Urea Cycle Flashcards
What are proteins made of?
Proteins are polymers of amino acids.
How are amino acids obtained from proteins?
By acid, alkali, or enzymatic hydrolysis.
What are the classifications of amino acids?
Chemical, Nutritional, and Metabolic.
Where are free amino acids found in the body?
In cells, blood, and extracellular fluid.
What are the sources of the amino acid pool?
1) Endogenous protein degradation
2) diatary ptns
3) anabolism of non essential aka
How is the amino acid pool depleted?
1) Synthesis of body protein
2) catabolism
3) anabolism of NPNCs
What is protein turnover?
The balance of protein synthesis and degradation (~300–400g/day).
What does a negative nitrogen balance indicate?
Tissue destruction.
What are the two major protein degradation systems?
1) ATP-dependent ubiquitin-proteasome system
2) ATP-independent lysosomal degradation
What is the function of the ubiquitin–proteasome pathway?
Selective degradation of damaged or misfolded proteins.
Key enzymes in ubiquitination?
E1 (activates), E2 (conjugates), E3 (ligates).
What is the role of the proteasome?
Recognizes, unfolds, and degrades polyubiquitinated proteins.
What mechanism is used for extracellular protein degradation?
Receptor-mediated endocytosis (heterophagy).
What is autophagy?
Non-selective degradation of intracellular proteins.
What are the two phases of amino acid catabolism?
1) Removal of the α-amino group
2) Breakdown of the remaining carbon skeleton
What happens in transamination?
Transfer of an amino group from an amino acid to an α-keto acid.
What coenzyme is required for aminotransferases?
Pyridoxal phosphate (vitamin B6 derivative).
Which two enzymes are key aminotransferases?
ALT (Alanine aminotransferase) and AST (Aspartate aminotransferase).
What is the role of α-ketoglutarate in transamination?
It accepts amino groups, forming glutamate.
What makes ALT and AST clinically significant?
Elevated plasma levels indicate liver or muscle damage.
What enzyme catalyzes oxidative deamination of glutamate?
Glutamate dehydrogenase (GDH).
What coenzymes does GDH use?
NAD⁺ or NADPH.
What regulates GDH activity allosterically?
Inhibited by GTP, activated by ADP.
What are the two ammonia transport mechanisms in the body?
1) As glutamine (via glutamine synthetase → glutaminase)
2) As alanine (via glucose–alanine cycle)
