The Many Functions Of Lysosomes

The lysosomes (12) break down old cell organelles and other materials, freeing up macromolecules for use. Photo: By Kelvinsong - Own work, CC0,

The cells of both plants and animals have many different organelles. Organelles perform different functions that help the cell survive and replicate, and one of the organelles, the lysosome, carries out a wide variety of functions. Lysosomes are responsible for a number of different functions, including recycling old cells, digesting materials that are both inside and outside of the cell, and releasing enzymes. Let’s take a deep dive into the lysosomes and explore their various important functions in greater detail.

Definition of a Lysosome

Lysosomes are membrane-bound organelles which are found in animal cells. Some plant cells are thought to have lysosomes, though there is some debate on the matter. They have a single outer membrane, consisting of a phospholipid bilayer. The phospholipid bilayer means that one half is hydrophobic, avoiding water, while the hydrophilic half loves water. The membrane contains acids and enzymes capable of digesting and decomposing macromolecules. Macromolecules are molecules with a large number of atoms, such as nucleic acids, synthetic polymers, and proteins.

Layout of a lysosome. Photo: National Library of Medicine, National Institutes of Health.

How Are Lysomes Created?

Lysosomes are created by another organelle called the Golgi Body, or Golgi Apparatus. The Golgi Body is found in most eukaryotic cells. The Golgi Body creates vesicles, which bud off from the organelle and become primary lysosomes. Secondary lysosomes can also be created through the process of fusion. Primary lysosomes can fuse together with other vesicles in the cell membrane to create secondary lysosomes.

Functions of a Lysosome:

  • Intracellular Digestion
  • Protein Synthesis
  • Breaking Down Dead Cells

The Main Functions Of Lysosomes

The general function of lysosomes is to degrade or break down macromolecucles. This includes processing old and worn out cell parts to recycle their components and making harmful toxins or bacteria safe by degrading them. They process many of the vacuoles which move either in or out of the cell, ensuring things run smoothly.  Lysosomes are essentially the garbage disposal or recycling units of cells in this sense. Lysosomes have many different functions, including handling exocytosis, autophagy, heterophagy, and biosynthesis.

Exocytosis is how materials leave a cell through the cell membrane. ATP, energy, is used to transport the vacuole containing material outside of the cell. The lysosomes which are responsible for this process are called secretory lysosomes.

Autophagy refers to how materials are broken down, or digested, within a cell. Organelles within a cell wear out after time, and when they are worn out the lysosome breaks them down so that the macromolecules that comprise them can be used to create other structures and organelles. Structures called autophagosomes are created, which encapsulate the material that is to be broken down. The autophagosomes then bond with the lysosome by fusing with the lysosomal membrane. After this, the autophagosomes are broken down. While autophagy refers to the process which degrades materials on the inside of the cell, heterophagy involves the digestion of materials outside of the cell body.

A phagosome has fused with a lysosome, which will begin digesting it. Photo: Khan Academy

Vacuoles containing a variety of different materials are found outside of the cell, and once absorbed through the cell membrane the lysosomes fuse with the vacuoles and begin digesting them. Vacuoles outside the cell can contain a variety of different compounds. For example, white blood cells are types of phagocytes. These cells defend the body from attackers, encapsulating harmful substances or bacteria. The phagocytes are then broken down by the lysosomes, which disposes of the threat.

Heterophagy can also include pinocytic and endocytic processes. The pinocytic process is how cells take in extra-cellular fluid, and it plays an important role in the immune system as it enables immune surveillance. Endocytosis is how cells can take in particles that have attached to the outside of the cell. It’s a form of active transport, and cells invaginate to absorb the molecules on the outside of the cell. The absorbed molecules are then sent to the lysosomes for break-down.

Biosynthesis, the process by which materials are recycled for later use, takes place mainly in the lysosomes. The lysosomes also break down cells which have died, harvesting their macromolecules to make new organelles and cells, in a process known as autolysis.

Other Functions Of Lysosomes

Though the main function of lysosomes is to process and recycle old or harmful material, they are also involved in a number of other biological processes and functions.sosomes

Recent research has suggested that lysosomes could play a role in the act of protein synthesis. Proteins are what enable cells to carry out a wide variety of functions, and they are created through the interactions between ribosomes and RNA. Lysosomes may have something to do with cell metabolism, at least in the case of the livers and kidneys of birds. Lysosomal enzymes with also play a role in fertilization, as sperm release lysosomal enzymes that help them penetrate eggs.

Lysosomes are thought to help bone cells form, in addition to aiding in their degradation. Lysosomal enzymes are released by the osteoclasts, which remove bone by degrading the organic matrix.

What Happens When Lysosomes Malfunction

Since lysosomes are so integral to the health of a cell, enabling it to degrade material and create new organelles out of the parts, if a lysosome malfunctions the results can be quite harmful to the cell. A lysosomal malfunction can lead to the problems like the buildup of excess sugars or lipids. Lysosomal storage diseases are typically caused by defective genes, and children can inherit one or both defective genes from their parents. Though rare, lysosomal storage diseases can be life-threatening.

Lysosomal storage diseases can kill cells over time, impacting the functioning of many different organs, including the liver, spleen, and brain. These disorders can be fatal. Examples of lysosomal storage diseases include Tay Sachs disease, Krabbe disease, and metachromatic leukodystrophy.

Lysosomes are extremely important to the health of a cell. If a cell didn’t have lysosomes within it, it wouldn’t be able to break down old and dying cell components, nor would it be able to digest and break down proteins. For these reasons animal cells are dependent upon their lysosomes.

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