Synthesis of other cellular constituents (such as membrane phospholipids and certain required metabolites)
Cellular movements, including muscle contraction, crawling movements of entire cells, and movement of chromosomes during mitosis
Transport of molecules against a concentration gradient
Generation of an electric potential across a membrane (important for nerve function)
▲ FIGURE 1-14 ATP is the most common molecule used by cells to capture and transfer energy. ATP is formed from ADP and inorganic phosphate (Pj) by photosynthesis in plants and by the breakdown of sugars and fats in most cells. The energy released by the splitting (hydrolysis) of P; from ATP drives many cellular processes.
merous proteins composing the various working compartments must be transported from where they are made to their proper locations (Chapters 16 and 17). Some proteins are made on ribosomes that are free in the cytosol. Proteins secreted from the cell and most membrane proteins, however, are made on ribosomes associated with the endoplasmic reticulum (ER). This organelle produces, processes, and ships out both proteins and lipids. Protein chains produced on the ER move to the Golgi apparatus, where they are further modified before being forwarded to their final destinations. Proteins that travel in this way contain short sequences of amino acids or attached sugar chains (oligosaccharides) that serve as addresses for directing them to their correct destinations. These addresses work because they are recognized and bound by other proteins that do the sorting and shipping in various cell compartments.
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