Describe the biogenesis and function of lysosomes. What is the function of lysos

Question

Describe the biogenesis and function of lysosomes. What is the function of lysosomes? Why must their contents be compartmentalized? Why must the lumen of lysosomes be regulated at an acidic pH? How are newly synthesized hydrolases sorted from other proteins and targeted to lysosomes? Describe the role of lysosomes in some specialized cell types. Trace the movement of a phagocytosed particle in a phagocytic cell. What is the difference between a heterophagic and an autophagic lysosome? Discuss the processes of autophagy and extracellular digestion, and outline their roles in specialized cells.

Explanation / Answer

Answer:

a. Lysosomes are membrane bound organelles containing more than acid hydrolases and function in the degradation of macromolecules delivered via endocytic, phagocytic, and autophagic pathways.

Lysosome biogenesis:

i. Lysosomal hydrolases are synthesized in ER and traffic to Golgi

ii. Golgi recognizes hydrolases & covalently adds oligosaccharide to the hydrolase

iii. Oligosaccharide is modifed to expose M6P residues in trans Golgi network (TGN)

iv. TGN has M6P receptors that bind M6P residues on hydrolases and concentrate these hydrolases in specific areas of TGN that creates primary lysosomes

v. Fusion of primary lysosome with endosome, phagosome, autophagosome gives rise to mature lysosome

b. Lysosomes are called suicidal bags which destroy the worn out cellular parts and the digestive enzymes degrade food stuffs and infectious agents.

c. Comparmentalization seals the cellular digestion in lysosomes and prevents an unwanted auto-digestion of other organelles within cell. A common processes that accompany the disruption of some of the compartments (like spilling the content of lysosomes or mitochondria) are necrosis or activation of apoptosis (the process of programmed cell death).

d. Lysosomes must maintain an acidic luminal pH to activate hydrolytic enzymes and degrade internalized macromolecules. Acidification requires the vacuolar-type H+-ATPase to pump protons into the lumen and a counterion flux to neutralize the membrane potential created by proton accumulation.

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