ID #2458

1) What's the difference between an early and late endosome? Is it just the pH? 2) It becomes a lysosome once the acid hydrolase enzymes enter, correct? 3) What kinds of things are broken down in the lysosome? The book says it takes in material from the outside of the cell. What's the point of bringing in stuff from the outside if it's just going to be broken down? Is it the 'parts' that are needed and not really what is actually being brought in? 4) When we talked about proteins going from ER > golgi > lysosome, thats for the creation of proteins to function in the lysosome and not be broken down?

1) Yes, pH is one of the differences between an early and late endosome, but it is not the only difference. Early endosomes have pH pumps but do not have acid hydrolases yet. Acid hydrolases are delivered to late endosomes. 
2)Once acid hydrolases are delivered to a late endosome, it can start degrading things (although not at the most efficient levels since the pH is still too high for optimal activity of the acid hydrolases). In that regard it acts like a lysosome, but also keep in mind the characteristics of a mature lysosome: lower pH (4.5-5) and the the mannose-6-phosphate receptors have already been recycled back to the Golgi apparatus. 
3) Lysosomes break down organic molecules- proteins, polysaccharides, lipids, and nucleic acids. A macrophage is a type of cell that is part of the immune system. Macrophages will engulf potential threats to the immune system- e.g. certain bacteria. A bacterial cell engulfed by a macrophage will ultimately be degraded by lysosomes. That is just one example of why material is brought in from outside of a cell. 
4) Yes, that was describing how acid hydrolases are brought to their final destination in a lysosome. 

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