Definition - Organic compound required in small amounts.
Vitamin B1, B2, B3, B5, B6, B7, B9, B12
A few wordsabout each.
Sourcesin diet - Many plants(photoreceptors), also meat, especially liver. Fat
soluble, so you can get too much, or too littleif absorption isaproblem.
Vitamin A - Retinol
Retinol (vitamin A)
Vision (11-cis-retinol bound to rhodopsin detectslight in our eyes).
Regulating genetranscription (retinoic acid receptorson cell nuclei arepart of a
system for regulating transcription of mRNAsfor anumber of genes).
Vitamin B1 - Thiamine
Cofactor for several enzymes (aprecursor for thiaminepyrophosphate, oneof the
cofactorsused by thepyruvatedecarboxylasecomplex (PDC).
Also, acofactor for branched chain a-keto dehydrogenase.
Found in awidevariety of foods, including meat, grains. Deficiency causes
beriberi (muscleatrophy, neurological problems).
Vitamin B2 - riboflavin
FMN - Flavin
Riboflavin isaprecursor for
FAD and FMN.
FAD isacofactor for pyruvate
dehydrogenasecomplex (PDC), and
succinatedehydrogenasein TCA cycle.
FMN isan electron carrier in the
electron transport chain.
Vitamin B3 - nicotinic acid
(aprecursor for NAD).
Also known asniacin.
isneeded for glycolysis, NADH getsoxidized in electron transport chain,
Vitamin B5 - pantothenic acid (needed for making CoA)
Weget pantothenic acid in our diet asCoA, which must bebroken down to
pantothenic acid to beabsorbed in intestine. Wethen usethepantothenic acid
in making our own CoA.
Vitamin B6 - pyridoxine
Precursor for pyridoxal phosphate(PLP).
PLPisacovalently linked cofactor to
transaminases, and somedecarboxylases,
and glycogen phosphorylase; theseare
called “PLP-dependent enzymes”.
Vitamin B7 - Biotin.
Used in fatty acid synthesis, also
Biotin deficiency israre.
Wesaw biotin in chapter 14:
Vitamin B9 - Folic acid.
Required for synthesisof glycine,
methionine, nucleotidesT & U
Important for rapidly dividing cells(very
important in early pregnancy).
donor of methylenegroups.
Deficiency in pregnancy causesneural tubedefects.
Folic acid isnow added to many grain productsin theUS.
Wesaw cobalaminein fatty acid
Cobalamin isneeded in making
adenosylcobalamin, acofactor for
“methyl malonyl mutase”, which
breaksdown odd-chain fatty acids.
B12 isalso used in regenerating folate
Sourcesaremeat, milk and eggs.
Vegetarianswho eat dairy products
areOK, but non-dairy vegansmay not
Vitamin B12 - cobalamin.
(also hydroxycobalamin, adenosylcobalamin).
In almost all organisms, ascorbic acid issynthesized from glucosein 4 steps.
A relatively recent (40 million yearsago) mutation in theancestor of humans
madeusunableto makeascorbic acid. So for us, and someclosely related
Guineapigscan’t makeascorbic acid, either.
Sourcesof vitamin C arefruit and fresh meat. Vitamin C deficiency causes
scurvy, and in human history vitamin C deficiency may havebeen an
impediment to spreading northward.
Vitamin C - asorbic acid
Required for collagen synthesis, and asa
cofactor for several enzymes. Also
Vitamin D refersto agroup of similar lipid-solublemolecules(major forms
areD2 and D3, also D1, D4, D5).
Vitamin D3 (cholecalciferol) Vitamin D2 (ergocalciferol)
Vitamin D3 can beobtained in diet, or derived from cholesterol in areaction
that requiresUV light.
Vitamin D bindsto a“vitamin D binding protein” (VDP) for transport to target
Vitamin D isnot activeitself (it’saprohormone); it ismodified to yield
biologically activeforms, such ascalcitriol.
Calcitriol (derived from vitamin D) isatranscription factor, influencing expression
of proteinsinvolved in calcium absorption and transport.
Vitamin D isalso important for immunesystem function.
Deficiency causesrickets, boneloss.
Vitamin D production requiresUV light (sunlight).
Sometimeafter humansmigrated north out of Africaabout 50,000 yearsago,
mutationsappeared that reduced melanin (pigment) production in theskin,
permitting vitamin D production with lesssunlight.
Disadvantagesof lessmelanin production areskin that iseasily damaged by
thesun, skin cancer risk, and lossof folic acid dueto UV damage.
Themelanin-reducing mutationshelped early humansmakevitamin D in
northern europein winter.
mutationsresulting in the
most dramatic melanin
In Texas, thereistoo much sun and plenty of vitamin D, so I want
my melanin back !
It isessential, but rolesareunclear. Suggestions
Obtained in diet, deficiency israre.
Vitamin E - Collectively refersto 8 related tocopherols.
Vitamin K isrequired for proper blood clotting.
It isused in synthesizing gammacarboxy glutamate, apost-
translationally modified amino acid in prothrombin.
Sourcesarevegetablesand fruits, deficiency israre.
Vitamin K - Refersto phylloquinonone(vitamin K-1), and several
structurally similar molecules.