Lysosomes structure and function in Biology
1.3.4 Lysosomes
Lysosomes (Gk. also: splitting, soma: body) are sac-like single membrane-bounded organelles that break macromolecules in the cells.
Discovery:
These were first in 1949. Posted by Belgian biologist Christian De Duve in
and an on chills to count USE.
Occurrence:
These are found in almost all eukaryotic cells except mammalian RBCs. In plants central vacuole functions as a lysosome, therefore, lysosomes are less in number in plants. All fungi contain many lysosomes. The periplasmic space of bacteria may function as a lysosome.
Chemical Composition:
Lysosomes contain many enzymes like acid phosphatases and all types of hydrolytic enzymes, like carbohydrates, lipases, nucleases, and proteases.
Shape:
They are roughly spherical in shape.
Size:
Vary in size from 0.1-0.8μm in diameter. In phagocytic WBC it is largest in size (0.8-2μm).
Types of Lysosomes: These are known as polymorphic cellular organelles because during function exist in different morphological and physiological states.
Primary Lysosome:
Enzymes are synthesized by ribosomes of rough endoplasmic reticulum and then taken to Golgi bodies where these are processed and budded off as Golgi vesicles, called primary lysosomes.
Secondary Lysosome:
They are also called digestive vacuoles. They are formed by the fusion of primary lysosome with food vacuole known as phagosome (phagocytic food vacuole). Residual Bodies or Tertiary.
Lysosome: Lysosome containing undigested materials after the absorption of digested food into the cytoplasm is called residual lysosome. In unicellular organisms, these are removed outside of the cell by exocytosis while in multicellular organisms these are retained in the cell as lipofuscin granules.
Autophagic lysosomes:
Also called autophagosomes or cytolysosomes. When primary lysosomes fuse with dead cellular organelles such as mitochondrions which die after ten days to be digested are called autophagosomes, such cells recycle half of their macro molecules each week. human liver.
Functions of Lysosomes:
Lysosomes perform many functions inside and outside of cells.
These are under Intracellular digestion: Foreign substances received by the cells either by phagocytosis (solid molecules) or pinocytosis (liquid molecules) are digested by the lysosome. This process is called heterophagy.
The old or dead cell organelles are digested by lysosomes and stored food is also digested during starvation. This process is known as autophagy.
Extracellular digestion:
Lysosomes also help in extracellular digestion by releasing enzymes. e.g., the lysosomes of osteoclast (Bone eating cells) dissolve unwanted parts of the bone. Extracellular digestion also takes place in fungi.
Autolysis:
Sometimes all lysosomes of the cell burst to dissolve the cell completely. Thus also called suicidal bags because old cells like WBCs, platelets, and epithelial cells are removed by autolysis. It also destroys unwanted organs of embryos such as the tail of a human embryo and the tail of a tadpole.
Crinophagy:
The excess hormones of the endocrine gland may be digested by the I process known as coprophagy.
Exocytosis or cell excretion:
Sometimes enzymes of primary lysosomes are released from the cell. This occurs during the replacement of cartilage by bone during development. Similarly, the matrix of bone may be broken down during remodeling of bone that occurs in response to injury. Storage Diseases (Diseases due to faulty lysis) 186
Several congenital diseases (by birth but not hereditary) have been found to occur due to the accumulation of substances within the cell. Such as glycogen or various glycolipids.
These are caused by mutations in the genes of lysosomal enzymes. About 20 such diseases are known e.g., two of these are given below:
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