BETHY NGUYEN
CHEMISTRY 12B
SPRING, 2006
INTRODUCTION
Green tea is natural dried leaves of the tea
plant, camellia sinensis.
 Most of the polyphenols in green tea are
flavanols, commonly known as catechins.
 The primary catechins in green tea are
epicatechin, epicatechin-3-gallate (ECG),
epigallocatechin (EGC), and
epigallocatechin-3-gallate (EGCG).
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INTRODUCTION (CONT.)
http://www.micronutrient.org/IDPAS/pdf/447GreenTea.pdf#search='mechanism%20of%20phenol%20in%20green%20tea'
What are Antioxidants?
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Green tea is regarded as an antioxidant. The polyphenols, especially EGCG.
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The human body constantly produces unstable molecules called oxidants,
also commonly referred to as free radicals.
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These free radicals readily react and damage other molecules and cell
DNA. Antioxidants "mop up" these free radicals and eliminate them before
they can damage healthy tissue.
Furthermore, oxidative damage by free radicals on low density lipoproteins
(LDL) is believed to be a precursor in the development of atherosclerosis
and coronary heart disease.
Oxidation to cell membranes and other cell components is also theorized to
be part of the aging process.
http://www.imperialteagarden.com/greenteaantioxidants.html
MECHANISM OF ANTIOXIDANTS
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Antioxidants are molecules that can
neutralize free radicals by accepting or
donating an electron to eliminate the
unpaired condition
Example of Formation of a complex
between the lipid radical and the
antioxidant radical (free radical acceptor).
http://class.fst.ohio-state.edu/fst821/Lect/AA.pdf
Mechanisms of Metals in
Accelerating Lipid Oxidation
http://class.fst.ohio-state.edu/fst821/Lect/AA.pdf
MECHANISMS OF FATTY ACID OXIDATION
Autoxidation by free radical reaction, In a peroxidefree lipid system.
1.Initiation:
the initiation of a peroxidation sequence refers to the
attack of a ROS able to abstract a hydrogen atom
from a methylene group (- CH2-). This attack
generates easily free radicals from polyunsaturated
fatty acids. OH is the most efficient ROS to do that
attack, whereas O2.- is insufficiently reactive.
The carbon radical tends to be stabilized by a molecular rearrangement
to form a conjugated diene.
Under aerobic conditions conjugated dienes are able to
combine with O2 to give a peroxyl (or peroxy) radical, ROO..
2. Propagation
As a peroxyl radical is able to abstract H from another
lipid molecule (adjacent fatty acid), especially in the
presence of metals such as copper or iron, thus causing
an autocatalytic chain reaction. The peroxyl radical
combines with H to give a lipid hydroperoxide (or
peroxide).
http://www.cyberlipid.org/perox/oxid0006.htm#3
TERMINATION
Termination (formation of a hydroperoxide) is most often achieved by
reaction of a peroxyl radical with a-tocopherol which is the main lipophilic
"chain-breaking molecule" in the cell membranes.
OXIDATIVE DAMAGE TO DNA:
formation of 8−OHdG/8−oxoG
8−OHdG from Guanosine with Hydroxyl
8−oxoG
8−OHdG/8−oxoG is the most commonly studied biomarker of DNA
oxidation [1] and is believed to constitute 5% of all oxidative DNA damage
[2] 8−OHdG is mutagenic because it inhibits methylation
and because it can be paired with adenosine rather than cytosine during DNA
replication leading to GC-to-AT conversion
http://www.benbest.com/lifeext/aging.html#mitochondria
BENEFIT OF GREEN TEA
POLYPHENOLS
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Years of research, in the United States and
Japan support the theory that Tea (Camellia
Sinensis) has the ability to ward off many types
of cancer
The belief is that polyphenol (-)-epigallocatechin
gallate (EGCG) have an inhibitory effect on the
enzyme, urokinase, which is required for tumor
formation.
help prevent the oxidation of LDL cholesterol.
The phenol groups in Green Tea polyphenols are
extremely active, easily able to capture and
neutralize free radicals and other pro-oxidants
Conclusion
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In conclusion, green tea and its polyphenols
(catechins)-- gallocatechin, epigallocatechin,
epicatechin, epigallocatechin, and epicatechin
gallate-- have been shown to not only inhibit
carcinogenesis before it begins, and decrease
the number of tumors, but also, amazingly,
induce apoptosis and cell cycle arrest in
carcinoma cells, as well.
Nevertheless, more work is required to elucidate
the molecular and clinical chemopreventive
effects of green tea on human colorectal cancer.
http://carbon.hampshire.edu/~cjarvis/NS120/projects/gt&cancer.htm
REFERRENCES
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http://www.pdrhealth.com/drug_info/nmdrugprofiles/nutsupdrugs/gre_0319.shtml
http://www.micronutrient.org/IDPAS/pdf/447GreenTea.pdf#search='mechanism%20
of%20catechins%20in%20green%20tea‘
http://www.cyberlipid.org/perox/oxid0006.htm#3
http://class.fst.ohio-state.edu/fst821/Lect/AA.pdf
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/R/ROS.html
JOURNALS:
1.MUTATION RESEARCH 424:51-58 (1999)
2. MUTATION RESEARCH; Dizdaroglu;M; 275(2-6):331-342 (1992)