NFS 4271- Midterm Exam Guide - Comprehensive Notes for the exam ( 191 pages long!)
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6 Oct 2017
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NFS 4271
MIDTERM EXAM
STUDY GUIDE
Ch. 9 Water-Soluble Vitamins – B Complex
Thiamin (Vitamin B1)
● Energy production
● Amine group: pyrimidine group + thiazole ring linked by a methylene (CH2)
bridge
o Sulfur and nitrogen containing
● Thiamin pyrophosphate – coenzyme form, two phosphates (thiamin
diphosphate) TPP or TDP
● Helps body convert food into energy, and aids the function of the heart and
cardiovascular system and the brain and nervous system
● Sources: pork, whole grains, enriched cereals, liver, poultry, fish, eggs,
potatoes, legumes, nuts, dark green veggies
o Pork (3 oz)= .49 mg
o Most thiamin in human diet comes from enriched products
▪ Such products also contribute riboflavin, niacin, and iron
● in supplements, thiamin is found mainly as thiamin hydrochloride or thiamin
mononitrate salt.
● RDA:
o Men 19 and up 1.2 mg
o Female 19 and up: 1.1 mg
o pregnancy: 1.4 mg/day
o lactation: 1.5 mg/day
● Destroyed (primarily as methylene bridge) by heat and alkalinity
o cooking thiamin-rich foods in water with promote loss of the vitamin
Digestion, Absorption, Transport, and Storage
● Exists in free (nonphosphorylated) form in plant foods
● In animal foods, primarily as TPP, thiamin pyrophosphate (95%)
● Must be dephosphorylated in intestine to be absorbed as free thiamin
o intestinal phosphatases are responsible for digestion, specifically
hydrolzing the phosphates from the di-, mono-, and triphosphates
prior to absorption
o free thiamin is absorbed into intestinal cells
● Absorption is usually high
● Antithiamim factors may inhibit absorption
o Ex: thiaminases in raw fish
▪ catalyze cleavage of thiamin, destroying the vitamin
▪ cooking renders the enzymes inactive
o Tannic, chlorogenic, caffeic acids (polyhydroxyphenols)
▪ All found in coffee; interfere with thiamin absorption
▪ destroys thiazole ring
o Absorption in jejunum and illeum (some in duodenum), by diffusion
or carriers: ThTr1 and 2
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▪ carriers exchange thiamin for H+ ions as part of an antiport,
carrier system
o Ethanol interferes with absorption
▪ alcohol inhibits intestinal expression of ThTr1 and 2, and thus
thiamin absorption
o Transported free, bound to albumin, or as thiamine monophosphate
o Most thiamin in body exists as TPP (TDP)
FUNCTIONS
● Enzyme in oxidative decarboxylation (think of decarboxylation of pyruvate in
krebs cycle - carbon removal)
o Energy transformation (coenzyme role)
▪ Oxidative decarboxylation of alpha-ketoacids and 2-ketosugars
▪ Conversion of pyruvate to acetyl CoA
● Reactions in the Kreb’s cycle
o Pyruvate dehydrogenase complex: TPP
decarboxylates pyruvate to acetyl CoA
o Alpha-ketoglutarate dehydrogenase complex:
TPP decarboxylated alpha-ketoglutarate to
succinyl CoA
o ATP and Mg 2+ are required
● pyruvate + NAD+ + CoA --> acetyl-CoA + NADH + H+ +
CO2
▪ inhibition of these reactions prevents ATP synthesis and of the
acetyl CoA needed for the synthesis of fatty acids, cholesterol,
and other important compounds
● inhibition also results in accumulation of pyruvate,
lactate, and alpha-ketoglutarate
● Synthesis of pentoses and nicotinamide adenine dinucleotide phosphate
(NADPH; also a coenzyme role)
o especially active in liver
● Membrane and nerve conduction (in a noncoenzyme capacity)
● Metabolism and release of energy from carbs
● Pentose phosphate pathway
● Membrane conduction of nerve tissue
● Branched chain amino acid metabolism
Metabolism and Excretion
● excreted intact or catabolized prior to urinary excretion
Deficiency
● Beriberi
o Dry (wasting) - mostly in adults
▪ Emaciation
▪ Difficulty walking
▪ Tingling in hands and feet
▪ Loss of muscle function/paralysis of lower legs
▪ Mental confusion/speech difficulties
▪ pain
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find more resources at oneclass.com