The Difference Between the Oft-confused Lysosomes and Peroxisomes

Difference Between Lysosomes and Peroxisomes
Lysosomes and peroxisomes are both small organelles found in the cell. Both carry out very similar processes, but both have quite different functions. Because of the similarity in the names, one tends to confuse one for the other.
The basic fundamental, structural and functional unit of any multicellular organism is the cell. Cells are the smallest units of organization of multicellular organisms. But even within a single cells, many processes take place simultaneously. The different cellular processes can be broadly classified into three types - catabolic, anabolic and regulatory processes. Catabolism and anabolism together make up metabolism. Metabolism deals with nutrition of the body. However apart from that, the cell also has to perform maintenance functions - recycling of cellular organelles, functions related to immunity, functions to overcome the wear and tear of the cell, and finally apoptosis (programmed cell death).
Lysosomes and peroxisomes help in such 'maintenance' functions. However, as a new student of cell biology, one may get confused between the two. Though there are many clear and distinct difference between the two, there are some over-lapping facts as well. Given below is a brief account of the two organelles. More information can be found in books on molecular cell biology written by Bruce Alberts and Lodish - but I am guessing you already know about these bibles of cell biology, as a student of the subject!
Lysosomes
Lysosomes are the scavengers of the cell; they are the garbage-men that help keep cells clean of debris and unwanted metabolite. Lysosomes originate from endosomes that bud off from the Golgi apparatus. The endosomes are packed with hydrolytic enzymes, that make them lysosomes. The insides of lysosomes are at a much lower pH than the rest of the cell - lysosomes are acidic cell organelles. Lysosomes contain several lytic enzymes that help in the breakdown of unwanted things in the cell - old organelles, invading pathogens, etc. Lysosomes also help in digesting 'food' coming into the cells. The general way in which lysosomes operate is: they fuse with 'containers' called vacuoles and release their contents inside the vacuoles. The enzymes then digest and degrade whatever is present inside the vacuoles. The reason to do this is - if all the enzymes contained within lysosomes were spilled inside the cell into its cytoplasm, they would end up degrading the cell itself! Lysosomes hence have a job with great responsibility, as must be evident. The functions of lysosomes are discussed below in brief.
✦ The principal function of lysosomes is degradation of various biological metabolites and polymers and also old cell organelles and invading pathogens. Lysosomes contain a battery of different enzymes such as lipases (degrade lipids), proteases (degrade proteins), amylases (degrade starch), nucleases (degrade nucleic acids) etc. All these are used to degrade a host of different things.

✦ One of the three principal functions of lysosome is phagocytosis. One of the steps in the process of phagocytosis is when the lysosome fuses with the phagosome - resulting in a phagolysosome. This process brings the bacteria or invading pathogen and the battery of degradative lysosomal enzymes in a single space and aids in killing of the pathogen. The metabolites released as a result are recycled and used by the cell.

Endocytosis is another important lysosomal functions. The cell has many receptors (usually proteinic in nature) which help in cell-to-cell communication, in uptake of food, even antibodies are first seen as membrane bound receptors. These receptors are regularly recycled by bringing them inside the cell (endocytosis), degrading them and reusing the metabolites released.

✦ The other cellular organelles - such as mitochondria - also need to be recycled. This is achieved by the fusion of lysosomes with the organelle - a process called autophagy. Autophagy helps cell to revitalize itself.
Process of apoptosis
✦ Autophagic function of lysosomes also helps indirectly in a process called apoptosis. Apoptosis - or programmed cell death - is when a cell becomes 'old', or gets infected by certain kinds of pathogens and receives the signal for self-destruction. The contents of the lysosome then 'spill' out into the cell and eat up the cell from the inside.
✦ Immunity is the body's ability to fight invasion by disease-causing microorganisms. The ability to aid apoptosis and kill phagocytosed pathogens make lysosomes important in conferring immunity onto the organism.
Peroxisomes
The most important aspect of peroxisomes is fatty acid metabolism. They are hence different from lysosomes in that they are involved in metabolism rather than in maintenance of the cell. Peroxisomes are morphologically similar to lysosomes - the reason why many confuse between the two. However, peroxisomes do not originate from endosomes; they are assembled from different proteins (or polypeptide chains) synthesized in the cell by ribosomes. The importance and significance of the organelle becomes evident when we take a look at its function.
✦ The main function of peroxisomes becomes evident if we look at the etymology of the term 'peroxisome' - 'per' comes from peroxides, 'oxi' from oxidation; so peroxisomes are thus organelles that carry out oxidation reactions that lead to the production of peroxides.

✦ Detoxification of various toxic compounds that enter the bloodstream is also done by peroxisomes. This is typical to the peroxisomes. Peroxisomes use the hydrogen peroxide (H2O2) generated during oxidation to detoxify the toxic compounds. This is called peroxidation.

✦ Peroxisomes in the liver help in detoxification of alcohol. Around 25% of the alcohol we consume is eliminated from the body in this way.

✦ Peroxisomes play a crucial role in fatty acid metabolism, as stated before. Peroxisomes synthesize plasmalogens - a component of the cell membrane of such tissues as the brain and the heart. At the same time peroxisomes are also the site for β-oxidation of fatty acids.

✦ In plants, peroxisomes play a very important role in the seeds. The fatty acids present in the seeds are broken down in the peroxisomes to provide energy for the new budding plant to grow as the seed germinates. The fatty acids are converted to sugars which provide energy.

✦ Another important function served by peroxisomes in the plants cells is that during the Calvin cycle. Peroxisomes help to recycle phosphoglycolate - a by-product of the Calvin cycle. This is a very important function, as if the recycling didn't happen a lot of the cell's energy and carbon would be lost.
Both the organelles are important for proper functioning of the cells and to maintain the cell in a healthy condition. Studying cell biology is rather fascinating as it makes us realize that even the smallest of things are there in the cell for a reason. Hope you have fun exploring this miniature world that resides in your body!
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