24 Questions
What is the size range of lysosomes?
0.5 - 1 μm in diameter
Who first discovered lysosomes?
Christian de Duve
In which type of cells are lysosomes not found?
Erythrocytes
What is the function of acid hydrolases in lysosomes?
To control digestion of macromolecules
Which organelle is formed when a phagosome is fused with a primary lysosome?
Phagolysosome
What accumulates in neurons, heart muscle cells, and liver cells of aging individuals, causing brown degeneration?
Lipofuscin pigment
What is the result of defective acid hydrolases causing the accumulation of undigested substrates?
Lysosomal storage diseases
Which enzyme defect causes Glycocerebrosides to accumulate in the CNS and spleen, leading to Gaucher’s disease?
Glycocerebrosidase
What enzyme defect leads to the accumulation of Sphingomyelin and Cholesterol in the CNS, spleen, and liver, causing Niemann-pick disease?
Sphingomyelinase
Which enzyme defect causes the accumulation of Gangliosides in the CNS, leading to Tay-Sachs disease?
Hexaminidase
What marker cannot be added to lysosomal hydrolases in I-cell disease due to a defect in the GlcNAcphophotranspherase enzyme?
M6P marker
What happens to the enzymes in I-cell disease as a result of the defect in GlcNAcphophotranspherase?
They are released to the exterior of the cell
What is the pH range at which lysosomal enzymes are active?
pH 4.5-5
Where are lysosomal hydrolases synthesized?
Endoplasmic reticulum (ER)
What prevents the uncontrolled digestion of the cytosol by lysosomal enzymes?
Lysosomal membrane
Which organelle recognizes the unique marker, mannoz-6phosphate, on lysosomal proteins?
Trans-Golgi network
What is the function of autophagy in cellular processes?
Targeting senescent organelles for degradation
What type of cells engulf foreign material through phagocytosis?
Macrophages and neutrophils
Where are lysosomal hydrolases glycosylated and modified?
ER and Golgi
What do lysosomes mediate the breakdown of?
Intra- and extracellular materials
What happens to lysosomal enzymes at an acidic pH?
They dissociate from the M6P receptors
What type of fusion forms secondary lysosomes?
Primary lysosomes and late endosomes
What is the role of lysosomes in the production of nutrients for the cell?
Mediating the breakdown of materials
What is the function of lysosomal membrane transport proteins?
Carrying final digestion products to the cytosol
Study Notes
Lysosomes: Key Players in Cellular Waste Management
- Lysosomes contain around 50 different hydrolytic enzymes, which are active at an acidic pH (4.5-5).
- Lysosomal enzymes are resistant to proteases and peptidases.
- The lysosomal membrane prevents the uncontrolled digestion of the cytosol by keeping the digestive enzymes out, even if it breaks down.
- Lysosomal membranes contain transport proteins that carry the final digestion products to the cytosol for reuse.
- Primary lysosomes fuse with late endosomes to form secondary lysosomes.
- Lysosomal proteins carry a unique marker, mannoz-6phosphate, added in the cis-Golgi network, which is recognized by M6P-receptor proteins in the trans-Golgi network.
- Acidic pH causes the lysosomal enzymes to dissociate from the M6P receptors.
- Lysosomal hydrolases are synthesized in the ER, glycosylated in the ER and Golgi, and modified in the cis Golgi by the addition of M6P markers.
- Lysosomes mediate the breakdown of intra- and extracellular materials, production of nutrients for the cell, and destruction of phagocytosed microorganisms.
- Materials are delivered to lysosomes through three pathways: endocytosis, phagocytosis, and autophagy.
- Autophagy selectively targets senescent organelles for degradation and plays a role in cell survival, development, and health.
- Phagocytosis is found in specialized cells like macrophages and neutrophils, which engulf foreign material.
Test your knowledge of lysosomes with this quiz on their structure, function, and role in cellular waste management. Explore topics such as lysosomal enzymes, membrane structure, fusion processes with endosomes, and the pathways through which materials are delivered to lysosomes.
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