Student Question

How do organelles within the cytoplasm of a cell

produce and package enzymes to form lysosomes?

Expert Answers

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The cell's endomembrane system consists of the nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes, vacuoles and the plasma membrane. They are continuous or can be connected via tiny vesicles that can transfer materials from one part of a cell to the next.

The endoplasmic reticulum contains both smooth and rough ER. Rough ER contains bound ribosomes which are tiny factories that can manufacture proteins. The rough ER distributes transport vesicles which are secretory proteins surrounded by membranes. The Golgi apparatus are membranous sacs that can modify ER products and sort and package materials into transport vesicles.

Proteins destined to be incorporated into a lysosome are formed by rough ER, travel to the Golgi apparatus to be further modified and the vesicle containing those proteins that buds off the Golgi apparatus is the newly formed lysosome. 

Lysosomes are membranous sacs of hydrolytic enzymes capable of digesting large molecules. 

One function of a lysosome is seen in a cell that carries out phagocytosis. When a cell engulfs another, the engulfed cell becomes a food vacuole. A lysosome will then fuse with the food vacuole and its hydrolytic enzymes digest the food molecules. Sometimes lysosomes digest old worn out organelles and recycle the molecules in a process called autophagy.

To summarize, proteins are built by ribosomes. Ribosomes attached to the rough ER build the enzymatic proteins destined to be incorporated into a lysosome, they travel to the Golgi apparatus to be modified and packaged into a vesicle that becomes the lysosome.

I have included a link to an animation showing the action of lysosomes during phagocytosis.

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Lysosomes are a type of cell organelles that are unique to animal cells; they are not formed in the cells of plants. Lysosomes work in a system with endoplasmic reticulum and the Golgi apparatus. This group of organelles working together is referred to as the endomembrane system.

Proteins start in the endoplasmic reticulum, where they interact with enzymes and synthesized lipids. They are grouped with proteins and amino acids into small membrane-enclosed vesicles, which have the ability to travel through cytoplasm. Their destination is the Golgi apparatus, which modifies proteins by attaching sugars. After exiting the Golgi apparatus in another membrane enclosed vesicle; some of these vesicles then travel to lysosomes. In this organelle, substances are broken down by enzymes and recycled.

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