Co-enzyme Forms of Niacin and NAD+ Reduction

Questions and Answers

What is the primary function of NADPH in cellular reactions?

Energy production in mitochondria

Protein synthesis

Reductive biosynthetic reactions (correct)

Oxidative biosynthetic reactions

What is the outcome of niacin deficiency?

Beriberi

Scurvy

Rickets

Pellagra (correct)

What is the underlying cause of dermatitis in pellagra?

Tryptophan deficiency

Sunlight exposure (correct)

Estrogen metabolites

Niacin deficiency alone

Which enzyme is involved in the synthesis of NAD+ from tryptophan?

Quinolinate phosphoribosyl transferase Signup and view all the answers

What is the characteristic skin lesion seen in pellagra?

Casal's necklace Signup and view all the answers

Which of the following is NOT a symptom of pellagra?

Hemophilia Signup and view all the answers

What is the role of NAD+ in the cell?

Source of ADP-ribose for protein modification Signup and view all the answers

What is the name of the pathway that generates NADPH?

Hexose monophosphate shunt pathway Signup and view all the answers

What is the resulting compound when niacin is attached to a ribose phosphate?

Mononucleotide Signup and view all the answers

What is the difference between NAD+ and NADP+?

One more phosphoric acid is attached to the ribose of AMP in NADP+ Signup and view all the answers

What happens to the nitrogen atom of niacinamide in the oxidized form of the co-enzyme?

It contains one positive charge Signup and view all the answers

What is the net result of NAD+ accepting one H atom and one e?

Formation of NADH and release of H+ Signup and view all the answers

Which of the following enzymes is NOT a NAD+ dependent enzyme?

Hexokinase Signup and view all the answers

What is the result of the oxidation of NADH in the respiratory chain?

Generation of 2½ ATP Signup and view all the answers

What is the function of NAD+ in the process of reduction?

It accepts one hydrogen atom and one electron Signup and view all the answers

What is the difference between the oxidized and reduced forms of the co-enzyme?

The oxidized form has a positive charge while the reduced form has no charge Signup and view all the answers

Study Notes

Co-enzyme Forms of Niacin

Niacin is converted to its co-enzyme forms, Nicotinamide adenine dinucleotide (NAD+) and Nicotinamide adenine dinucleotide phosphate (NADP+).
Niacin is attached to a ribose phosphate to form a mononucleotide, then attached to AMP to form the dinucleotide.
The nitrogen atom of niacinamide contains one positive charge, hence the structure is abbreviated as NAD+.
NADP+ has one more phosphoric acid attached to the ribose of the AMP.

Reduction of NAD+

In the oxidized form, the nitrogen of the nicotinamide residue has a positive charge.
In the process of reduction, NAD+ accepts one hydrogen atom fully and one electron, and the positive sign in the molecule is removed.
NAD+ dependent enzymes include lactate dehydrogenase, glyceraldehyde-3-phosphate dehydrogenase, and more.

NADH and NADPH

One NADH molecule is oxidized in the respiratory chain to generate 2½ ATPs.
NADPH is used almost exclusively for reductive biosynthetic reactions.
NADPH generating reactions include glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase.
NADPH utilizing enzymes include glutathione reductase and more.

Niacin Deficiency

Deficiency of niacin leads to the clinical condition called pellagra.
Pellagra is caused by the deficiency of Tryptophan as well as Niacin.
Symptoms of pellagra include dermatitis, diarrhea, and dementia.

Pellagra Symptoms

Dermatitis: bright red erythema occurs, especially in the feet, ankles, and face.
Diarrhea: may be mild or severe with blood and mucus, leading to weight loss.
Dementia: frequently seen in chronic cases, with delerium, irritability, and more.