introduction to b-vitamins: role of b-vitamins in metabolic pathways sept 10, 2014
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INTRODUCTION TO B-VITAMINS: ROLE OF B-VITAMINS IN METABOLIC PATHWAYS Sept 10, 2014. We get energy on a daily basis from carbohydrates, lipids, and proteins. What events must occur, to enable us to employ these dietary components for energy?. NIACIN is vitamin needed for a great many - PowerPoint PPT PresentationTRANSCRIPT
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INTRODUCTION TO B-VITAMINS:
ROLE OF B-VITAMINS IN METABOLIC PATHWAYS
Sept 10, 2014
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We get energy on a daily basis fromcarbohydrates, lipids, and proteins.
What events must occur, to enableus to employ these dietary componentsfor energy?
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NIACIN is vitamin needed for a great manyevents in energy metabolism.
Two forms of niacin in the diet are shown: these areprecursors for NADH and NADPH
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NIACIN AS A COMPONENTOF NADH AND NADPH:
These participate in >200biochemical reactions that
are essential for health!
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EACH RED ARROWIS A STEP IN FORMATIONOF ATP FROM GLUCOSE,THAT USES NIACIN
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FADH2 is a riboflavin-dependentcomponent. The FADH2 produced
also contributes electronsfor ATP synthesis by the ETC
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GLYCOLYSIS: The molecular steps are easily seen.
ROLE FOR NIACIN
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USEFUL EXERCISE:Draw out the intermediatesin the TCA cycle
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O
H2C
H2C
C
CO
O
CO
O
O
H2C
H2C
C
CO
O
SCoA
alpha-ketoglutarate succinyl-CoA
NAD+
Acetyl-CoA
NADH
CO2
REACTION CATALYZED BY THE ENZYMEa-KETOGLUTARATE DEHYDROGENASE(PANTOTHENIC ACID is involved, will be discussed)
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NADH (which contains niacin) carries most of the electrons from the TCA to the electron-transport chain.
The NAD+ is regenerated, to be used again MANY times.
FromTCA
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This is VERY simplified, of course. It really justshows the REACTANTS and the PRODUCTS.
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The niacin functional group as a redoxdonor/acceptor of electrons
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CH3 - C - COO-
H
OH?
Lactate
NAD+
Reaction catalyzed by LDH
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CH3 - C - COO-
O?
Pyruvate
NADH
Another reaction catalyzed by LDH
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Glutamate is the main amino acid that donates nitrogento the urea cycle. NADH is required for this reaction.
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Niacin (as NAD)is required for themetabolism ofethanol.
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The metabolic fateof lysine – HOW MANYniacin-dependent steps?
Amino acids are degradedfor energy in normalmetabolism, we will discussin some detail.
Notice the Acetyl-CoA product,which can be used by the TCAcycle to make ATP.
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OTHER B-VITAMINS HAVE ESSENTIAL ROLES IN ENERGY METABOLISM
Pantothenic acid: allsteps that use CoA
Thiamine
Riboflavin
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Thiamine: as provided in the diet
The active form of thiamine in metabolism
SEPARATEENZYMES EXISTTO ACTIVATEEACH B-VITAMIN:
Thiamine is modifiedby addition oftwo PO4 groups
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SEVERAL ENZYMES WORK TOGETHER IN THEPYRUVATE DEHYDROGENASE COMPLEX:
WHAT IS THE FATE OF THE 3 CARBONS INTHE INITIAL PYRUVATE MOLECULE?
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Wet Beriberi: edema Wet Beriberi: edema is a common feature.is a common feature.
What is the What is the diagnostic challenge?diagnostic challenge?
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Pellagra: dermatitis is typicalPellagra: dermatitis is typical
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Pellagra/before and after treatment with high-dose niacin: which biochemical
steps are disturbed, that involve niacin?
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This graphic shows that somedietary tryptophan is convertedto NIACIN.
The yield is is about 1 mg ofniacin, for 60 mg of tryptophan.
Corn is a problem becauseits niacin content is often not bioavailable, and because corn is low in tryptophan.
The niacin RDA (20 mg) is basedon a lot of our niacin (another20 mg) coming from tryptophan.
People who cannot make niacinare given about 50 mg/day.
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MICRONUTRIENT DEFICIENCY: Often very non-specific.
How can we be prepared to diagnose these disorders?
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USEFUL STUDY ASSIGNMENT:
-Suppose you ate a VERY limited diet, withfoods that are NOT fortified. What nutrientswould be deficient?
-corn
-potatoes
-white rice
-wheat
This can happen during a famine, where there is a sharpreduction in the diversity of the diet.