Consider the membrane vesicle containing a protein oriented with its head in the
ID: 206223 • Letter: C
Question
Consider the membrane vesicle containing a protein oriented with its head in the outside monolayer (see picture). The vesicle can be microinjected into the cell. If the vesicle fuses with the membrane listed below, what would be the resulting orientation of the vesicle proteins? Explain, using drawing if needed. Assume that the fusion occurs with conservation of the membrane asymmetry that already exists.
a) injection into cytoplasm before fusion with plasmalemma
b) injection into ER lumen then found in first Golgi cisterna
Explanation / Answer
Membrane vescicle injected into the cytoplasm is brought into close proximity with the plasmamembrane. At critical distance hydrophilic lipid head group of one membrane merges with the opposite membrane.
These vesicles are first docked with GTP binding protein, vescicles are mobilised and attach to presynaptic plasma membrane. Later calcium ions trigger the reaction that catalyse fusion with the membrane.
b)Protein vescicle injected into lumen of ER undergoes further processing catalysed by different glycosyl transferase enzymes and it takes place in golgi cisternae. And these modified glycolipid glycoprotein packed vesicles are processed into lysosomes. All three cell organelles function in coordinated manner and are therefore called as endomembrane system.
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