The Golgi Apparatus PDF

The Golgi apparatus (Golgi body, Golgi complex) consists of a stack-like collection of flattened membranous sacs. One side of the stack of membranes is formed by the fusion of membranes of vesicles from RER or SER. At the opposite side of the stack, vesicles are formed from swellings at the margins...

The Golgi apparatus (Golgi body, Golgi complex) consists of a stack-like collection of flattened membranous sacs. One side of the stack of membranes is formed by the fusion of membranes of vesicles from RER or SER. At the opposite side of the stack, vesicles are formed from swellings at the margins that again become pinched off. The Golgi apparatus occurs in all cells, but it is especially prominent in metabolically active cells -- for example, secretory cells. More than one may be present in a cell. It is the site of synthesis of specific biochemicals, such as hormones, enzymes or others. Here specific proteins may be activated by addition of sugars (forming glycoprotein) or by the removal of the amino acid, methionine. These are then packaged into vesicles. In animal cells these vesicles may form lysosomes. Those in plant cells may contain polysaccharides for cell wall formation.Mitochondria appear mostly as rod-shaped or cylindrical organelles in electron micrographs. Occasionally their shape is more variable. They are relatively large organelles, typically 0.5--1.5μm wide, and 3.0--10.0μm long. Mitochondria are found in all cells and are usually present in very large numbers. Metabolically very active cells will contain thousands of them in their cytoplasm -- for example, in muscle fibres and hormonesecreting cells. The mitochondrion also has a double membrane (Figure 1.16). The outer membrane is a smooth boundary, the inner is infolded to form cristae. The interior of the mitochondrion is called the matrix. It contains an aqueous solution of metabolites and enzymes, and also small circular lengths of DNA. The mitochondrion is the site of the aerobic stages of respiration and the site of the synthesis of much ATP (see page 22). Mitochondria (and chloroplasts) contain ribosomes, too. They appear as tiny dark dots in the matrix of the mitochondria, and are slightly smaller than the ribosomes found in the cytosol and attached to RER.