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Questions and Answers
Histamine is a vasoconstrictor.
Histamine is a vasoconstrictor.
False (B)
Dopamine is an intermediate in the formation of adrenaline.
Dopamine is an intermediate in the formation of adrenaline.
True (A)
GABA is a vasoconstrictor and a neurohumoral agent in the venoms of wasps.
GABA is a vasoconstrictor and a neurohumoral agent in the venoms of wasps.
False (B)
Transamination involves the transfer of a keto group from a keto-acid to an amino acid.
Transamination involves the transfer of a keto group from a keto-acid to an amino acid.
Glutamate dehydrogenase is a simple enzyme that catalyzes the oxidative deamination of L-glutamate.
Glutamate dehydrogenase is a simple enzyme that catalyzes the oxidative deamination of L-glutamate.
D-Amino acid oxidase is present in the liver, kidney, and brain.
D-Amino acid oxidase is present in the liver, kidney, and brain.
Serine and Threonine are deaminated by specific deaminases in a reaction preceded by hydration.
Serine and Threonine are deaminated by specific deaminases in a reaction preceded by hydration.
The liver is not a major site of nitrogen metabolism in the body.
The liver is not a major site of nitrogen metabolism in the body.
The carbon skeletons produced from amino acids are degraded to form 5 metabolic products.
The carbon skeletons produced from amino acids are degraded to form 5 metabolic products.
Amino acid catabolism begins by adding the amino group.
Amino acid catabolism begins by adding the amino group.
Lysine is a guianidinium ion that is always protonated.
Lysine is a guianidinium ion that is always protonated.
Threonine has one chiral carbon.
Threonine has one chiral carbon.
Asparagine is an amide of glutamic acid.
Asparagine is an amide of glutamic acid.
Leucine is a glycogenic amino acid.
Leucine is a glycogenic amino acid.
Isoleucine is only a ketogenic amino acid.
Isoleucine is only a ketogenic amino acid.
Amino acid molecules in the amino acid pool come only from dietary proteins.
Amino acid molecules in the amino acid pool come only from dietary proteins.
Porphyrin is synthesized from fatty acids.
Porphyrin is synthesized from fatty acids.
A positive nitrogen balance occurs when nitrogen intake equals nitrogen loss.
A positive nitrogen balance occurs when nitrogen intake equals nitrogen loss.
The reaction of deamination involves the removal of the β-amino group from amino acids.
The reaction of deamination involves the removal of the β-amino group from amino acids.
Oxidative deamination is a reversible biochemical reaction.
Oxidative deamination is a reversible biochemical reaction.
Transamination reactions are catalyzed by Oxidase enzymes.
Transamination reactions are catalyzed by Oxidase enzymes.
Lysine is an amino acid that participates in transamination reactions.
Lysine is an amino acid that participates in transamination reactions.
Pyridoxal phosphate (PLP) serves as the cofactor for oxidative deamination reactions.
Pyridoxal phosphate (PLP) serves as the cofactor for oxidative deamination reactions.
Vitamin B6 is derived from pyridoxal phosphate (PLP).
Vitamin B6 is derived from pyridoxal phosphate (PLP).
Ornithine transcarbamoylase is the enzyme responsible for the conversion of citrulline to arginosuccinate.
Ornithine transcarbamoylase is the enzyme responsible for the conversion of citrulline to arginosuccinate.
The urea cycle occurs exclusively in the cytoplasm.
The urea cycle occurs exclusively in the cytoplasm.
Argininosuccinate synthetase is the enzyme responsible for the conversion of citrulline to arginine.
Argininosuccinate synthetase is the enzyme responsible for the conversion of citrulline to arginine.
The urea cycle is activated by N-acetylglutamate.
The urea cycle is activated by N-acetylglutamate.
Pyrophosphatase is involved in the reaction catalyzed by argininosuccinate synthetase.
Pyrophosphatase is involved in the reaction catalyzed by argininosuccinate synthetase.
The enzyme arginase is responsible for the conversion of arginine to ornithine and urea.
The enzyme arginase is responsible for the conversion of arginine to ornithine and urea.
The urea cycle requires four ATP molecules.
The urea cycle requires four ATP molecules.
Ornithine is regenerated at the end of the urea cycle.
Ornithine is regenerated at the end of the urea cycle.
Urea is produced in the kidneys of ureotelic animals.
Urea is produced in the kidneys of ureotelic animals.
Arginase is found in significant amounts in the kidney.
Arginase is found in significant amounts in the kidney.
The net reaction for the urea cycle involves the production of urea and fumarate.
The net reaction for the urea cycle involves the production of urea and fumarate.
Fumarate is a component of the urea cycle.
Fumarate is a component of the urea cycle.
Oxaloacetate can be used in energy generation or converted to glucose or aspartate.
Oxaloacetate can be used in energy generation or converted to glucose or aspartate.
Urea is eliminated in the urine by the liver.
Urea is eliminated in the urine by the liver.
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Study Notes
Amino Acid Classification
- Lysine is a diamino acid, protonated at pH 7.0
- Arginine is a guianidinium ion, always protonated, and the most basic amino acid
Polar Uncharged Amino Acids
- Have polar side groups, are hydrophilic, and can form hydrogen bonds
- Examples: Serine (Ser, S), Threonine (Thr, T), Asparagine (Asn, N), Glutamine (Gln, Q)
Classification of Amino Acids Based on Metabolic Intermediates
- Glycogenic amino acids are catabolized to pyruvate, α-ketoglutarate, succinyl CoA, fumarate, or oxaloacetate
- Examples: Alanine, Asparagine, Aspartate, Arginine, Cysteine, Glutamate, Glutamine, Histidine, Methionine, Proline, Serine, Threonine, and Valine
- Ketogenic amino acids are catabolized to acetyl CoA or acetoacetyl CoA
- Examples: Leucine and Lysine
- Some amino acids are both glycogenic and ketogenic
- Examples: Isoleucine, Phenylalanine, Tryptophan, and Tyrosine
Catabolism of Carbon Chains from Amino Acids
- Complex series of reactions involved in the breakdown of amino acids
- Amino acid molecules are continuously synthesized and degraded
- Amino acid pool is a source of amino acids for various metabolic processes
Nitrogen Balance
- Nitrogen intake (primarily amino acids) equals nitrogen loss in healthy adults
- Positive nitrogen balance occurs in growing children, pregnant women, and recuperating patients
General Reactions of Amino Acids
- Amino acids can be decarboxylated to amines, which have important physiological roles
- Examples: Histidine → Histamine, Dopa → Dopamine, and 5-hydroxy tryptophan → Serotonin
Transamination
- Involves the transfer of an amino group from an amino acid to a keto-acid to form the corresponding amino acid
- Catalyzed by aminotransferases, which require pyridoxal phosphate as a prosthetic group
- Examples: AST and ALT
Oxidative Deamination
- Glutamate dehydrogenase catalyzes the oxidative deamination of L-glutamate to α-ketoglutarate and ammonium
- Occurs in the mitochondria of hepatocytes
- ATP is an allosteric inhibitor, while GDP and ADP are allosteric activators
Non-Oxidative Deamination
- Serine and Threonine can be deaminated directly by specific deaminases
- Examples: Serine → Pyruvate + NH4+, Threonine → α-ketobutyrate + NH4+
Hydrolytic Deamination
- Hydrolysis of the amide groups of glutamine and asparagine
- Examples: Glutamine → Glutamate + NH4+, Asparagine → Aspartate + NH4+
Direct Deamination
- Histidine → Urocanate + NH3
Urea Synthesis
- The liver is the major site of nitrogen metabolism in the body
- Urea synthesis involves the removal of the amino group from amino acids
- The carbon skeletons produced from amino acids are degraded to form various metabolic products
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