Protein_Metabolism_Brainscape_Flashcards
What do amino acids and nucleotides contain that carbohydrates and fats don’t?
Nitrogen
Where does nitrogen in our diet ultimately come from?
From nitrogen fixing bacteria (diazotrophs) that convert atmospheric nitrogen
Why is nitrogen difficult to capture from the atmosphere?
Because nitrogen (N2) is very unreactive due to its triple bond
What enzyme is required for nitrogen fixation?
Nitrogenase
Why is nitrogenase sensitive to oxygen?
It is inactivated by oxygen
How do nitrogen-fixing bacteria deal with oxygen?
Live anaerobically or use mechanisms like leghemoglobin to bind oxygen
What molecule plays a central role in nitrogen flow after fixation?
Glutamate
Which amino acids are found in much higher concentrations in cells?
Alanine, glutamine, glutamate, and aspartate
What is transamination?
Transfer of amino groups between molecules without nitrogen loss
What cofactor is required for aminotransferase enzymes?
Pyridoxal phosphate (PLP), made from vitamin B6
What does the presence of aminotransferases in plasma indicate?
Cell damage, especially liver damage
Which two aminotransferases are useful for diagnosing liver disease?
AST (aspartate aminotransferase) and ALT (alanine aminotransferase)
What organisms rely heavily on amino acid oxidation for energy?
Carnivores
When do amino acids undergo oxidative catabolism?
Excess dietary intake, protein turnover, or energy demand during starvation/diabetes
Which enzymes digest proteins in the stomach and small intestine?
Pepsin (stomach), trypsin and chymotrypsin (small intestine), aminopeptidases and carboxypeptidases A & B
What is the endpoint of protein digestion?
Free amino acids
Which amino acid is central to nitrogen removal?
Glutamate
In what form do terrestrial vertebrates excrete nitrogen?
Urea
In what form do birds and reptiles excrete nitrogen?
Uric acid
How is ammonia safely transported in blood?
As glutamine
What is the glucose-alanine cycle?
Transport of nitrogen from muscle to liver as alanine
Why are alanine and glutamine used to transport nitrogen?
They are uncharged and can cross membranes more easily than glutamate
What enzyme catalyzes oxidative deamination of glutamate?
Glutamate dehydrogenase
What is the first nitrogen-acquiring step in the urea cycle?
Synthesis of carbamoyl phosphate
