Micronutrients and Energy Metabolism Notes

Micronutrients in Energy Metabolism

• Micronutrients play a crucial role in energy metabolism, facilitating the processes of glycolysis, the Krebs cycle, and the electron transport chain.
• Electrons are carried in NADH and FADH2, which are essential for ATP production.

Learning Objectives

• Describe the functions, food sources, and deficiencies of key nutrients including niacin, riboflavin, thiamin, pantothenic acid, folate, and vitamin B12.
• Integrate the functions of micronutrients with key physiologic and metabolic processes.
• Note: Folate and vitamin B12 are also discussed in Unit 6 related to blood health.

Vitamins in Energy Metabolism

• B-Vitamins and Coenzyme Examples:
  • Thiamin
    • Coenzyme Example: Thiamin pyrophosphate (TPP) or Thiamin diphosphate (TDP)
    • Function/Transfer: Decarboxylation
  • Riboflavin
    • Coenzyme Example: Flavin adenine dinucleotide (FAD)
    • Function/Transfer: Electron (hydrogen) transfer
    • Coenzyme Example: Flavin mononucleotide (FMN)
    • Function/Transfer: Electron (hydrogen) transfer
  • Niacin
    • Coenzyme Example: Nicotinamide adenine dinucleotide (NAD)
    • Function/Transfer: Electron (hydrogen) transfer
    • Coenzyme Example: Nicotinamide adenine dinucleotide phosphate (NADP)
    • Function/Transfer: Electron (hydrogen) transfer
  • Pantothenic acid
    • Coenzyme Example: Coenzyme A (CoA)
    • Function/Transfer: Acyl (2-C groups) transfer
  • Biotin
    • Coenzyme Example: N-carboxylbiotinyl lysine
    • Function/Transfer: Carboxylation; $CO_2$ transfer
  • Vitamin B-6
    • Coenzyme Example: Pyridoxal phosphate (PLP)
    • Function/Transfer: Transamination: amino group transfer
  • Folic acid
    • Coenzyme Example: Tetrahydrofolic acid (THFA)
    • Function/Transfer: 1-carbon unit transfer
  • Vitamin B-12
    • Coenzyme Example: Methylcobalamin
    • Function/Transfer: 1-carbon unit transfer
  • Some B-vitamins form more than one coenzyme.

Check-in

• Outline at least two metabolic pathways where micronutrients support energy metabolism.
• A coenzyme is a non-protein chemical compound that is required for an enzyme's activity as a catalyst

Niacin

• Niacin exists in two forms: nicotinic acid (niacin) and nicotinamide (niacinamide).
• It functions as a COENZYME in energy metabolism.
  • NAD - nicotinamide adenine dinucleotide
  • NADP - phosphate form
• Tryptophan can be converted to niacin:
  • TRYPTOPHAN → NICOTINAMIDE (NIACIN)
  • This pathway depends on adequate intake of riboflavin and vitamin B6.

Metabolic Pathways and NAD/NADH

• NAD/NADH are involved in multiple metabolic pathways.
• Examples:
  • Glucose to Pyruvate.
  • Pyruvate to Acetyl-CoA.
  • Citric acid cycle.

Niacin - DRI

• DRI (Dietary Reference Intake) for niacin is based on mg of niacin or niacin equivalents (NE).
• $1 \, \text{mg niacin} = 60 \, \text{mg tryptophan}$
• NE depend on niacin and tryptophan eaten, as well as vitamin B6 and riboflavin adequacy.

Riboflavin

• Riboflavin functions as a COENZYME in energy metabolism.
  • FAD – flavin adenine dinucleotide
  • FMN – flavin mononucleotide
• Needed for production of other compounds in the body

Thiamin

• Thiamin functions as a COENZYME in energy metabolism, specifically as thiamin pyrophosphate (TPP).
• Plays a role in:
  • Pyruvate → Acetyl CoA + $CO_2$
  • TCA Cycle
• Component of nerve cell membranes.
• Absorption is inhibited, and excretion is enhanced by alcohol.

Pantothenic Acid

• A critical component of coenzyme A (CoA).
• Chemical structure of Coenzyme A:

$CH<em>3-\stackrel{\text{Acetyl}}{\text{C}}-S-CH</em>2CH<em>2-NH-\stackrel{\text{O}}{\text{C}}-CH</em>2CH<em>2-NH-\stackrel{\text{O}}{\text{C}}-\stackrel{\text{OH}}{\stackrel{\text{|}}{\text{CH}}}(\text{CH}</em>3)-\stackrel{\text{O}}{\text{C}}-\text{CH}<em>2\text{O}-\stackrel{\text{O}}{\stackrel{\text{|}}{\text{P}}}-\text{O}-\stackrel{\text{O}}{\stackrel{\text{|}}{\text{P}}}-\text{OCH}</em>2$

Metabolic Overview

• Acetyl-CoA acts as a convergence point for the metabolism of:
  • Glucose
  • Fatty acids
  • Amino acids
  • Alcohol

Check-in Table

• Vitamins and their coenzyme forms and examples of pathways:

Folate

• Folate = naturally occurring polyglutamate form.
• Folic acid = synthetic form (monoglutamate).
• Coenzyme – tetrahydrofolic acid (THFA).

Folate Functions

• Needed for DNA synthesis; works in tandem with vitamin B12.
• Involved in epigenetic modification of DNA.
  • Addition of methyl group ($CH_3$) to specific DNA section.

Vitamin B12

• Also known as cobalamin.
• Coenzyme form is methylcobalamin.
• Needed to form methionine from homocysteine.
• Needed to reform THFA (connection with folate).

Vitamin B12 Absorption

• GI tract issues can impact vitamin B12 absorption.

Study Guide Recommendations

• Create a chart of all micronutrients listed on the study guide, including categories such as functions, major food sources, deficiencies, and toxicities (see Table 12-2).
• Compare and contrast vitamins and minerals with regard to structure, function, absorption, and transport.