebergs. • The carbohydrates extend out from the proteins.

  4. Phospholipids • Polar, hydrophilic phosphate heads face outwards. • Non-polar, hydrophobic fatty acid tails face each other in the middle of the bilayer. • Hydrophobic layers allows small molecules through, but is a barrier to larger ones.

  5. Proteins • Integral proteins normally span from one side to the other. • Peripheral proteins normally sit on one of the surfaces. They can slide around the membrane very quickly, but not flip from one side to the other.

  6. Proteins • Proteins that span the membrane (integral proteins) are usually involved in transporting substances across the membrane. • Proteins on the inside of the surface of the cell membrane are often attached to the cytoskeleton and are involved in maintaining the cell’s shape. They may also be enzymes, catalysing reactions in the cytoplasm. • Proteins on the outside surface of cell membranes can act as receptors by having a specific binding site where hormones or other chemicals can bind. This binding then triggers other events in the cell. They may also be involved in cell signalling and cell recognition, or they may be enzymes, such as maltase.

  7. Carbohydrates • Attached to membrane proteins or sometimes to phospholipids. • Proteins with carbohydrates attached are called glycoproteins. • Phospholipids attached are called glycolipids.

  8. More carbs • The carbohydrates are short polysaccharides composed of a variety of different monosaccharides, and form a cell coat or glycocalyx outside the cell membrane. • The glycocalyx is involved in protection and cell recognition, and antigens such as the ABO antigens on blood cells are usually cell-surface glycoproteins.

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