2. Short response (6pts each, 2 sentences MAX) A. The structure of ATP synthase

Question

2. Short response (6pts each, 2 sentences MAX) A. The structure of ATP synthase in mitochondria is remarkably similar to that of the V-ATPase found in lysosomes. How is it that the former generates ATP while the latter hydrolyzes it? B. Please describe two examples of roles that pH plays in organelle function or in protein transport through the endomembrane system. C. Please provide two similarities and two differences in the molecular mechanisms of how proteins are transported into the ER and into the nucleus. D. What phenomenon are the vesicle transport and cisternal maturation models proposed to explain, and how does this contribute to the proper functioning of the Golgi apparatus?

Explanation / Answer

Both ATP synthase as well as V ATPase are evolutionarily conserved and are considered polar opposite to each other in terms of function. ATP synthase is a proton channel that synthesises energy/ATP from proton gradient whereas V TY0E ATPases are proton pumps that generated proton gradient upon ATP hydrolysis . Although structurally similar, but when we get into the tertiary structures/secondary structures of these proteins , we encounter structural differences that contribute to this function . Also conformational differences between them lead them to have individuality in their function .

B. The pH of extracellular region is mostly neutral. When a protein needs to take the endomembrane system, pH varies when it comes to early endosome to late endosomes (pH 5.5-6). When pH changes receptor -ligand/protein interaction is affected and one of those proteins get recycled back to their location within the cell.Also lysosome has much lower pH where many enzymes are provided an ideal environment for lysosomal degradation .

C. Both require specific signal peptides for their localisation. Both processes require several adaptor and import proteins to help in proper localisation

Differences : Proteins that come in through ER will have post translational modifications like glycosylation/fucosylation whereas nuclear localised proteins may or may not need those modifications for proper trafficking. All membrane proteins go through ER and later may be localised to diffrrend parts of the cell.

D. Vesicular transport is a phenomenon in which vesicles co tribute to the trafficking of several proteins in a closed environment for the specific protein to be transported to its destination . Cisternal progression is a dynamic phenomenon in which an enzyme when trafficked from ER to golgi the enzyme moves from the cis face of golgi to the trans face of golgi and that contributes to the overall functioning of golgi and it's membrane integrity.

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