Lysosomes

Lysosomes: Lysosomes are membrane(single membrane of a phospholipid bilayer) bounded subcellular organelle that is found in all eukaryotic cells  except blood cells, with hydrolytic enzymes (digestive enzymes)  and is responsible for the cell’s digestion of macromolecules, old cell parts, and microorganisms. It has 50 different enzymes, which are all optimally active at an acidic environment . Each lysosome is surrounded by a membrane ,interior it maintains an acidic environment (ph 4.5) ,when compared with cytoplasm through proton pump. This pumping requires expenditure of energy in the form of ATP hydrolysis, since it maintains approximately a hundredfold higher H⁺ concentration inside the lysosome. The enzymes of lysosomes are so powerful If they were not enclosed, the enzymes contained within lysosomes could cause damage to other structures within the cell. So lysosomal enzymes are inactive in neutral environment  that means they are generally inactive in cytoplasm.  
Lysosome is Spherical shape and approximately 1 μm size, It is single membrane of a phospholipid bilayer which contain acid hydrolases.

Lysosomes formation from Endoplasmic Reticulum:
Lysosomal enzymes(peptides) are synthesized in the endoplasmic reticulum (ER)and mannose 6-phosphate is added to these peptides . They are further transported to the Golgi apparatus which "packs" them into lysosomal vesicles.

Lysosomes formation from Golgi Apparatures:
Lysosomes originate by budding off from the membrane of the trans-Golgi network, a region of the Golgi complex responsible for sorting newly synthesized proteins, which may be designated for use in lysosomes, endosomes, or the plasma membrane.

Lysosomes might be differentiated into four types depending upon their content during their function namely, primarly lysosome, secondary lysosome, residual body and autophagic vacuoles.

Primary lysosome are small saclike structures enclosing enzymes synthesized by the ribosomes.  Since they store enzymes, they are also said to be storage granules. 

Secondary lysosome are formed by the fusion of primary lysosome with phagosomes.  They contain engulfed materials and enzymes. The materials are progressively digested by the enzymes.  So it is also otherwise called as digestive vacuole.

Residual bodies are nothing but secondary lysosomes with undigested wastes.  The digested materials are diffused into the cell cytoplasm through the lysosomal membrane.

Autophagic lysosomes are special type of lysosmes, which are formed when the cells feed on their own intracellular organelles and they digest them ultimately.  This happens only during starvation of organisms.

Lysosomal functions are dependent on lysosomes fusing with target vacuoles and release of digestive enzymes.
The lysosomes then fuse with membrane vesicles that derive from one of three pathways: endocytosis, autophagocytosis, and phagocytosis.
Endocytosis: extracellular macromolecules are taken up into the cell to form membrane-bound vesicles called endosomes that fuse with lysosomes.
Autophagocytosis: is the process by which old organelles are removed from a cell also called autolysis; they are enveloped by internal membranes that then fuse with lysosomes. Autolysis plays a central role in many apoptotic cascades.
Phagocytosis: is carried out by specialized cells ( macrophages) that engulf large extracellular particles such as dead cells or foreign invaders ( bacteria) and target them for lysosomal degradation. Many of the products of lysosomal digestion, such as amino acids and nucleotides, are recycled back to the cell for use in the synthesis of new cellular components.

Lysosomal Diseases:
Lysosomes contain about 50 different degtive enzymes. Mutations in the genes that encode these enzymes are responsible for more than 30 diffradaerent human genetic diseases, which are called lysosomal storage diseases because undergrad material accumulates within the lysosomes of affected individuals. Most of these diseases result from deficiencies in single lysosomal enzymes.

S.No.	Disease	Substance accumulated	Enzyme defect
1.	Ceramide   lactoside	Ceramide lactoside	β-glactoidase
2.	Gaucher’s disease	Glucocerebroside	β-glactosidase
3.	Generalized gangliosidosis	Ganglioside GM,	β-gloctosidase
4.	Krabbe’s disease	Galactocerebroside	β-glactosidase
5.	Meta chromatic leucodystrophy	Ceramide glactose -3 sulphate	Sphingomyelinase
6.	Niemamnn-Pick disease	Sphingomyelin	Sphingomyelinase
7.	Tay- Sach’s disease	Ganglioside GM,	Hexosaminidase-A
8.	Type II glyco­ genosis	Glycogen	α- Glycosidase.
9.	Fabry’s disease	Ceramide trihexodise	α-Glactosidase