I-Cell Disease (Golgi)
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What are the clinical findings of I-cell disease?
*Increased lysosomal enzyme in ECM Death by age 5 (heart failure) Poor bone development and limited joint mobility Irregular ossification Neurological deterioration
True or false, the Golgi is part of the RER?
True; ER-built molecules and membranes move to Golgi
True or false, the Golgi is poorly developed in metabolically active cells and secretory cells?
False; it is WELL developed in those cells
How does the Golgi appear under a microscope?
Light microscope=hard to see; pale patch close to nucleus EM=series of 5-7 flattened membrane-bound saccules. Each sac contains a cisternae
What are the 4 functional compartments Golgi cisternae divide into?
“cis” - ‘forming face’ faces ER; modification site of newly synthesized proteins and lipids “medial”- saccules* middle of Golgi; receives vesicles that have pinched off cis sac “trans” - ‘releasing face’; concave, faces away from ER; vesicles released to cytoplasm “trans Golgi network” - accumulation of budded trans vesicles;
Golgi is rich in the enzyme glycosyltransferase. What does this enzyme do? Which direction does it face?
Faces cisternal sides of sacs; Adds or modifies sugar chains to create glycoproteins and glycolipids
What are the three main functions of Golgi?
Lysosome formation, secretory vesicle formation, plasma membrane renewal
Lysosomes contain an array of digestive enzymes of a class known as a ….
Hydrolase
In the “cis” golgi, the mannose (sugar chain hooked to hydrolase) is capped with phosphates by an enzyme called…
glucosamine phophotransferase
What are the Golgi membrane receptors called that gather the hydrolyses from the “trans” sac to TGN?
mannose-6-phosphate receptors (M6P)
True or False: Without a mannose phosphate flag, the leftover proteins travel to a nearby mitochondria.
False; If not separated into a lysosome by way of phosphorylated mannose oligosaccharide flags, the TGN produces vesicles destined for exocytosis. Thus, they travel to plasma membrane
What are the two types of exocytosis from the Golgi?
Constitutive = w/o delay Regulated = vesicle binds to cytoskeleton and is released after stimulation (by Ca++)
I-Cell disease is known to be due to a failure of …?
Glucosamine Phosphotransferase = cannot phosphorylate hydrolases (causes 2 things) 1-lysosomal enzymes sent to ECM (which mobilize GAGs into urine) 2-anything brought into cell by endocytosis cannot be broken down by lysosomes
I-Cell disease is a failure of what part of the cell?
Golgi; golgi is incapable of sorting out proteins sent from the ER, and this is b/c ER sends a bad enzyme used in early sorting process