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
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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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