3/14/2024 0 Comments Think cell 6 key generator![]() Simplified diagram of the three stages of cellular metabolism that lead from food to waste products in animal cells. As illustrated in Figure 2-70, oxidation occurs in two further stages of cellular catabolism: stage 2 starts in the cytosol and ends in the major energy-converting organelle, the mitochondrion stage 3 is entirely confined to the mitochondrion. After digestion, the small organic molecules derived from food enter the cytosol of the cell, where their gradual oxidation begins. ![]() (A membrane that surrounds the lysosome keeps its digestive enzymes separated from the cytosol, as described in Chapter 13.) In either case, the large polymeric molecules in food are broken down during digestion into their monomer subunits-proteins into amino acids, polysaccharides into sugars, and fats into fatty acids and glycerol-through the action of enzymes. Stage 1 in the enzymatic breakdown of food molecules is therefore digestion, which occurs either in our intestine outside cells, or in a specialized organelle within cells, the lysosome. The breakdown processes must act on food taken in from outside, but not on the macromolecules inside our own cells. The proteins, lipids, and polysaccharides that make up most of the food we eat must be broken down into smaller molecules before our cells can use them-either as a source of energy or as building blocks for other molecules. Food Molecules Are Broken Down in Three Stages to Produce ATP
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