Basics only Ultrastructure, Chemical composition and Functions • Lysosome was discovered by a Belgian biologist, Christian de Duve, and was awarded a Nobel Prize in Medicine or Physiology in the year 1974. • The word “lysosome” is made up of two words “lysis” meaning breakdown and “soma” meaning body. • Lysosomes are membrane-bound specialized vesicles, dense granular structures containing hydrolytic enzymes responsible mainly for intracellular and extracellular digestion. • Lysosomes are formed by budding off of the Golgi apparatus, and the hydrolytic enzymes within them are formed in the endoplasmic reticulum. Lysosomes have an acidic interior pH level of about 5 and carry a high content of digestive enzymes. • All of the digestive enzymes found in the lysosome require an acidic environment to function properly and are called acid hydrolases. • Lysosomes cannot digest themselves - Most of the proteins present in its membrane contain high amounts of carbohydrate-sugar groups. Because of the present of these groups, digestive enzymes are unable to digest the proteins present on the membrane. • Lysosomal Storage Diseases: Some inherited metabolic disorders can cause defects in the proper functioning of lysosomes. These disorders are called lysosomal storage diseases, or LSDs. There are around 40 different LSDs.

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LYSOSOMES
INTRODUCTION
 Lysosome was discovered by a Belgian biologist, Christian de Duve, and was awarded a
Nobel Prize in Medicine or Physiology in the year 1974.
 The word “lysosome” is made up of two words “lysis” meaning breakdown and “soma”
meaning body.
 Lysosomes are membrane-bound specialized vesicles, dense granular structures
containing hydrolytic enzymes responsible mainly for intracellular and extracellular
digestion.
OCCURRENCE
 Only eukaryotic animal cells contain lysosomes.
 Prokaryotic cells, such as bacteria do not contain lysosomes or any of the other
membrane-bound organelle.
ULTRASTRUCTURE OF LYSOSOMES
 Lysosomes vary in size (0.1-1.2 µm) and shape,
but have several common features.
 They have an irregular or pleomorphic shape
but mostly they appear in spherical or granular
structure.
 The number of lysosomes also varies across
different biological tissues (1-300).
 It is surrounded by a single lipoprotein
membrane unique in composition.
 The membrane contains highly
glycosylated lysosomal associated membrane
proteins (LAMP) and Lysosomal integral
membrane proteins (LIMP).
 LAMPs and LIMPs form a coat on the inner
surface of the membrane
 They protect the membrane from attack by the
numerous hydrolytic enzymes retained inside.

Structure of Lysosome
 The lysosomal membrane has a
hydrogen proton pump (H + ions)
which is responsible for
maintaining low pH conditions of
the enzyme
 The acidic medium maintained by
the proton pump that pumps H+
inside the lumen, ensures the
functionality of the lysosomal
enzymes.
CHEMICAL COMPOSITION OF LYSOSOMES
 Lysosomes are formed by budding off of the Golgi apparatus, and the hydrolytic enzymes
within them are formed in the endoplasmic reticulum. Lysosomes have
an acidic interior pH level of about 5 and carry a high content of digestive enzymes.
 All of the digestive enzymes found in the lysosome require an acidic environment to
function properly and are called acid hydrolases.

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Lysosome contains about 50 enzymes that are grouped in to six main categories:
1. Nucleases - Nucleases are important enzymes that hydrolyze nucleic acids. Nucleases
are divided in to deoxyribonuclease (acts on DNA) and ribonuclease which hydrolyses
RNA. Hydrolysis action on nucleic acids results in the production of sugars, nitrogen
bases as well as phosphates.
2. Proteases - Proteases includes enzymes like collagenase and peptidases that acts on
proteins converting them to amino acids.
3. Glycosidases - Glycosidases like beta galactosidase act on the glycosidic bonds of
polysaccharides converting polysaccharides to monosaccharides. For instance, the
enzyme galactosidase acts on such bonds converting lactose to glucose and galactose.
4. Phosphatases - Good examples of Phosphatases are acid phosphodiesterases. These are
important enzymes that act on organic compounds releasing phosphate in the process.
However, the compound has to have a phosphate group.
5. Lipases - Lipases include esterases and phospholipiases that act on lipids to produce
acids and alcohol
6. Sulphatases - Sulphatases are enzymes that act on organic compounds to release
sulphates
FUNCTIONS OF LYSOSOME
 Lysosomes are membrane-bound organelles that function as the "stomachs / digestive
organ" of eukaryotic cells. Cells transport material into lysosomes, the material is
digested by the enzymes, and the digested molecules are moved back into
the cytosol for use by the cell. Both extracellular materials brought into the cell by
endocytosis and obsolete intracellular materials are degraded in the lysosome.
 Metamorphosis, autolysis /autophagy, phagocytosis, Heteropgagy, developmental
function are coordinated by cell organelle called lysosome, due to lytic enzyymes.
 They help in intracellular digestion of larger macromolecules, where the enzymes which
are present in lysozyme degrade the larger macromolecules into smaller molecules.
 They also help in autolysis of unwanted organelles.
 They also help in secretion, plasma membrane repair, cell signaling, and energy
metabolism.

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Note:
1. Lysosomes cannot digest themselves - Most of the proteins present in its membrane
contain high amounts of carbohydrate-sugar groups. Because of the present of these
groups, digestive enzymes are unable to digest the proteins present on the membrane.
2. Lysosomal Storage Diseases: Some inherited metabolic disorders can cause defects in the
proper functioning of lysosomes. These disorders are called lysosomal storage diseases, or
LSDs. There are around 40 different LSDs.