Eukaryotic Cells: The Golgi Apparatus and Lysosomes (A-level Biology)
Eukaryotic Cells: The Golgi Apparatus and Lysosomes
Golgi Apparatus
- The Golgi Apparatus is a stack of curved membranes. The Golgi consists of a group of stacked, thin, fluid filled membranes near the nucleus. When observed under a microscope, many people describe them as a stack of pita bread!
- The Golgi Apparatus packages lipids and proteins. The main function of the Golgi Apparatus is to package proteins and lipids that are destined for export outside of the cell or to the cell surface membrane. Hence why many refer to it as the post office of the cell.
- The Golgi Apparatus has two “faces”.
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- The cis face receives proteins and lipids from other organelles.
- The cisternae and inner lumen of the Golgi apparatus do the packaging.
- The trans face releases the proteins or lipids after package.
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- Proteins and lipids are packed into Golgi vesicles. The proteins and lipids are packaged into special membrane bound parcels called Golgi vesicles. They are essentially envelopes for transporting the lipids and proteins to their final destinations.
- The Golgi Apparatus also makes lysosomes. See below for more details on lysosomes.
Lysosomes
- Lysosomes round membrane bound organelles. They have no distinct internal structure and are a type of Golgi vesicle.
- Lysosomes contain enzymes called lysozymes. Lysozymes are digestive enzymes which digest material in the cell. The membrane surrounding the lysosome protects the rest of the cell from their digestive activity. Lysozymes are also commonly referred to as hydrolytic enzymes (because they facilitate hydrolysis reactions).
- Lysosomes can be used to digest invading cells or digest worn out cell structures. Lysozymes are essentially the waste disposal system of the cell. The lysosomes can “eat up” broken down organelles through a process called endocytosis and then digest them down using the lysozymes. Lysosomes can do the same to invading pathogens, like bacteria, as mechanisms of defense against infections.
- Digested material can be used or excreted. The digested material can be used by the cell as building blocks to make other molecules and structures. Or they can be excreted from the cell as waste.
The Golgi Apparatus is an organelle found in eukaryotic cells. It is responsible for sorting, modifying and packaging proteins and lipids that are produced in the endoplasmic reticulum. The Golgi Apparatus acts as a processing and distribution center for these molecules, directing them to their final destinations in the cell or outside the cell.
The Golgi Apparatus has several functions, including:
Sorting and modifying proteins and lipids
Packaging molecules into vesicles
Directing molecules to their final destination within the cell or outside the cell
Participating in the synthesis of carbohydrates
The Golgi Apparatus works by receiving newly synthesized proteins and lipids from the endoplasmic reticulum and modifying them as they pass through its multiple stacked cisternae. The modifications can include adding or removing sugar groups to create glycoproteins, modifying phospholipids to create lipoproteins, and changing the protein’s conformation. The modified molecules are then packaged into vesicles and sent to their final destination, either within the cell or outside the cell.
Lysosomes are organelles in eukaryotic cells that function as cellular “digestive systems.” They contain hydrolytic enzymes that can break down a wide range of macromolecules, including proteins, carbohydrates, and lipids.
The primary function of lysosomes is to break down and recycle cellular waste and unwanted material. This includes old organelles, foreign invaders, and cellular debris. The enzymes within the lysosome can also play a role in programmed cell death (apoptosis) and in the regulation of cellular metabolism.
Lysosomes work by engulfing unwanted material, such as old organelles, foreign invaders, and cellular debris, and then using the hydrolytic enzymes within the lysosome to break down the material into smaller components. These components can then be recycled for use in other cellular processes. If a cell is damaged beyond repair, lysosomal enzymes can also contribute to the process of programmed cell death.
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