Lysosomes

Another function of the Golgi apparatus is to package certain hydrolytic (digestive) enzymes into membrane-bound packets called lysosomes. The enzymes are needed to digest nutrient molecules that enter the cell by endocytosis (Figure 3.14), and would break down the fabric of the cell itself if they were not contained within the lyso-somes. Peroxisomes are similar to lysosomes, but smaller, and also contain degradative enzymes. They contain the enzyme catalase, which breaks down the potentially toxic hydrogen peroxide generated by other breakdown reactions within the peroxisome.

Figure 3.14 Endocytosis. Membrane-bound vacuoles surround a food particle and internalise it in the form of a phagosome. This fuses with a lysosome, which releases digestive enzymes, resulting in the breakdown of the contents. The process of endocytosis is unique to eucaryotic cells. From Black, JG: Microbiology: Principles and Explorations, 4th edn, John Wiley & Sons Inc., 1999. Reproduced by permission of the publishers

Figure 3.14 Endocytosis. Membrane-bound vacuoles surround a food particle and internalise it in the form of a phagosome. This fuses with a lysosome, which releases digestive enzymes, resulting in the breakdown of the contents. The process of endocytosis is unique to eucaryotic cells. From Black, JG: Microbiology: Principles and Explorations, 4th edn, John Wiley & Sons Inc., 1999. Reproduced by permission of the publishers

Outer membrane

Inner membrane

Intermembrane space

Outer membrane

Inner membrane

Intermembrane space

Mitochondrial Structure

Figure 3.15 Mitochondrial structure. The inner membrane, the location of the electron transport chain in aerobic respiration, is formed by the invagination of the more permeable outer membrane. Mitochondria have similar dimensions to many bacteria (approx. 1-3^m), but may vary in shape due to the plasticity of their membranes

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