PDH and the TCA Cycle

Question 1

What is the role of coenzymes in fuel metabolism?

Answer 1

They are electron carriers.

• NAD+/NADH & NADP+/NADPH = 2 e donor/acceptors.
  - Diffusible and NOT permanently attached to enzymes.
  - Biologically active forms of niacin/nicotinic acid (vitamin B3).
• FAD/FADH2 = 2 e donor/acceptor
  - Prosthetic group: permanently attached to enzymes.
  - Biologically active forms of riboflavin (vitamin B2)

Question 2

What is the function of niacin? What disease is associated with niacin deficiency?

Answer 2

• Synthesized from tryptophan.
• Dietary sources: unrefined and enriched grains and cereal, milk, lean meats, and liver.
• Deficiency = pellagra (skin, GI and CNS symptoms, 3 D’s)
• Dermatitis (photosensitive), Diarrhea and Dementia
• Sometimes seen in chronic alcoholics and tryptophan metabolism disorders.

Question 3

What is the function of riboflavin? What disease is associated with riboflavin deficiency?

Answer 3

• Dietary sources = milk, eggs and liver.
• Deficiency = ariboflavinosis
• Symptoms: Dermatitis, cheilosis and glossitis (magenta tongue).
• Sometimes seen in chronic alcoholics.

Question 4

What is the function of thiamine? What disease is associated with thiamine deficiency?

Answer 4

•Thiamine also required for transketolase (HMP) and a-ketoglutarate dehydrogenase (TCA cycle)
oThiamine deficiency: (vitamin B1)
•Dietary sources: whole grain cereals, liver, pork, yeast and legumes.
•Usually occurs in areas where rice is major component of diet.
•Results in:
•Beriberi:
oWet: edema and CV symptoms.
oDry: muscle wasting and peripheral neurologic dysfunction.
•Also seen in chronic alcoholics because EtOH interferes w/ thiamine absorption leading to:
•Wernicke encephalopathy: reversible (ataxia, confusion, nystagmus)
•Korsakoff syndrome: irreversible (deficits in learning & memory)
•Wernicke-Korsakoff syndrome: two syndromes observed together.

Question 5

What is the function of CoA and Pantothenic Acid? What disease is associated with CoA and Pantothenic Acid deficiency?

Answer 5

oCoA & Pantothenic Acid
•Synthesized from pantothenate/panthothenic acid.
•Dietary sources: most foods but eggs and yeast are good sources.
•Deficiency:
•Causes burning foot syndrome (observed in POWs of WWII).
oSymptoms: painful burning feet, irritability, restlessness, fatigue, apathy, sleep disturbances, GI distress, nausea, vomiting and abdominal cramps.