Cell Nitrogen Metabolism and Nucleic Acid Metabolism

This set of vocabulary flashcards covers nitrogen metabolism, the urea cycle, amino acid catabolism, and the synthesis and degradation of purines and pyrimidines based on the provided lecture notes.

Endogenous proteins

Proteins that are synthesized inside the cell.

Proteasome

A large barrel-shaped structure that acts as a protein garbage disposal, breaking down ubiquitin-tagged proteins into peptides or amino acids.

De novo synthesis

The formation of nitrogenous bases or amino acids from scratch using simple precursor molecules rather than recycling pre-existing bases.

Salvage pathways

The metabolic processes that recycle pre-existing purine and pyrimidine bases, obtained from normal cell turnover, to synthesize nucleotides.

Gout

A form of inflammatory arthritis caused by the deposition of monosodium urate crystals in the joints due to hyperuricemia.

Essential amino acids

Amino acids that cannot be synthesized by the body or are not synthesized in sufficient quantities, requiring them to be obtained exogenously through the diet.

Non-essential amino acids

Amino acids that the body can synthesize from various precursors or metabolic intermediates.

Conditionally essential amino acids

Amino acids that are normally synthesized by the body but must be obtained from the diet in larger amounts during periods of stress, trauma, growth, or pregnancy, such as Arginine.

Amino acid pool

The collective mixture of amino acids found in the bloodstream and tissues, averaging approximately $100\,\text{g}$ in a stable state.

Transamination

The transfer of an amino group from an amino acid to a ketoacid, typically catalyzed by transaminase using the coenzyme Pyridoxal Phosphate ($PLP$).

Oxidative deamination

The removal of an amino group from an amino acid as free ammonia ($NH_3$), occurring in Phase 1 of amino acid catabolism.

Glucogenic amino acids

Amino acids whose carbon skeletons can be converted into precursors for glucose synthesis, such as pyruvate or Krebs Cycle intermediates.

Ketogenic amino acids

Amino acids whose carbon skeletons feed into precursor molecules for fatty acid synthesis or ketone body formation, specifically Acetyl-CoA or Acetoacetyl-CoA.

Lysine and Leucine

The two amino acids that are categorized as exclusively ketogenic.

Ubiquitin-proteasome Pathway

An energy-dependent ($ATP$-dependent) degradation pathway used primarily for breaking down proteins synthesized within the cell.

Lysosomal Pathway

An energy-independent degradation pathway involving hydrolytic enzymes within lysosomes, typically for proteins absorbed by the cell.

Urea Cycle

A biochemical pathway occurring in the liver that converts toxic ammonia or ammonium ($NH_4^+$) into relatively safe urea for excretion.

N-acetylglutamate

The essential allosteric activator for the enzyme Carbamoyl Phosphate Synthetase I ($CPS\,I$) in the urea cycle.

$5\text{-PhosphoRibosyl-1-PyroPhosphate}$ ($PRPP$)

An important precursor made from Ribose-5-Phosphate that provides the phosphoribose unit for both purine and pyrimidine nucleotide synthesis.

Carbamoyl Phosphate Synthetase I ($CPS\,I$)

An isoenzyme located in the mitochondrial matrix involved in the urea cycle that uses ammonia as a nitrogen source.

Carbamoyl Phosphate Synthetase II ($CPS\,II$)

A cytosolic isoenzyme involved in pyrimidine synthesis that uses the amide group of glutamine as a nitrogen source and is inhibited by $UTP$.

Inosine-5'-Monophosphate ($IMP$)

The precursor molecule for the synthesis of the purine nucleotides Guanosine and Adenosine.

Xanthine oxidase

The enzyme responsible for converting hypoxanthine and xanthine into uric acid during purine catabolism.

Allopurinol

A pharmacological inhibitor of xanthine oxidase used to reduce the production of uric acid.

Lesch-Nyhan Syndrome

An X-linked genetic disorder caused by a deficiency in HGPRT, leading to failed purine salvage and significant hyperuricemia.