Synthesis of Nonessential Amino Acids

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Questions and Answers

How are nonessential amino acids synthesized from essential amino acids?

Through a series of enzyme-catalyzed reactions

By transamination reaction

By cyclization and reduction reactions

By amidation of essential amino acids (correct)

What is the reactant in the synthesis of glutamine?

Alanine

Aspartate

Glutamate (correct)

Glycine

Which amino acid can be formed from glycine?

Tyrosine

Asparagine

Serine (correct)

Alanine

What is the result of the transamination reaction involving α-keto acids?

Synthesis of alanine, aspartate, and glutamate Signup and view all the answers

Which amino acid is synthesized from glutamate by cyclization and reduction reactions?

Proline Signup and view all the answers

What is the common characteristic of glutamine and asparagine?

Both contain an amide group Signup and view all the answers

What is the main symptom of Albinism?

Deficiency of melanin Signup and view all the answers

What is the name of the disease that is characterized by the presence of phenylketone in the urine?

Phenylketonuria (PKU) Signup and view all the answers

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 Signup and view all the answers

What is the mode of inheritance of Albinism?

Different modes Signup and view all the answers

What is the cause of Pellagra?

Too little niacin or tryptophan in the diet or a failure to absorb these nutrients Signup and view all the answers

What is the characteristic of the urine in Maple syrup urine disease?

Distinct maple syrup odor Signup and view all the answers

What is the point of entry into metabolism for several non-polar amino acids?

Succinyl Coenzyme A Signup and view all the answers

What is required for the synthesis of cysteine to be sustained?

Enough dietary intake of methionine Signup and view all the answers

What is the consequence of a mutant gene in amino acid metabolism?

Total loss of enzyme activity Signup and view all the answers

What is the result of the absence of homogentisate oxidase in the body?

Alcaptonuria Signup and view all the answers

What is the precursor of tyrosine synthesis?

Phenylalanine Signup and view all the answers

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 Signup and view all the answers

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