ROLE OF LYSOSOMES AS HYDROLYTIC ACTIVITY OF

ENZYMES

ROLE OF LYSOSOMES AS HYDROLYTIC ACTIVITY OF

ENZYMES

Introduction of Lysosomes

Structure of Lysosomes

Formation of Primary Lysosomes

Formation of Secondary Lysosomes

Lysosomes are the principal sites of intracellular digestion

Multiple Pathways Deliver Material to Lysosomes

CONTENTS

Functions of Lysosomes

Steps in Autophagy

Storage Diseases

cytoplasmic organelles

Structure is different from other organelles

Isolated by Duve in 1949

Lyso soma

Splitting bodySO they are concerned with the breaking activities.

✿ Bounded by a single membrane. This membrane forms a simple sac.

✿This sac contains several hydrolytic enzymes like acid phosphatases.

Enzymes of lysosomes are synthesized by ribosomes present in RER transferred to Golgi apparatus These enzymes are further processed in the Golgi apparatus.Budded off as Golgi vesicles primary lysosomes.

Secondary lysosomes are formed by two method

☞The foreign object fuses with the primary lysosomes to form secondary lysosomes.

☞In lysosomes ,enzymes digest the food particles.

☞ (A) Lysosomes protect the body against the invading organisms.

☞Engulf the food particles.

• Some time, under some abnormal conditions like starvation or normal physiological conditions, the primary lysosomes engulf the parts of cell.

• It digests these parts and release energy.

• The lysosomes which eat parts of its own cells are called autophagosomes.

• These autophagosomes are also called secondary lysosomes

• Membrane-enclosed compartment filled with soluble hydrolytic enzymes that control intracellular digestion of macromolecules.

• Containing about 40 types of hydrolytic enzymes including

• Protease that digest proteins• Nuclease that digest nucleic acids

Lysosomes are the intracellular Digestion

• Lipase that digest lipids

• Phospholipase that digest phospholipids

• All are hydrolases.

• For optimal activity, they need to be activated by proteolytic cleavage and require environment, which the lysosome provides by maintaining an pH of about 4.5-5.0 in its interior .

• Contents of the cytosol are doubly protected by the cell’s own digestive system:

•

• The membrane of the lysosome keeps the digestive enzymes out of the cytosol, but even if they leak out, they can do little damage at he cytosolic pH about 7.2

• Like all other intracellular organelles, the lysosome contains a unique collection of enzymes, it also has a unique surrounding membrane.

• Most of the lysosomal membrane proteins, for example, are unusually highly glycosylated, which helps to protect them from the lysosomal proteases in the lumen.

• Transport proteins in the lysosomal membrane carry the final products of the digestion of macromolecules-such as amino acids, sugars, and nucleotides-to the cytosol, where the cell can either reuse or excrete them.

Auacuolar H ⁺ ATPase in the lysosomal membrane uses the energy of ATP hydrolysis to pump H ⁺ into the lysosome, thereby maintaining the lumen at its acidic pH

The lysosomeal H ⁺ pump belongs to the family of V-type ATPase

Multiple pathway to Deliver Materials to Lysosomes

• AUTO PHAGY:

• oneself to eat• Autophagy is a process of self-eating and

self-degradation. The degradation takes part when the cell content and organelles is consumed by lysosomes

• Cell contains some old, broken parts like old mitochondria.

• The cell produces vesicles called autophagosomes that captures and deliver cytoplasmic material to lysosomes.

The macromolecules taken up from extracellular fluid by endocytosis. endocytosed molecules are initially delivered in vesicles to small, irregularly shaped intracellular organelles called early endosomes.

• Lysosomes then fuse with endosomes, whereby it transfers it enzymes to breakdown molecules. The broken down molecules are then delivered to the cytoplasm by proteins for later consumption.

• Any foreign object is engulfed by lysosomes

• Broken into digestive pieces.phagocytosis

Phagocytosis

• Lysosomes contain enzymes which can digest the phagocytosed food

• :• Lysosomes also release enzymes for

extracellular digestion.

1) Nucleation and extension of a delimiting membrane into a crescent shaped structure that engulfs a portion of the cytoplasm.

2) Closure of the autophagosomes into a sealed double- membrane –bounded compartment

3) Fusion of the new compartment with lysosomes

• Digestion of the inner membrane of the autophagysome and its contents.

• Several congenital diseases are caused accumulation of certain

substances like glycogen and glycolipids.

These disease caused due to mutation.Affects the lysosomal enzymes.These diseases are caused due to

absence of certain enzymes.

✿

✿ The enzymes which breaks the glycogen into glucose is absent.

✿ So, glycogen is filled in the membranous bound organelles of the cell of the muscles and liver.

Glycogenesis Type II

☞ The enzymes which is involved in the catabolism of lipid is absent.

☞ Cause accumulation of lipids in brain cells

☞ Cause mental retardation

☞ And even death.