Protein Biochemistry I Flashcards
What is the structure of collagen and how does achieve this structure?
Collagen is a triple stranded helix, the most abundant triple stranded helix in the body. It achieves this structure through the post-translational modification of proline and lysine to hydroxy-proline and hydroxy-lysine.
What enzymes modify proline and lysine post-translation?
Proline is modified by prolyl-hydroxylase to hydroxy-proline.
Lysine is modified by lysyl-hydroxylase to hydroxy-lysine.
What are hydroxy-proline and hydroxy-lysine’s roles in collagen?
Hydroxy-proline increases collagen strength via H-bonds.
Hydroxy-lysine creates interchain cross-links.
What role does Vitamin C play in collagen formation?
Vitamin C is a coenzyme for lysyl-hydroxylase. A lack of vitamin C decreases the creation of hydroxy-lysine, which results in less cross linkage of collagen helixes.
What is the product of the post-translational modification of Glutamine and what enzyme achieves this?
G-glytamyl carboxylase converts Glu to gamma-carboxyglutamate (Gla). Gla is involved in the chelation of Calcium.
What role does Vitamin K play in calcium chelation?
Vitamin K is a cofactor/coenzyme required for G-glytamyl carboxylase creation of Gla, which in turn chelates calcium.
What is the ubiquitin-proteasome system for protein degradation?
The ubiquitin-proteasome system is an ATP-dependent system that crosslinks a targeted protein with ubiquitin. The ubiquitinated protein is then moved into a proteasome where it is degraded by proteolytic activities.
What is the lysosome pathway for protein degradation?
The lysosome pathway is ATP-independent and used to engulf extracellular proteins or live pathogens. Proteins are broken down by acid hydrolysis and other lysosomal proteins like cathepsins.
What is the general sequence of protein degradation by proteases?
Multiple proteases are used to break down proteins into individual AA. These proteases are initially proenzymes and must be cleaved to be activated. Pepsinogen is cleaved by HCl in the stomach and initiates peptide breakdown. Trypsinogen is the master enzyme of the intestines. It is cleaved by enteropeptidase to trypsin, which then cleaves all of the other protease zymogens, including chymotrypsinogen and procarboxypeptidases.
What are the actions of aminotransferases?
Aminotransferases transfer amine groups and convert one a-keto acid to its corresponding amino acid in exchange for converting another amino acid into an a-keto acid. These are reversible reactions with Keq ~ 1. There are 100’s of aminotransferases, each specific to only a few amino acids. They may also be used in protein degradation to transfer amine groups into the Urea cycle via Asp and ammonia.
What are two special aminotransferases?
Alanine aminotransferase (Alt) Aspartate aminotransferase (Ast) Very important liver function enzymes
What role does Vitamin B6 play in protein metabolism?
Pyridoxal phosphate (PLP) is a derivative of Vitamin B6 and is a cofactor for aminotransferases. It is used to “hold” or transfer the amine groups.
What is the purpose of the Urea cycle?
The eliminate ammonia by forming less toxic compounds.
What are the chemical inputs to the urea cycle?
3 ATP, 1 HCO3, 1 NH4, and 1 aspartate, ornithine (recycled)
What are the products of the urea cycle?
2 ADP, 1 AMP, 2 Pi, 1 PPi, 1 fumarate, 1 Urea, ornithine (recycled)
