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Lysosomes, Peroxisomes & Secretory Vesicles

• are membrane-bound vesicles.

• are formed from endoplasmic reticulum-Golgi apparatus system.

Lysosomes

• Formed by breaking off from Golgi apparatus → disperse throughout the cytoplasm.

• 250 to 750 nm in diameter.

• Contains hydrolase enzymes that break larger molecules into fragments. e.g.

  • Proteases hydrolyze proteins into amino acids.

  • Amylases hydrolyaze polysaccharides into monosaccharides.

  • Lipases hydrolyze lipids into fatty acids and triglycerol.

Functions

• Lysosomes are cell's digestive system. They degrade...

  • Damaged cellular structures.

  • Food particles.

  • Unwanted materials e.g. bacteria.

• Recently lysosomes are found to be involved in secretory functions also.

Types

• Primary Lysosomes

  • are freshly formed inactive lysosomes.

• Secondary Lysosomes

  • are formed by fusion of primary lysosome with phagosome or endosome.

  • are actively digesting things.

Peroxisomes

• are formed by pinching off from smooth endoplasmic reticulum.

• Contains oxidase enzymes e.g. catalase

Functions

• Catabolize long-chain fatty acids (β oxidation)

• Detoxification: Oxidizes toxic substances that may be harmful to the cell.

Secretory vesicles

• are also called secretory granules.

are formed from Golgi apparatus

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Store substances that are to be released out of the cell

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When cell is stimulated for release

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Content of secretory vesicles is released intracellularly by exocytosis.

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