18 Questions
How are nonessential amino acids synthesized from essential amino acids?
By amidation of essential amino acids
What is the reactant in the synthesis of glutamine?
Glutamate
Which amino acid can be formed from glycine?
Serine
What is the result of the transamination reaction involving α-keto acids?
Synthesis of alanine, aspartate, and glutamate
Which amino acid is synthesized from glutamate by cyclization and reduction reactions?
Proline
What is the common characteristic of glutamine and asparagine?
Both contain an amide group
What is the main symptom of Albinism?
Deficiency of melanin
What is the name of the disease that is characterized by the presence of phenylketone in the urine?
Phenylketonuria (PKU)
What is the treatment for Maple syrup urine disease?
Low-protein or modified diet with supplementation of thiamine pyrophosphate and limiting the intake of valine, leucine, and isoleucine
What is the mode of inheritance of Albinism?
Different modes
What is the cause of Pellagra?
Too little niacin or tryptophan in the diet or a failure to absorb these nutrients
What is the characteristic of the urine in Maple syrup urine disease?
Distinct maple syrup odor
What is the point of entry into metabolism for several non-polar amino acids?
Succinyl Coenzyme A
What is required for the synthesis of cysteine to be sustained?
Enough dietary intake of methionine
What is the consequence of a mutant gene in amino acid metabolism?
Total loss of enzyme activity
What is the result of the absence of homogentisate oxidase in the body?
Alcaptonuria
What is the precursor of tyrosine synthesis?
Phenylalanine
What is the fate of the carbon skeletons of amino acids after removal of the amino group?
They are converted into glucose, fatty acids, ketone bodies, or oxidized by the citric acid cycle
Study Notes
Amino Acid Metabolism Disorders
- Homogentisic acid accumulates and is excreted in the urine, turning black upon exposure to air, with symptoms including:
- Darkened urine in diapers (children)
- Darkening of the ear and formation of dark spots on the sclera and cornea (adults)
- Arthritis
Phenylketonuria (PKU)
- Caused by a deficiency of phenylalanine hydroxylase
- Characterized by the accumulation of phenylalanine and a deficiency of tyrosine
- Symptoms include:
- Presence of phenylketone (phenylpyruvate) in the urine
- CNS symptoms, such as mental retardation
- Hypopigmentation
- Treatable by dietary means
Maple Syrup Urine Disease
- Rare autosomal recessive disorder
- Caused by a partial or complete deficiency in branched-chain α-keto acid dehydrogenase
- Symptoms include:
- Feeding and vomiting problems
- Distinct maple syrup odor of urine
- Elevated levels of acids (especially leucine) in the blood, leading to physical and mental retardation in newborns
- Treatment involves a low-protein or modified diet, supplementation with high doses of thiamine pyrophosphate, and limiting the intake of valine, leucine, and isoleucine
Albinism
- Caused by a defect in tyrosine metabolism
- Results in a deficiency of melanin
- Inherited in different modes
Pellagra
- Caused by a lack of niacin or tryptophan in the diet, or failure to absorb these nutrients
- Can also occur due to a biosynthetic defect
Non-Essential Amino Acids
- Synthesized from intermediates of metabolism
- Some non-essential amino acids (tyrosine, cysteine) are made from essential amino acids (phenylalanine and methionine)
Synthesis of Non-Essential Amino Acids
- Alanine, aspartate, and glutamate are synthesized by transamination reactions
- Glutamine and asparagine are synthesized by amidation of glutamate and aspartate, respectively
- Other synthesis reactions involve proline, serine, glycine, and cysteine
Synthesis of Specific Amino Acids
- Cysteine is derived from methionine (essential amino acid)
- Tyrosine is synthesized by hydroxylation of phenylalanine
Metabolic Defects in Amino Acid Metabolism
- Inborn errors of metabolism are caused by mutant genes
- Result in abnormal proteins, often enzymes, leading to total loss or partial deficiency in catalytic activity
- Without treatment, can lead to mental retardation due to harmful accumulation of metabolites
Alcaptonuria
- Inherited disorder of tyrosine metabolism
- Caused by the absence of homogentisate oxidase
Learn about the synthesis of nonessential amino acids from intermediates of metabolism, including transamination and amidation reactions.
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