LECTURE 6 - MEMBRANOUS ORGANELLES: LYSOSOMES AND PEROXISOMES Flashcards
What is the structure of Lysosomes?
- Lysosomes are membrane-bound cells organelles
- Size varying from 0.1 – 1.2 μm.
How can Lysosomes be visualized?
- Using a light microscope
- After staining with toluidine blue and after special histochemical procedures
Why does histochemical visualization work with lysosomes?
- As it reveals the location of acid phosphates in lysosomes. (marker enzymes)
What is the ideal pH for Acid Hydrolases in Lysosomes?
4.5 to 5
with activation proteolytic cleavage
What are the acid hydrolases found in Lysosomes?
Proteases
Nucleases
Glycosidases
Lipases
Phospholipases
Phosphatases
Sulfatases
What are the 3 structural lysosomes proteins?
- Lysosome-associated membrane proteins (LAMPs)
- Lysosomal membrane glycoproteins (LGPs)
- Lysosomal Integral Membrane Proteins (LIMPs)
What is the structure of the Lysosomes membrane proteins? And the purpose of the structure?
- Highly glycosylated - which helps protect them from lysosomes proteases in the lumen
- Transport proteins - transport the final products of digestion to the cytoplasm.
- Vacuolar H+ ATPase in the membrane - to use the energy of ATP hydrolysis to pump H+ into the cytoplasm to make acidic
What are the pathways of delivering material for intracellular digestion in lysosomes for Extracellular Large Particles?
- Extracellular particles (i.e., Bacteria, cell debris, and other foreign materials) are engulfed through phagocytosis
What is the pathway for Extracellular small particles in the lysosomes?
Extracellular small particles (plasma membrane, proteins) are internalized by pinocytosis and receptor-mediated endocytosis
What is the pathway for intracellular particles in the lysosomes?
Intracellular particles (organelles, cytoplasmic proteins) are isolated from the cytoplasmic matrix by endoplasmic reticulum membranes
There are transported to lysosomes and degraded in a process called autophagy.
Explains the process of Autophagy?
- Induction by activation and inactivation of signaling molecules (mTOR Complex 1)
- Nucleation and extension of delimiting membrane into a crescent-shaped cup
- Closure of the membrane cup around the target to form a sealed double membrane-enclosed autophagosome
- Fusion of autophagosome with lysosomes, catalyzed by SNAREs
- Digestion of the inner membrane and lumenal contents of the autophagosomes
What is the residual body?
How long does it remain in the cell?
These are debris-filled vacuoles produced after the hydrolytic breakdown of the contents of the lysosomes.
These remain for the entire life of the cells.
How are lysosomal storage diseases caused?
- Absence of certain lysosomal enzymes causes pathologic accumulation of undigested substrate in residual bodies
How are lysosomal hydrolases recognized and selected in the TGN with the required accuracy?
- MG6 groups are added exclusively to the N-linked oligosaccharides of the soluble lysosomal enzymes as they pass through the lumen of the cis Golgi network
- Transmembrane M6P receptor proteins, present in the TGN recognize the M6P groups and bind to the lysosomal hydrolases on the lumenal side of the membrane and adaptor proteins in assembling clathrin coats on the cytosolic side.
- M6P proteins bind to M6P at pH 6.5-6.7 in the TGN lumen and release it at pH 6, which is the pH in the lumen of endosomes.
- After the receptor is delivered, the lysosomal hydrolases dissociate from the M6P receptors, which are retrieved into transport vesicles that bud from endosomes.
What are the examples of Lysosomal storage diseases?
Hurler Syndrome
McArdle Syndrome
Tay-Sachs
Gaucher
I-cell diseases
