Protein Digestion, Lysosomes Flashcards
Where do amino acids come from?
- Degradation of proteins
2. Synthesis of AAs from glycolytic or TCA intermediates (only 10 AAs can be made this way, the rest come from our diet)
List 3 ways that proteins are degraded to attain AAs
- Ubiquitin/Proteasome System
- Digestive Enzymes
When proteins are degraded, what happens to the nitrogen in AAs?
Nitrogen in AAs can be recycled, but excess Nitrogen is excreted
True or False: Because we excrete excess Nitrogen, we need a consistent intake of Nitrogen from our diet.
Name 3 digestive enzymes (in the zymogen form)
(also proelastase and procarboxypeptidase)
What organ(s) release digestive enzymes?
Pancreas and stomach
True or False: Digestive enzymes are stored as inactive zymogens so they do not degrade our own proteins
Which cells secrete pepsinogen, and where is it secreted into?
Chief cells release pepsinogen in the stomach
Discuss the structure of inactive pepsinogen and what low pH does to the zymogen
- Inactive pepsinogen has an N-terminal segment blocking the active site
- When pepsinogen is exposed to low pH, it undergoes conformational change and auto-cleavage to form Pepsin
- at low pH, the electrostatic interactions between the N terminal segment and the rest of the protein are destabilized so now the active site is exposed
What organ releases serine proteases (trypsin, chymotrypsin, elastase, carboxypeptidase)?
What is the optimal pH of the serine proteases to be in?
Name the serine protease that is anchored to the outer membrane of small intestinal epithelial cells
What is the function of enteropeptidase?
It cleaves trypsinogen to activate trypsin
True or False: When trypsinogen is cleaved into typsin, trypsin can further activate trypsinogen to convert into trypsin
True or False: When trypsin is activated, it can activate chymotrypsinogen, proelastase, and procarboxypeptidase into their active forms
True (known as cascade of proteolytic cleavages)
_____ _____ _____ is stored along with zymogens inside the pancreas.
Pancreatic Trypsin Inhibitor (PTI)
What AA does PTI have that allows it to bind closely to trypsin?
True or False: Enteropeptidase cleaves a bond between Lysine and Isoleucine