Cell Biology

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• Chapter 7
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• The fluid mosaic model is now generally accepted for the description of all biological membranes • Transmembrane segments of membrane proteins anchor membrane proteins in the lipid bilayer. • A ganglioside is not a phospholipid.

• Thin-layer chromatography separates lipids based on hydrophobicity. • Unsaturated fatty acids have double bonds and increased membrane fluidity. • Cholesterol increases fluidity at low temperatures and decreases fluidity at high temperatures. • Ankyrin is a peripheral membrane protein found in erythrocytes. Therefore it lacks discrete hydrophobic sequences. • Most lipid-anchored proteins are attached to the inner side of a plasma membrane by covalent linkage to a fatty acid or prenyl group. • A useful technique for studying membrane proteins is SDS-PAGE ( sodium dodecyl sulfate- polyacrylamide gel electrophoresis). In this method, the role of SDS is to coat the proteins with a negative charge. • Lectins are proteins that bind sugars and have been useful in the study of glycoproteins. • You discover an integral membrane protein that has amino acid residues N- and O- linked to side groups with a terminal sialic acid. It is therefore most likely a glycoprotein. • Localized regions of membrane lipids involved in cell signaling are called lipid rafts. • Hopanoids are sterol-like molecules found exclusively in bacteria. • Membranes from cells grown in media enriched with stearate are less fluid than normal membranes. This is because the membranes have more saturated fatty acids. • The functions of the biological membrane are :

• They contain receptors for the detection of external signals • They provide a means of cell to cell communication
• They regulate movement of a substance into and out of the cell • They define boundaries of a cell and its organelles
• Within a membrane, phospholipids:
• Have their polar head groups facing outward
• Can switch or “flip-flop” from one monolayer to the other •...
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