1. Pancreatic cells produce digestive enzymes that are capable of digesting prot
ID: 57070 • Letter: 1
Question
1. Pancreatic cells produce digestive enzymes that are capable of digesting proteins, carbohydrates, lipids, and other molecules. Why then don’t these enzymes digest the pancreatic cells themselves?
2. True or False: The first cells of “early Earth” were surrounded by a membrane composed largely of lipids synthesized by protein-catalyzed reactions. Explain.
3. Many cell types are busy endocytosing particulate and/or soluble material. The formation of endosomes (vacuoles formed by endocytosis) requires the use of cell membrane. It would take too much energy for cells to continually synthesize new plasma membrane to replace the membrane that is used to form endosomes. Yet the plasma membrane of cells that are continually endocytosing material does not become smaller and smaller. So, given your understanding of the endomembrane system, where does the membrane come from?
Explanation / Answer
1. Digestive enzymes are secreted in an inactive form. They need to be activated by various other enzymes or chemicals present in the digestive tract. And they are highly specific so they selectively digest the molecules, which do not include the cell membranes of the pancreatic cells.
2. The given statement is false, because the most primitive cell on the earth did not contain proteins to carryout chemical reaction. The first molecule formed was RNA, which has enzyme like activity. Probably the RNA having enzymatic activity catalyzed such reactions.
3. The membrane lipids are synthesized in the Golgi complex. Membranes of vesicle derived from the Golgi complex or endosomes are recycled back into the plasma membrane, thus retains the size of the cell membrane.
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