Test 3 Flashcards
Water-Soluble Vitamins
C, Thiamin, Riboflavin, B6, B12, Folate, Biotin, Niacin, Pantothenic Acid
Fat-Soluble Vitamins
A, D, E, K
Water soluble
excrete via urine
Fat-soluble
goes through liver, bile duct, intestines, then excreted through feces
Thiamin
B1
Riboflavin
B2
Niacin
B3
Vitamin
Organic compounds that are required in the diet in only small amounts to maintain fundamental functions of the body
B6 is composed of what 3 compounds
pyridoxine, pyridoxal, pyridoxamine
Some vitamins are not strictly dietary essential:
ex: Vitamin D(cholesterol), Niacin (tryptophan), Biotin and vitamin K can be made in part by bacteria in large intestine
Can water soluble vitamins accumulate in toxic concentrations?
Rarely
Water soluble vitamins storage is limited and must be provided regularly, except for…
T; cobalamin (B12)
***When water soluble vitamins are consumed in excess of body needs, generally the excess is
Excreted in the urine
Most common function of water-soluble functions…
coenzymes or components of coenzymes
Ascorbic Acid
Vitamin C
Vitamin C is made from _____ in plants
glucose
Oxidized vitamin C becomes
Dehydroascorbic Acid (DHAA)
-it can serve as an antioxidant
Which form of vitamin C is anti-oxidant
ascorbic
Five servings of fruits and vegetables a day can provide how much Vitamin C?
Approx. 200 mg
How is ascorbic acid absorbed?
via sodium-dependent active transport in the SI
DHAA is absorbed how?
passive diffusion or glucose transporters
Bioavailability
represents the proportion of the compound that is absorbed from the GI tract
Vitamin C bioaviilability
Nearly 100% for dose between 12-200mg, which declines for higher doses (~50% for 1250 mg)
Excess AA are excreted in urine if plasma level is
HIgher than renal threshold
Renal threshold of vitamin C
-plasma level at 0.8-1.4 mg/dL
-body pool at 1500 mg
-dietary 100 mg daily
Ascorbic Acid acts as an electron donor for how many mammalian enzymes?
at least 8
Enzymes that require ascorbic acid either have ____ or ___ activity.
Monooxygenase or dioxygenase
How does vitamin C function in collagen synthesis?
AA is utilized for hydroxylation of proline and lysine residues of alpha-chains of procollagen
***Vitamin C acts as a coenzyme by maintaining iron in a reduced state in:
collagen synthesis
Vitamin C in neurotransmitter synthesis:
-synthesis of norepinephrine from dopamine
-synthesis of serotonin from tryptophan
Vitamin C in bile acid synthesis
-required for the hydroxylation of cholesterol via 7-alpha-hydroxylase, a rate limiting step of bile acid synthesis
Vitamin C deficiency
Scurvy
-<10 mg daily for months
*** As little as 10 mg/day of Vitamin C may be enough to prevent scurvy.
True
Biologically active form of Thiamin
thiamin diphosphate or thiamin pyrophosphate (same same)
Food sources of thiamin
enriched grain products, meats (especially pork), nuts
Thiamin is digested into _______ before absorption
Free form
Low concentrations of thiamin is absorbed into enterocyte via
High concentrations….
Na+-K+ pump
-passive diffusion
Within liver, ____ donates phosphate to thiamin to make it TDP (active state)
ATP
50% of thiamin in body is contained in _____
muscle tissue
Thiamin is coenzyme for
decarboxylation reactions in carbohydrate catabolism
***A major role for thiamin is:
energy transformation
Thiamin deficiency
Beriberi
Dry Beriberi
characterized by muscle weakness
Wet beriberi
characterized by heart failure
***Deficiency of thiamin may occur in alcoholics because…
alcohol prevents thiamin uptake and utilization
Riboflavin can be degraded by ____ or ____.
light or acid
Food sources of Riboflavin
milk and dairy
meats (especially organ)
eggs
broccoli, spinach, mushrooms
fortified, ready-to-eat breakfast cereals
Which two enzymes take FAD to FMN to riboflavin
FAD pyrophosphatase
FMN phosphatase
Does the brain ever experience riboflavin (B2) deficiency?
No bc brain cells uptake FAD through a high-infinity transport system so that FAD does not decline even during riboflavin deficiency
What is the primary metabolite found in urine?
Free riboflavin (60-70%)
Function of Riboflavin
FAD & FMN (as coenzymes) are donors or acceptors of hydrogen and electrons in many redox reaction
-Krebs cycle
- beta-oxidation of fatty acids
How is B2 related to folate?
FADH2 is used in the formation of active folate
_____ is required for conversion of tryptophan to niacin
FAD
How is B2 related to B6 function?
FMN is important in B6 function
***Riboflavin in required for:
-formation of active folate
-conversion of tryptophan to niacin
-function of B6
Riboflavin deficiency
-can be severe
-stunted growth and skin lesions appear
Clinical features of riboflavin deficiency:
-cheilosis-cracks on the outside of lips
-glossitis-inflammation of the tongue
-hyperemia-redness of the oral cavity
Active niacin…
NAD+ and NADP+
What form of B3 is required for the synthesis of NAD+ and NADP+
Nicotinic acid
Dietary _____ must first undergo deamination to nicotinic acid
nicotinamide
Niacin equivalent
1 mg niacin or 60 mg tryptophan
***T/F Nicotinamide, but not nicotinic acid, is the form required for the synthesis of nicotinamide adenine dinucleotide
False
Food sources of Niacin
Meat, poultry, and fish
peanuts
enriched grain products
_________ converts NAD+ or NADP+ into nicotinamide before absorption
glycohydrolase
NAD+ or NADP+ is required by about ______ enzymes
200
Most of the NADH is used to…
transfer electrons to the electron transport chain -> 3 ATP
Most of the NADPH is used in….
synthesis of cholesterol, fatty acids, deoxynucleotides, and steroid hormones
Niacin (B3) deficiency
Pellagra (rough skin)
4D of Niacin deficiency
dermatitis, diarrhea, dementia, death
Toxicity of Niacin
Nicotinic acid is prescribed in grams as a drug to lower blood cholesterol
–may cause heart abnormalities, hot flashes, skin irritations, liver damages….
UL = 35 mg/day
***How are the recommended intakes of niacin expressed (units)?
niacin equivalents (mgs)
B5
Pantothenic Acid
Food sources of pantothenic acid
meat, fish, poultry
milk and yogurt
legumes and whole-grain cereals
Pantothenic acid is typically used to synthesize _______ and _______
CoA and acyl carrier protein (ACP)
Pantothenic Acid Deficiency
burning feet syndrome, headache, fatigue, sensation of weakness
***List four water soluble vitamins that are required by pyruvate dehydrogenase complex.
-pantothenic acid
-thiamin (B1)
-niacin
-riboflavin
Vitamin H
Biotin
Food sources of biotin
liver
soybeans
egg yolk
cereals/nuts
Active form of biotin
biocytin
How many carboxylases is biocytin found?
Four
The protein _____ in raw egg white binds to biotin and prevents intestinal absorption
avidin
-can lead to deficiency
_______ can produce a small amount of biotin
Intestinal flora
Route of biotin to enterocyte…
proteins that contain biotin ->biocytin ->free biotin for absorption by enterocyte
Biotin is taken up by the enterocyte via
Na+ dependent process (requires ATP) for regular amounts
-high amounts via passive diffusion
_____% of biotin is free in the blood, but some are bound by protein
80%
_____% of biotin is free in the blood, but some are bound by protein
80%
Bioavailability is variable from _____% in corn to nearly _____% in wheat
100%; 0%
Where is biotin stored
muscle, brain, liver
***Bioavailability of biotin is near 0% from wheat.
True
***Intake of raw egg white may cause deficiency of…
biotin
Biotin is coenzyme in these 4 enzymes
-Pyruvate carboxylase
-Acetyl-CoA carboxylase
-Propionyl-CoA carboxylase
-beta-methylcrotonyl CoA carboxylase
Vitamin B6 is a group of chemicals….
6 chemical forms that are interchangeable
The most common active form of B6
Pyridoxal 5’-Phosphate (PLP)
What form of B6 is found in plant foods?
Pyridoxine (PN) or phyridoxine phosphate (PNP)
What form of B6 is found in animal products?
Pyrodoxal (PL) and pyridoxamine (PM)
Vitamin B6 must be dephosphorylated prior to absorption T/F
true
Primary absorption method of B6
passive diffusion
Once in the enterocyte B6 is re-phosphorylated
true
Bioavailability of biotin
> 90%
B6 activation requires ______
riboflavin
-riboflavin deficiency may interfere with B6 metabolism
Where is 75%-89% of B6 found?
muscle tissue
How many enzymes does PLP serve as coenzyme for?
> 100
Functions of PLP
-AA metabolism
-glycogen metabolism (required by glycogen phosphorylase)
-synthesis of heme (could lead to anemia)
-required for synthesis of niacin from tryptophan (both FAD & PLP)
-methionine cycle
-homocysteine -> cysteine
***Which of the following is one of the main functions of vitamin B6?
-transamination
B6 deficiency
hypochromic microcytic anemia
B6 toxicity
pharmaceutical dose (1-6 g/day)
sensory and peripheral neuropathy
-intake of >500 mg
folic acid:
folate:
-oxidized form in fortified form or supplements
-reduced form naturally in foods
Most folate found in portal circulation
N^5 methyl THF
Most folate in liver
THF and N^5 methyl THF
Folic acid functions
methionine cycle
Methionine cycle
-occur in cytosol
-extensive folate metabolism occurs in mitochondria
-interconversion of serine and glycine requires PLP containing enzyme (SHMT)
**Methionine cycle requires
-B6
-B12
-Folate
-Niacin
(all water soluble)
Folic Acid Deficiency
-birth defects
-megaloblastic anemia
-cancer
-hyperhomocysteinemia and vascular disease
***Which anemia is related to folate deficiency?
Megaloblastic
***To protect against birth defects, a higher RDA of folic acid has been suggested for pregnant women
True
Cobalamins
B12
Which type of anemia can B12 deficiency cause?
megaloblastic
B12 consists of a group of compounds called
corrinoids
Active forms of cobalamin
methylcobalamin, adenosylcobalamin
***B12 can only be found in…
animal products
In stomach, cobalamin can be attached to _____
Intrinsic factor (IF)
IF-cobalamin is absorbed in ____ via _____
ileum; B12 receptor (recognizes the IF)
Cobalamin is rebound by ____ that is circulated to the liver
TC-II
In the liver, free cobalamin can be stored for _______
Years
-has lowest RDA requirements b/c of this
B12 is excreted via ____ and ____
bile (mostly) and urine
Whole body turnover of B12
0.1% daily
B12 function
-cofactor for methionine synthase
-transfer of adenosine group in 2 reactions
*L-methylmalonyl-CoA mutase
-maintenance of CNS including brain and spinal chord (methionine can convert to SAM ->choline->myelin sheath)
L-methylmalonyl CoA mutase
L-methylmalonyl CoA to Succinyl CoA
*required for synthesis of heme
*important role in metab. of odd chain fatty acids
*** Why is the RDA of vitamin B12 so low?
-can be stored in liver for years
-little B12 in the body is degraded
-whole body turnover is about 0.1% daily
B12 deficiency
-usually due to inadequate absorption not intake
-megaloblastic anemia (“methyl trap” of folic acid)
-neuropathy
-high homocysteine->risk of heart disease
High dietary folate may cure megaloblastic anemia caused by:
folate deficiency, B12 deficiency
Fat soluble vitamins are similar to lipids b/c…
-absorption requires bile salts
-transported by chylomicrons
-stored in liver and fatty tissue for long periods
-eliminated slowly
-generally toxic if consumed in excess
provitamin A carotenoids can be converted to ____
retinoids
beta carotene conversion ratio
1/12
alpha-carotene or beta-cryptoxanthin conversion ration
1/24
**Formation of retinol from beta-carotene requires the presence of what B vitamin?
Niacin
____ or ____ helps Vitamin A and carotenoid absorption
meal fat or oil
________ ________ as well as ________ can diminish carotenoid absorption
Fiber intake (especially pectin); excessive vitamin E
*** Dietary fat is not very important regarding the digestion and absorption of pre and provitamin A forms
False
Most retinol is stored as _______ in _____
retinyl esters in the liver
Vitamin A functions
-vision
-cellular differentiation
-growth
-reproduction
-bone development
-immune system actions
_____ is bound to _____ to form rhodopsin in rod cells
cis-retinal and Opsin
Rhodopsin is needed to see….
black and white as well as to see at night
***Within the nucleus, retinoic acid binds to
retinoid X receptors (also retinoic acid receptors)
Ergocalciferol
D2
Cholecalciferol
D3
Vitamin D form synthesized by plants
D2
Vitamin D form synthesized by humans from cholesterol in the skin
D3
How much sun exposure is enough to prevent deficiencies
10 minutes
***About ____% of vitamin D3 is absorbed from the diet
50% via passive diffusion
Where is Vitamin D metabolized?
Liver
***circulation form of D3
calcidiol
biological half life of calcidiol
3 weeks
D3 in kidneys becomes
Calcitriol (3 hydroxy groups)
Active form of Vitamin D
calcitriol
1,25(OH)2D3
Calcitriol
Vitamin D functions
-calcium homeostasis
-promoting Ca absorption in the gut
-enhancing mobilization of Ca and phosphorous from bone
-maintaining adequate blood calcium and phosphate concentrations
-involving in bone mineralization w/calcitonin hormone (from thyroid)
***The vitamin D receptor is a member of the super family of nuclear receptors that regulates gene expression.
True
Calcitriol acts with _______ hormone to affect intestine, bone, and kidney
parathyroid (PTH)
Other Vitamin D functions
-modulation of neuromuscular and immune function
-reduction of inflammation
-modulate genes that regulate cell proliferation, differentiation, and apoptosis
-prevents rickets and osteoporosis
Vitamin E exists as _____ and ____ with each having 4 isomers (8 total)
tocopherol and tocotrienol
_______ is most active form of Vitamin E
alpha-tocopherol
______ are free in foods, but ______ are esterified
Tocopherols, tocotrienols
only ___________ is resecreted back into the blood via VLDLs
alpha-tocopherol
Where is most vitamin E (over 90%)?
adipose tissue
***What is the principle transport vehicle for vitamin E in the blood?
-lipoproteins
Vitamin E function
-antioxidant, immune function, DNA repair
***Which mechanism has been proposed but not proven as vitamin E’s principle function against disease prevention?
-Anti-oxidation
vitamin E toxicity
risk of bleeding in high doses
***For which vitamin is the tolerable upper limit set b/c of increased tendency for bleeding?
E
K1
Phylloquinone-found in green plants
K2
menaquinones- from bacteria
***What is the chemical name for vitamin K in green plants?
pylloquinone
***What is the chemical name for vitamin K in green plants?
pylloquinone
Where is vitamin k stored?
primarily in the liver
Vitamin K functions
-as a coenzyme , involved in the carboxylation of certain glutamate residues in protein…located in Gla domains which can bind to Ca…-bone mineralization, blood clotting
***As coenzyme, vitamin K is required in the carboxylation of Gla proteins by converting glutamate residues to gamma-carboxyglutamate residues?
True
How does Warfarin stop clotting
-inhibits epoxide reductase and Vitamin K reductase in the Vitamin K cycle
How many proteins have Gla domains
14
What 3 processes do Gla proteins regulate?
-blood coagulation
-bone metabolism
-vascular biology
Blood Clotting cascade
Factor X, Vitamin K and calcium activate to form Xa, Active Xa converts prothrombin to thrombin (IIa), IIa catalyzes soluble fibrinogen to insoluble fibrin, fibrin aggregates to form a polymer and stop bleeding
***Vitamin K deficiency is most often observed in
-newborns
Macrominerals
-4% of total body weight; about 25-1400 g in body
Macrominerals
Ca, Ph, Mg, Na, K, Cl, S
Most abundant macromineral
Ca (40% of total mineral mass)
***Which food group contributes the most calcium to our diet?
dairy
How much dietary calcium is absorbed?
20-50%
Blood Ca levels are tightly regulated and enhanced by_____ and _____, but decreased by ______.
PTH, calcitriol
calcitronin
PTH targets bone to stimulate _____ and depress _____ to release ionized Ca into blood
osteoclasts, osteoblasts (forming bone)
***The primary function of parathyroid hormone (PTH) is:
-to enhance blood calcium levels by taking calcium from bone
Phosphorus
6th most abundant element by weight
-2nd mineral after Ca
70% of phosphorus circulates in the blood as ___
phospholipids
***Name two minerals that are part of the bone crystal, hydroxyapatite:
Calcium, phosphorus
Which mineral is a component of ATP and creatine phosphate?
phosphorus
Which mineral is a component of ATP and creatine phosphate?
phosphorus
Is Sodium an intra or extracellular cation?
Extracellular
How much Na is absorbed
95%
3 Na transport systems
-sodium/glucose co-transport
-sodium/chloride co-transport
-sodium channels
What hormone regulates plasma levels of Na?
aldosterone
Does aldosterone increase or decrease reabsorption of sodium in the kidney?
increases
Which of the following amounts comes closest to the level of sodium typically consumed in our daily diets?
2-3 g/day
Potassium is regulated by ____
aldosterone
Aldosterone has what effect on potassium
promotes excretion
***All of the following are true about potassium except:
-it increases blood pressure
***Oral supplements of ferrous iron are available in complexes with sulfate, succinate, citrate, lactate, tartate, fumarate, or gluconate. The absorption of these nonheme iron supplements could be _____ when injested with vitamin C or other antioxidants.
-increased
Which two enzymes can oxidize iron to Fe3+ so that it can bind to transferrin?
Hephaestin and ceruloplasmin
Which two enzymes can oxidize iron to Fe3+ so that it can bind to transferrin?
Hephaestin and ceruloplasmin
Primary storage form of iron in cells
ferritin
Primary storage form of iron in cells
ferritin
***Iron deficiency is second only to _____ as the most prevalent nutrition problem in the US
obesity
***Iron deficiency is second only to _____ as the most prevalent nutrition problem in the US
obesity
Zn is a cofactor for _____ enzymes
over 200
***Among the trace minerals, which mineral participates as cofactors in the most enzyme systems?
zinc
Zinc fingers…how many transcription factors require zinc
2000
Bioavailability of copper
50%
***Excess dietary iron can decrease copper absorption.
True
What two minerals can cause oxidative damage to cells when in their free ion forms?
copper and iron
**Which mineral is an essential cofactor in the action of glutathione peroxidase (GPX) in the reduction of organic peroxides and hydrogen peroxide?
selenium
Keshan disease is associated with _____ deficiency
Selenium
