Lysosomes: Types and Functions

• They were first of all observed by Christian de Duve in 1955.
• The lysosomes are tiny vesicles which are bounded by single membrane and are made from proteins and lipids.
• They are found in different organisms like in most of the animal cells and only in a few plant cells like yeast, fungi and in green unicellular organisms.
• They are absent in bacteria and mature mammalian erythrocytes.
• They are originated from endoplasmic reticulum or from the vesicles of the Golgi complex.
• They contain many enzymes about 40 kinds of enzymes that are involved in intracellular digestion.
• The enzyme includes proteases that helps in protein digestion, nucleases, glycosidases (helping in digestion of polysaccharides), lipases, phosphatases (phosphate linked compounds) and sulphatases (sulphate linked compounds).
• The internal pH of the lysosome is about 5, which is two units lower than that of the cytoplasm.
• So, the hydrolytic enzymes within the lysosomes function optimally at this pH.
• These hydrolytic enzymes are nonspecific in their activity and could potentially destroy key cellular macromolecules if not contained.

Types of Lysosomes

The lysosomes are grouped into four types. They are:

i) Primary lysosome: These are newly formed small bodies which contain hydrolytic enzymes in inactive state and are the pinched off  vesicle from the golgi apparatus.

ii) Secondary lysosome: The primary lysosome fuses with the vacuoles containing extracellular or intracellular substances and form secondary lysosome. They are also known as heterophagosomes or digestive vacuoles.

iii) Residual body: The lysosomes with undigested bodies are called residual bodies. These are also called tertiary lysosomes.

iv) Autophagic vacuole: Lysosomes are able to digest cell organelles due to which they are known as autophagic lysosomes.

Functions

• They digest the particles that enter the cell like food particles.
• In some pathological conditions, the lysosomes start to digest the various cell organelles and cause ultimately the death of the cell which is known by the process autolysis or cellular autophagy.
• For this reason, the lysosomes are also known as suicidal bags.
• They digest disease causing microorganisms.
• They also digest worn-out and the dead cells.

• The lysosomes of sperms discharge their enzymes and digest the limiting membrane of the ovum at the time of fertilization.
• Lysosomes are involved in formation of bone cells as well as their destruction.
• Ageing of cells as well as parthenogenetic development are also related with lysosomal activity.
• Lysosomes have been found to be involved in protein synthesis in case of some birds.
• They have role in metamorphosis of frog.

References: 

i) https://www.biologydiscussion.com/lysosomes/lysosomes-discovery-types-and-functions-organelles/70461

ii) https://www.microscopemaster.com/lysosomes.html

iii) https://microbenotes.com/lysosomes-structure-enzymes-types-functions/

Lysosomes: Types and Functions