Lysosomes
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In what cells are lysosomes found?
Most except RBCs
How are macromolecules delivered to lysosomes?
By endocytosis and autophagy
What enzyme do lysosomes contain?
Hydrolases
How is lysosomal pH maintained?
Vacuolar proton pump, to keep acidic pH optima
Where do lysosomes transport the products of degradation to?
Cytosol
Material destined for degradation is delivered by what 3 pathways
Phagocytosis, autophagy and endocytosis
What is endocytosis materia
Extracellular material and plasma membrane proteins
What is autophagy material
Material from cytosol and whole cytoplasmic organelles
What are phagocytosis material
Large extracellular particulate species like microbes
What is autophagy as a process?
Constitutive process removing cytoplasmic components, enchances by cell starvation
What is macroautophagy
A type of autophagy, removes old organelles, aggregates of proteins and long-lived proteins by autophagasome. It fuses with lysosome
Lysosome involvement in apoptosis
Increased permeability of lysosomal membrane, release of lysosomal proteases called cathepsins into cytosol
Lysosomes in plasma membrane repair
Lysosomes act as a reserve membrane to repair holes, triggered by influx of Ca2+ into cell detected by lysosomal membrane protein synaptotagmin 7
What is I-cell disease?
Autosomal recessive disorder which causes fromation of intracellular inclusions
What mutation is I-cell disease from?
GNPTA which encodes enzyme N-acetylglucosimine-1-phosphotransferase
What is mucolipidosis type II otherwise called
I-cell disease
I-cell disease features
Facial and skeletal abnormalities Severe impairment of mental abilities and movement Heart failure in first ten years
Is there a cure for I-cell disease
No
Molecular basis for I-cell disease
Reduced intracellular levels of lysosomal hydrolases. No modified by N-acetylglucosamine-1-phosphotransferases hydrolases, so aren’t recognised by M6P receptors and are secreted
What is N-acetylglucosamine-1-phosphotransferase is involved in?
Modification of mannosylated glucans attatched to newly synthesised lysosomal hydrolases to produce M6P tag
What is Pompe disease caused by?
Autosomal recessive mutations in gene that encodes the lysosmal hydrolase lysosomal acid alpha-D-glucosidase
Clinical symptoms of Pompe disease
Progressive cardiac and skeletal myopathy Infantile- disease occurs in first year
What does alpha-D-glucosidase do?
Lysosomal alpha-D-glucosidase cleaves glycogen into glucose that can be transported into the cytosol
Molecular basis of pompe disease
Deficiency in lysosomal ⍺-D-glucosidase causes the abnormal accumulation of glycogen in cells and the resultant symptoms of the disease