Amino Acid: Metabolic Disorder MCQs

Answer- A. Tyrosine Phenylketonuria: Autosomal recessive Deficiency of phenylalanine hydroxylase. Defect in conversion of phenylalanine to tyrosine. This leads to increase level of phenylalanine. This increase phenlylalanine converted into phenylpyruvate and phenyl acetate. This phenyl acetate gives mousy or musty odour in urine/body.

Ans. is 'a' i.e.Isolvaleryl CoA dehydrogenase - Isovaleric acidemia is due to the defect in the metabolism of leucine. -The enzyme defective is isovaleryl Co-A dehydrogenase. -A characteristic odor of sweaty feet is present. -Vomiting, acidosis, and coma follow the ingestion of excess protein. Accumulated isovaleryl-CoA is hydrolyzed to isovalerate and excreted. 341. Which of the following metabolites is involved in glycogenolysis, glycolysis and gluconeogenesis ? a) Galactose-l-phosphate b) Glucose-6-phosphate c) Uridine diphosphoglucose d) Fructose-6-phosphate Correct Answer - B Ans. is 'b' i.e., Glucose-6-phosphate [Ref Harper 28th le p. 166, 158] → Glucose-6-phosphate is the metabolite which :?

Glucose Is Always Required by the Central Nervous System and Erythrocytes Erythrocytes lack mitochondria and hence are wholly reliant on (anaerobic) glycolysis and the pentose phosphate pathway at all times. The brain can metabolize ketone bodies to meet about 20% of its energy requirements; the remainder must be supplied by glucose. The metabolic changes that occur in the fasting state and starvation serve to preserve glucose and the body’s limited glycogen reserves for use by the brain and red blood cells, and to provide alternative metabolic fuels for other tissues. So Option A is the correct option.

Garrod’s Tetrad includes - Alkaptonuria Albinism Pentosuria Cystinuria Garrod introduced the term "inborn errors of metabolism" in 1908. Reference: Harper's 32nd edition, page 305 Vasudevan and Sreekumari 8/e p293

Clinical Manifestations of phenylketonuria (PKU) - The affected infant is normal at Profound mental retardation develops gradually if the infant remains untreated. Cognitive delay may not be evident for the 1st few months. Some may have a seborrheic or eczematoid rash , which is usually mild and disappears as the child grows older. These children have an unpleasant odor of phenylacetic acid , which has been described as musty or mousey . Reference: Vasudevan and Sreekumari 8/e p292 Reference: Harper's 32nd edition, chapter - 27

Phenylketonuria is due to deficiency of phenylalanine hydroxylase . Dietary restriction of phenylalanine with supplementation of tyrosine is needed as tyrosine is a non-essential amino acid synthesized from phenylalanine by the action of phenylalanine hydroxylase. Reference: Harper's 32nd edition, page 304

Maple Syrup Urine Disease Biochemical defect Deficiency of the enzyme Branched Chain Ketoacid Dehydrogenase. Defective reaction is Defective Decarboxylation. Clinical features Mental Retardation Convulsion Acidosis, Coma Smell of Burnt Sugar [Maple Syrup] Tests for MSUD Di Nitro Phenyl Hydrazine Test (DNPH Test) Rothera's Test Enzyme Analysis Treatment Restrict Branched Chain Amino Acid Give high doses of Thiamine. Reference: Harper's 32 nd edition, page 276-278

The primary goal of therapy is to reduce phenylalanine levels in the plasma and brain. Phenylketonuria - Hyperphenylalaninemia arise from defects in - Phenylalanine hydroxylase , (type I, classic phenylketonuria (PKU), frequency 1 in 10,000 births) Dihydrobiopterin reductase (type II and III) Dihydrobiopterin biosynthesis (type IV and V) Alternative catabolites are excreted. A diet low in phenylalanine can prevent the mental retardation of PKU. DNA probes facilitate prenatal diagnosis of defects in phenylalanine hydroxylase or dihydrobiopterin reductase. Treatment of Classical PKU A low-phenylalanine diet. Administration of large neutral amino acids is another approach to diet therapy. Reference: Harper's Illustrated Biochemistry, 32 nd Edition, Page Number-304.