Questions and Answers
What is the ring structure attached to ribitol in the riboflavin molecule?
What is the energy source required for the conversion of riboflavin to its active co-enzyme forms?
What is the product formed when FMN is reoxidized by molecular oxygen?
What is the name of the enzyme that contains FMN in the respiratory chain?
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How many ATP molecules are generated when FADH2 is oxidized in the electron transport chain?
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What is the cause of riboflavin deficiency in humans?
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What is the earliest sign of riboflavin deficiency?
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What is the color of the tongue in riboflavin deficiency?
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What is the daily requirement of riboflavin for adults on sedentary work?
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Which of the following is not a rich source of riboflavin?
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What is the additional requirement of riboflavin during pregnancy, lactation and old age?
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Which enzyme is involved in the conversion of succinate to fumarate?
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What is the role of riboflavin in the body?
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Study Notes
Structure of Riboflavin
- Riboflavin has a dimethyl isoalloxazine ring attached to a ribitol, which is the alcohol of ribose sugar.
- Riboflavin is heat stable.
Co-enzyme Activity of Riboflavin
- Riboflavin exists in tissues tightly bound to enzymes, forming flavoproteins.
- The two coenzymes of riboflavin are FMN (flavin mono nucleotide) and FAD (flavin adenine dinucleotide).
- FAD accepts two hydrogen atoms from substrate during oxidation, reducing it to FADH2.
- The two nitrogen atoms of the isoalloxazine nucleus accept the hydrogen atoms.
FAD-dependent Enzymes
- FAD-dependent enzymes are involved in various reactions, including succinate to fumarate, acyl CoA to alpha-beta unsaturated acyl CoA, xanthine to uric acid, pyruvate to acetyl CoA, and alpha ketoglutarate to succinyl CoA.
FMN-dependent Enzymes
- FMN-dependent enzymes are involved in amino acid oxidation, where FMN is reduced and then reoxidized by molecular oxygen to produce hydrogen peroxide.
- In the respiratory chain, NADH dehydrogenase contains FMN, transporting electrons in the following manner: NAD+ → FMN → CoQ.
Riboflavin Deficiency
- Riboflavin deficiency is uncommon in humans due to synthesis by intestinal flora.
- Deficiency usually accompanies other deficiency diseases, such as beriberi, pellagra, and kwashiorkor.
- Symptoms of riboflavin deficiency are confined to skin and mucous membranes, including glossitis, magenta-colored tongue, cheilosis, angular stomatitis, circumcorneal vascularization, and proliferation of bulbar conjunctival capillaries.
Dietary Sources and Daily Requirement
- Rich sources of riboflavin include liver, dried yeast, egg, and whole milk.
- Good sources include fish, whole cereals, legumes, and green leafy vegetables.
- The daily requirement of riboflavin is related to calorie intake, with adults on sedentary work requiring about 1.5 mg per day.
- Additional 0.2 to 0.4 mg/day are required during pregnancy, lactation, and old age.
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Description
Learn about the structure of riboflavin, its co-enzyme forms FMN and FAD, and its role in flavoproteins. Understand how riboflavin is converted to its active forms with the help of ATP.
