5.2 Vitamins

vitamin

an organic compound essential in small amounts that must be obtained from dietary sources

13

Number of known vitamins

water-soluble vitamins

class of vitamins carried in bloodstream, needed in frequent small doses, rapidly eliminated

fat-soluble vitamins

stored in fat tissues, needed in periodic doses, more likely to be toxic in excess

water-soluble vitamins

Water-soluble vs fat-soluble vitamins - travel without carriers

water-soluble vitamins

Water-soluble vs fat-soluble vitamins - kidneys remove excess in urine

water-soluble vitamins

Water-soluble vs fat-soluble vitamins - not likely to reach toxic levels when consumed from supplements

water-soluble vitamins

Water-soluble vs fat-soluble vitamins - function as coenzymes

fat-soluble vitamins

Water-soluble vs fat-soluble vitamins - many require protein carriers to travel

fat-soluble vitamins

Water-soluble vs fat-soluble vitamins - likely reach toxic levels when consumed from supplements

fat-soluble vitamins

Water-soluble vs fat-soluble vitamins - do not function as coenzymes

vitamin C

has the simplest structure of the 13 vitamins

vitamin C

vitamin that exists in two active forms in the human body – an oxidized form and a reduced form

vitamin C

the best known vitamin, functions as an antioxidant for water-soluble substances

vitamin C

was the first to be structurally characterized (1933) and the first to be synthesized in the laboratory (1933)

involves L-gulonic acid being converted into L-ascorbic acid

biosynthesis of vitamin C

lactonase

enzyme involved in converting L-gulonic acid into a cyclic ester. An oxidase then introduces a double bond into the ring producing L-ascorbic acid.

vitamin C

functions as an antioxidant, helps regenerate vitamin E, and a preservative

B vitamins

water-soluble vitamins that function as coenzyme precursors

8

How many known B vitamins are currently there?

B4, B8, B10, B11

long lost B vitamins (mga hindi kasama sa vitamins)

thiamin (vitamin B1)

coenzyme form is thiamin pyrophosphate (TPP)

thio - sulfur, amine - amine groups present

origin of the term “thiamin”

thiamin pyrophosphate (TPP)

coenzyme form of thiamin, a molecule in which a diphosphate group has been attached to the side chain.

riboflavin (vitamin B2)

“yellow vitamin” with coenzymes FAD and FMN

niacin (vitamin B3)

vitamin that forms NAD⁺ and NADP⁺ for redox reactions

Niacin

occurs in food in two different, but similar, forms (B vitamins)

Nicotinic acid

was first discovered in 1873, long before the concept of vitamins was known.. It was made by reacting nicotine with nitric acid

pantothenic acid (vitamin B5)

found in almost all plants and animals (B vitamins)

pantothen - from everywhere

Greek origin of the pantothenic acid (vitamin B5)

vitamin B6

a collective term of three related compounds which includes pyridoxine, pyridoxal, and pyridoxamine

vitamin B6

vitamin that helps in amino acid metabolism and supports the production of neurotransmitters

Pyridoxine

compound in vitamin B6 found mostly in plants

Pyridoxal and pyridoxamine

compounds in vitamin B6 found mostly in animal foods

biotin (vitamin B7)

Unique among the B vitamins that it can be obtained both from dietary intake and also via biotin- producing bacteria, microbiota, present in the human large intestine

biotin (vitamin B7)

acts as a coenzyme carrier for CO₂

folate (vitamin B9)

structure includes pteridine, PABA, and glutamate

folic acid

When only one glutamate residue is present, the folate is called __.

tetrahydrofolate (THF)

The active coenzyme form of folate, which has only one glutamate, and four hydrogen atoms have been added to the double-ring nitrogen system.

folium = leaf

Latin origin of folate

vitamin B12 (cobalamin)

contains cobalt and is the most complex vitamin

vitamin B12 (cobalamin)

the only vitamin that contains a metal atom

vitamin B12 (cobalamin)

only microorganisms can produce this vitamin. It cannot be made by plants, animals, birds, or humans

vitamins A, D, E, and K

fat-soluble vitamins

fat-soluble vitamins

Their structures as a whole are nonpolar, which enhances their solubility in cell membranes.

vitamin A

important for vision, cell differentiation, epithelial tissue maintenance, and growth

Preformed Vitamin A (Retinoids) and Provitamin A (Precursors)

Two forms of vitamin A

• Retinol

• Retinal

• Retinoic acid

Retinoids include:

carotenoids

plant pigments that serve as precursors of vitamin A

beta-carotene

main carotenoid that can form two molecules of vitamin A

vitamin A

function (vision) - retinal + opsin forms rhodopsin, which converts light into nerve impulses

vitamin A

function (cell differentiation) - retinoic acid regulates gene expression and helps immature cells become specialized

vitamin A

function (epithelial tissue) - keeps skin and linings healthy and prevents dryness and hardening

vitamin A

function (growth and reproduction) - needed for sperm development and fetal development

• vitamin D₂ (ergocalciferol)

• vitamin D₃ (cholecalciferol)

2 vitamin D forms

vitamin D₃ (cholecalciferol)

produced in the skin by sunlight (UV light) from 7-dehydrocholesterol

vitamin D₂ (ergocalciferol)

produced from ergosterol (plant sterol) and is also formed through light exposure.

vitamin D

maintains calcium and phosphate levels and supports bone health

vitamin D

activation undergoes two hydroxylation steps in the liver and kidneys to form the active form

vitamin D

sources of this vitamin - liver, fatty fish, egg yolks, fortified foods, and sunlight exposure

vitamin E

antioxidant that prevents the oxidation of polyunsaturated fatty acids in membrane lipids

vitamin E

protects vitamin A from oxidation

alpha-tocopherol

the tocopherol form with the greatest biochemical activity

beta-tocopherol

analogue of vitamin E that exhibits antioxidant properties and can inhibit melanin synthesis

gamma-tocopherol

main form of vitamin E in foods with antioxidant and anti-inflammatory properties

delta-tocopherol

found in maize oil and soybean oils and acts as plant metabolite and food antioxidant

vitamin E

sources of this vitamin - plant oils, green leafy vegetables, and whole grains

vitamin K

essential for blood clotting and formation of prothrombin and at least five other proteins

vitamin K

required for the formation of prothrombin and other proteins

vitamin K

required for biosynthesis of proteins in plasma, bone, and kidney

vitamin K1 (phylloquinone)

vitamin K found in plants and contains one C=C bond

vitamin K2 (menaquinones)

vitamin K found in animals and humans and can be synthesized by bacteria

vitamin K

sources of this vitamin - leafy green vegetables such as spinach and cabbage