Overview of Protein Biochemistry Flashcards
What are four ways to categorize amino acids?
CHEMICAL PROPERTIES: Acid/Base, Polar/Nonpolar
BODY’S ABILITY TO SYNTHESIZE THEM: Essential, Nonessential, Conditionally Essential
CHEMISTY/STRUCTURE OF SIDE CHAIN: Sulfur containing, Nitrogen containing, Branched Chain, Aromatic rings
ENERGY METABOLISM: Glucogenic, Ketogenic
Name four important post-translationally modified amino acids
Hydroxy-Proline
Hydroxy-Lysine
gamma-carboxyglutamate
Ornithine
How are dietary proteins broken down in the gut?
Peptidase enzymes degrade dietary proteins. There are many different peptidases present that have different specificities for peptide bonds and preferentially target those bonds. These peptidases are activated in the gut lumen and work sequentially to break down peptide chains into component amino acids.
What are the two pathways by which intracellular proteins are broken down?
Lysosomes and ubiquination
How are NH2 groups removed from or added to carbon skeletons of amino acids?
In Transamination reactions. In the catabolic reaction, an amino acid donates an NH2 group to α ketoglutarate to produce L glutamate and an α keto acid. The enzyme that catalyzes this reaction is an aminotransferase. Different aminotransferases have different specificities for different amino acids. The nitrogen that has been accepted by α ketoglutarate with the production of glutamate can then be released as NH3 with the regeneration of α ketoglutarate. This ammonia is toxic and needs to leave the body. It does so through the process of urea synthesis.
Briefly describe the urea cycle
The ammonia produced in the transamination reaction is converted to carbamoyl phosphate (H2N-C=O-PO3), which then acquires another NH2 group from aspartate to eventually form urea (H2N-C=O-NH2) via L-arginine.
How does nitrogen eventually leave the body?
Via urea in “urine urea nitrogen”. Urinary urea nitrogen is thus a marker of amino acid catabolism and oxidation. A minor pathway for nitrogen removal involves arginine and the production of nitric oxide.
What is the importance of glutamine?
Glutamine contains two nitrogen atoms and carries nitrogen to the liver where it is donated to glutamate and from there to a-ketoglutarate. The conversion of glutamate to a-ketoglutarate is accomplished by glutamate dehydrogenase and is the second key, regulated step in protein catabolism.
What are the two sulfur containing AA and what are four reasons they are important?
Cysteine and Methionine
1 - Cysteine forms disulfide bridges in protein structures
2 - S-adenosylmethionine (SAM) is an energy source for reactions and a methyl donor.
3 - SAM is a precursor for homocysteine which functions in wound healing, vascular disease, and Folate/B12 metabolism
4 - Cysteine is a component of the trip-peptide Glutathione, which is a redox buffer and protective against free radicals
Why are glucogenic, ketogenic, and branched chain AA important?
They are involved in gluconeogensis or ketone production and are important in those pathways. Branched chain AA metabolism requires special enzymes and their products enter the TCA cycle. Defects in these enzymes lead to Maple Syrup Urine Disease.
What are the aromatic AA, and why are they important?
Tryptophan, phenylalanine, and tyrosine.
These amino acids are used as precursors for a wide variety of important products including serotonin, niacin, dopamine, epinephrine, norepinephrine, tetrahydrobiopterin, and thyroid hormone.
