CytosolMetabolism, protein synthesis (free ribosomes)CytoskeletonCell shape and movement, intracellular transportNucleusGenome (22 autosomes and 2 sex chromosomes), DNA and RNA synthesisMitochondriaATP synthesis by oxidative phosphorylation, Ca2+ storageSmooth endoplasmic reticulumSynthesis of lipids, Ca2+ storageFree ribosomesTranslation of mRNA into cytosolic proteinsRough endoplasmic reticulumTranslation of mRNA into membrane associated proteins or for secretion out of the cellLysosomeIntracellular degradationEndosomeCellular uptake of cholesterol, removal of receptors from the plasma membrane, uptake of small molecules and water into the cell, internalization of large particles (e.g., bacteria, cell debris)Golgi apparatusModification, sorting, and packaging of proteins and lipids for delivery to other organelles within
ATP, adenosine triphosphate; mRNA, messenger RNA.
inner or outer surfaces of the membrane, often by binding molecules that contain a charged (or polar) hydrophilic to the integral membrane proteins. head and two (nonpolar) hydrophobic fatty acyl chains (
Fig.
1.3 ). The amphipathic nature of the phospholipid molecule Membrane Lipids is critical for the formation of the bilayer: The hydrophobic The major lipids of the plasma membrane are phospholipids fatty acyl chains form the core of the bilayer, and the polar and phosphoglycerides. Phospholipids are amphipathic head groups are exposed on the surface.
• Fig. 1.2 Schematic diagram of the cell plasma membrane. Not shown are lipid rafts. See text for details. (Modified from Cooper GM. The Cell—A Molecular Approach. 2nd ed. Washington, DC: Sinauer; 2000, Fig. 12.3.)
Phospholipid Glycolipid (e.g., phosphatidylcholine) (e.g., galactosylceramide) Cholesterol
Sugar (e.g., galactose) • Fig. 1.3 Models of the major classes of plasma membrane lipids, depicting the hydrophilic and hydrophobic regions of the molecules. The molecules are arranged as they exist in one leaflet of the bilayer. The opposing leaflet is not shown. One of the fatty acyl chains in the phospholipid molecule is unsaturated. The presence of this double bond produces a “kink” in the fatty acyl chain, which prevents tight packing of membrane lipids and increases membrane fluidity. (Modified from Hansen JT, Koeppen BM: Netter’s Atlas of Human Physiology. Teterboro, NJ: Icon Learning Systems; 2002.)