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Lecture 13

NUTR 3210 Lecture Notes - Lecture 13: Citric Acid Cycle, Dehydrogenation, Riboflavin

Course Code
NUTR 3210
David Mutch

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Micronutrients Part 2
Involved in Oxidant Defense
- Vitamin E
- Selenium
- Vitamin C
- Sulfur amino acids
- Niacin
- Riboflavin
- Copper/Zinc/Manganese
Reduction-Oxidation Reactions
- Redox
o Transfer of electrons between two substrates
o Biochemical reactions are essentially electron transfer reactions (REDOX)
Kreb’s cycle
Pyruvate dehydrogenation
Lactic acid production
- Large number of
micronutrients have redox
- Principle electron carriers
are NADH and FADH2
- These are important for the
creation of ATP
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Reactive Oxygen Species (ROS)
- Reactive oxygen species are produced as a by-product of the ETC when electron flow
fails (about 1% leakage)
o So, ETC is only 99% effective
- This occurs in an oxygen-rich environment, so oxygen can, as a result, react with
- H2O2 can be converted to water by catalase, glutathione peroxidase
o This enzyme is selenium dependent
- As the diagram
shows, when oxygen reacts
with 1 electron it forms
superoxide anion radicals =
modest reactivity
- Then, by SOD
(superoxide dismutase),
superoxide anion radical can
become hydrogen peroxide
(modest reactivity)
o SOD uses copper and
zinc as electron donor
o A mutation in SOD =
Lou Gehrig’s ASL
- Then hydrogen
peroxide can react with an
electron to form hydroxyl
radical (incredibly reactive)
o This can then attack
macromolecules (DNA,
o Leads to cancer and
cell death
So, superoxide anion radical becomes hydrogen
peroxide by SOD and then hydrogen peroxide can
become water OR it will become converted to
hydroxyl radical, which can mutate DNA, cause
lipid peroxidation, or mitochondrial permeability
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o Important for the pathogenesis of many
diseases BUT it can also be destructive to
the cell and result in cell death
Need to understand that ROS are important for normal functions, they are not just destructive.
Ex: for T3 and T4 production
Vitamin E
- Encompasses 8 compounds (vitamers)
o 4 tocopherols
Have saturated side chains with 16 carbons
o 4 tocotrienols
Have unsaturated side chains with 16 carbons
- Each of these 2 classes is composed of 4 vitamers that differ in the number and location
of methyl groups on the chromanol ring (different degrees of methylation)
o Vitamers in both classes are designated as alpha, beta, gamma, or theta
So, alpha tocopherol, beta tocopherol, gamma tocopherol, theta tocopherol
And, alpha tocotrienol, beta tocotrienol, gamma tocotrienol
- Only alpha-tocopherol has biological activity in the body and can meet the body’s need
(requirement) for the vitamin antioxidant defense
o So, the body cannot interconvert the vitamers
- All vitamers are found naturally in foods
- Tocopherol is derived from the Greek word tokos, which means childbirth and phero,
which means to bear or bring forth
o Based on work showing that rats could not reproduce when vitamin E was absent
from the diet
Vitamin E 4 Tocopherols
- ALL have saturated side chain
- Contain a phenolic functional group on a
chromanol ring (sometimes called the head of the
molecule) and an attached phytyl side chain
(phytyl tail), which includes the saturated fatty
- Alpha is the most methylated ring
- Nomenclature is used to describe the number and
position of the ring CH3 groups
- All 4 have the hydroxyl group, which is the
antioxidant site
- They are found free in foods
o Found in dietary plant oils
o Absorbed passively
- R and S configuration is determined by the first 3
methyl groups on side chain (RRR)
o Page 401
- Natural alpha-tocopherol is in the RRR configuration
o Fits in tocopherol transfer protein (TTP)
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