38 Questions
Histamine is a vasoconstrictor.
False
Dopamine is an intermediate in the formation of adrenaline.
True
GABA is a vasoconstrictor and a neurohumoral agent in the venoms of wasps.
False
Transamination involves the transfer of a keto group from a keto-acid to an amino acid.
False
Glutamate dehydrogenase is a simple enzyme that catalyzes the oxidative deamination of L-glutamate.
False
D-Amino acid oxidase is present in the liver, kidney, and brain.
True
Serine and Threonine are deaminated by specific deaminases in a reaction preceded by hydration.
False
The liver is not a major site of nitrogen metabolism in the body.
False
The carbon skeletons produced from amino acids are degraded to form 5 metabolic products.
False
Amino acid catabolism begins by adding the amino group.
False
Lysine is a guianidinium ion that is always protonated.
False
Threonine has one chiral carbon.
False
Asparagine is an amide of glutamic acid.
False
Leucine is a glycogenic amino acid.
False
Isoleucine is only a ketogenic amino acid.
False
Amino acid molecules in the amino acid pool come only from dietary proteins.
False
Porphyrin is synthesized from fatty acids.
False
A positive nitrogen balance occurs when nitrogen intake equals nitrogen loss.
False
The reaction of deamination involves the removal of the β-amino group from amino acids.
False
Oxidative deamination is a reversible biochemical reaction.
True
Transamination reactions are catalyzed by Oxidase enzymes.
False
Lysine is an amino acid that participates in transamination reactions.
False
Pyridoxal phosphate (PLP) serves as the cofactor for oxidative deamination reactions.
False
Vitamin B6 is derived from pyridoxal phosphate (PLP).
False
Ornithine transcarbamoylase is the enzyme responsible for the conversion of citrulline to arginosuccinate.
False
The urea cycle occurs exclusively in the cytoplasm.
False
Argininosuccinate synthetase is the enzyme responsible for the conversion of citrulline to arginine.
False
The urea cycle is activated by N-acetylglutamate.
True
Pyrophosphatase is involved in the reaction catalyzed by argininosuccinate synthetase.
True
The enzyme arginase is responsible for the conversion of arginine to ornithine and urea.
True
The urea cycle requires four ATP molecules.
False
Ornithine is regenerated at the end of the urea cycle.
True
Urea is produced in the kidneys of ureotelic animals.
False
Arginase is found in significant amounts in the kidney.
False
The net reaction for the urea cycle involves the production of urea and fumarate.
True
Fumarate is a component of the urea cycle.
False
Oxaloacetate can be used in energy generation or converted to glucose or aspartate.
True
Urea is eliminated in the urine by the liver.
False
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
This quiz covers the properties and classification of amino acids, including lysine, arginine, serine, threonine, and asparagine, including their protonation states and hydrogen bonding capabilities.
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