HN exam 3
Selenocysteine
considered the 21st amino acid, there is a codon that directs the insertion of selenocysteine into selenoproteins
catalase
converts hydrogen peroxide (an ROS) to water and oxygen - uses Iron (Fe) as a cofactor
superoxide dismutase
converts superoxide to peroxide (neutralizes superoxide which is a ROS) - uses copper, zinc, and manganese for cofactors
Which of the following is not a reason that alcoholics develop Wernicke-Korsakoff Syndrome? a) Excretion of more thiamin b) Decreased hepatic thiamin pyrophosphate formation c) Drinking alcohol instead eating foods containing thiamin d) All of the above contribute
d) all of the above are reasons that contribute to Wernicke-Korsakoff Syndrome
Which of the following is not a function of biotin? a) Histone biotinylation b) Gluconeogenesis c) Amino acid breakdown d) Biotin is needed for all of these functions e) Fatty acid synthesis
d) biotin is needed for all of these functions
enzymes that metabolize thyroid hormone
deiodinases - there are three (type 1, 2, and 3) that are selenoenzymes
Dietary guidelines vs Dietary reference intake (DRI)
dietary guidelines: provide qualitative advice to the public about diet and chronic disease prevention and maintaining health. DRIs: provide quantitative advice to professionals about amounts of nutrients or food components to be of benefit.
synthetic alpa-tocopherol
dl-alpha-tocopherol - racemic (equal) mixture of all the different possibilities
Which of the following is not a function of PLP? a) Transamination b) Glycogenolysis c) Heme Synthesis d) Niacin Synthesis e) Glycolysis
e) Glycolysis
Which of the following is/are epigenetic modification(s) that results in decreased gene transcription? a) Both DNA demethylation and histone acetylation b) DNA demethylation c) Histone acetylation d) DNA methylation e) Both DNA methylation and histone deacetylation f) Histone deacetylation
e) both DNA methylation and histone deacetylation - both result in decreased gene transcription
Which of the following is not a condition that people commonly take high supplemental vitamin B6 levels that might result in toxicity symptoms? a) Carpal Tunnel Syndrome b) Premenstrual Syndrome c) Morning Sickness d) All of the conditions are ones that supplemental vitamin B6 is taken for e) Eye dryness
e) eye dryness - not a condition that people usually take vitamin B6 for
Which of the following is manganese not a cofactor for? a) Urea cycle enzyme b) Superoxide dismutase c) Gluconeogenesis enzymes d) Proteoglycan enzymes e) Glycolysis enzyme
e) glycolysis enzyme
EAR
estimated average requirement - requirement for 50% of the population - need to have research available to set so won't always be able to have an EAR - higher risk of inadequancy than RDA (0.5 or 50%) - loewr value than the RDA
Chilean miners
exposed to Mn-containing dust --> manganese toxicity
deficiency of manganese
extremely rare not much known but: - reduced growth - vomiting - dermatitis - changes in hair color - skeletal defects
manganese toxicity
extremely rare - neurological abnormalities/disorders such as schizophrenia and Parkinson's disease *may be associated with iron deficiency because low iron levels allow for increased absorption of Mn
vitamin E deficiency
extremely rare - primarily occurs in people with lipid malabsorption problems or Ataxia with Isolated Vitamin E Deficiency (AVED) - primary symptoms: neurological problems
"factor A" and "factor B" in early vitamin discovery
factor A: - fat soluble - deficiency resulted in severe ophthalmia (inflammation of the eye) - vitamin A factor B: - water soluble - deficiency resulted in beriberi - vitamins B1 and B2
T/F I have more confidence in an AI than an RDA to meet a person's nutrient needs.
false since the AI is not based on research and the RDA is
T/F The primary cofactor formed from vitamin B6 is pyidoxamine phosphate, which has to be dephosphorylated before it is taken up.
false. The primary cofactor formed from vitamin B6 is PYRIDOXAL phosphate, which has to be dephosphorylated before it is taken up.
T/F An AI falls between the EAR and UL.
false. we don't know where the AI falls since there isn't an AI and EAR
tropocollagen
fibrous protein consisting of three strands twisted together
antioxidant vitamins and minerals
*Vitamin E* *Vitamin C* Riboflavin *Selenium* Iron Copper Zinc Manganese * Primary function is as an antioxidant
PLP (pyridoxal phosphate) functions
*cofactor form of vitamin B6 *it is a cofactor for over 100 different enzymes, mostly in amino acid metabolism - transamination - some deamination - glycogenolysis - NT synthesis - heme synthesis - involved in synthesis of niacin from Tryptophan
decarboxylation reactions that thiamin (TPP specifically) serves as a cofactor for
*result in loss of CO2 - transition reaction - one reaction in the Citric Acid Cycle
functions of vitamin c
- Antioxidant - Synthesis of collagen - Prevents the disease scurvy - carnitine synthesis - tyrosine synthesis and metabolism - seratonin synthesis - other hormone and NT synthesis
Goitrogen-containing foods
- Cassava - Millet - cruciferous vegetables - onions - garlic - soybeans - peanuts
DRI components
- Estimated Average Requirement (EAR) - Recommended Daily Allowance (RDA) - Adequate Intake (AI) - Tolerable Upper Intake Level (UL)
biotin absorption
- free biotin is highly absorbed - an enzyme cleaves the lysine off the biocytin for it to be absorbed - free biotin is taken up by the sodium-dependent multivitamin transporter (SMVT)
riboflavin absorption and excretion
- highly absorbed in free form (other forms must be cleaved or converted before absorption) - excreted primarily in urine (It is water-soluble)
Biotin functions
- important cofactor for carboxylase enzymes (add carboxylic acid groups) - ex. in fatty acid synthesis and in the oxaloacetate workaround of gluconeogenesis - histone biotinylation - AA breakdown - treatment for brittle nail syndrome
Niacin flush
- main symptom of Niacin toxicity - a temporary tingling sensation due to dillation of capillaries - Nicotinic acid ONLY - a nicotinic Acid receptor GPR109A can mediate niacin flush side effects
ascorbic acid transport using SVCT 1 or 2
- mechanism for tissue vit. c accumulation 1. SVCT 1 and SVCT 2 transport ascorbic acid or ascorbate into the cell against the concentration gradient **Like absorption, this uptake is driven by the action of sodium-potassium ATPase. This mechanism is saturable, meaning that at high concentrations it reaches a threshold where it cannot take up ascorbic acid any faster. Thus, there is a limit to how much can be taken up through this mechanism.
ascorbate recycling
- mechanism for tissue vit. c accumulation 1. ascorbic acid is oxidized to dehydroascorbic acid (DHA). 2. DHA is then transported into the cell moving with its concentration gradient using GLUT1 or 3. 3. Once inside the cell, DHA is reduced back to ascorbic acid, thus maintaining the DHA gradient. **As a result, the cell is able to accumulate high levels of ascorbic acid
Pantothenic Acid absorption and excretion
- most pantothenic acid in food is found as CoA, which is cleaved prior to absorption - then taken up into the enteroxyte through the sodium-dependent multivitamin transporter (SMVT) - approx. 50% is absorbed - excreted primarily in urine
absorption of niacin
- mostly well absorbed - in corn, wheat, and certain cereal products niacin bioavailability is low --> some niacin is tightly bound making it unavailable or. absorption, so need to treat the grains with a base to free the niacin and allow it to be absorbed
meaningful antioxidants
- need to have a SUFFICIENT AMOUNT of the antioxidant in the RIGHT LOCATION - can't be redundant (aka there is another antioxidant system that is able to quench the same ROS) *if there is more of something in the body (tissues in particular), it is more meaningful
nicotinic Acid receptor GPR109A
- present in Adipose and Immune cells - mediates niacin flush side effects - but does not appear to mediate the lipid profile benefits by niacin
Niacin toxicity
- rare - "Niacin flush" is the main symptom reported - GI distress and Liver damage
activation of all three forms of vitamin B6
all three forms can be activated by being phosphorylated - these phosphorylated forms can be interconverted to the active/cofactor form of vitamin B6 which is pyridoxal phosphate (PLP) ***FMN catalyzes this reaction
Pantothenic Acid functions
coenzyme A - SO many since acetyl-CoA is a central point in metabolism 1) Beta oxidation 2) De novo lipogenesis 3) Acyl carrier protein
Ataxia with Isolated Vitamin E Deficiency (AVED)
individuals with AVED have a mutation in their alpha-TTP that prevents it from functioning correctly
Chronic Disease Risk Reduction Intake (CDRR)
intake that there is evidence reduced the risk of chronic disease - only one set for sodium currently
_______ and ______ are important in the synthesis and metabolism of thyroid hormone.
iodine and selenium
Goiter
iodine deficiency, enlargement of the thyroid to help increase its ability to take up iodine
catalase cofactor
iron (Fe)
chiral centers in alpha-tocopherol
it has three, 2' 4' and 8'
is vitamin C stored in the body?
it is not stored but it is accumulated in certain tissues in the body
transketolase
key enzyme in the pentose phosphate pathway Requires *thiamine*.
how are selenium levels in the body regulated?
levels in the body are regulated by urinary excretion, not absorption
vitamin E excretion
major route: through bile that is then excreted in feces second route: in the urine after vitamin E is chain-shortened in a process similar to beta-oxidation to make them more water-soluble
collagen
makes up 30% or more of total body protein - collagen strands cross link (by hydroxyls) to form tropocollagen
Linus Pauling
prescribed megadoses of vitamin C for the common cold (but most excess vitamin C is excreted out as urine)
absorption and excretion of manganese
pretty low absorption (<5%) excreted primarily in bile --> feces (*unique)
excretion of vitamin B6
primarily excreted in urine (water-soluble)
selenium excretion
primarily in urine - if high amounts of selenium it can be expired (breathed out) which causes a garlic odor
best food sources of vitamin E
primarily oils and nuts - primarily alpha and gamma-tocopherol
What two post-transcriptional enzymes in collagen synthesis require ascorbic acid to function properly?
prolyl and lysyl hyroxylases because they need Fe2+ and ascorbic acid regenerates Fe2+ from Fe3+
dietary guidelines
provide qualitative advice to the public about diet and chronic disease prevention and maintaining health.
Primary circulating forms of vitamin B6
pyridoxal and PLP
macrominerals, trace minerals, ultratrace minerals
quantities: macrominerals>trace>ultratrace macro minerals: need the most of (need in greater quantities) ultratrace minerals: need very small quantities of
vitamin B6 deficiency
rare symptoms: - skin or scalp ailments - microcytic hypo chromic anemia (small cells, low color) --> due to decreased heme synthesis - neurological symptoms as a result of decreased NT synthesis (convulsions, depression, confusion)
iodine toxicity
rare but like iodine deficiency, can result in thyroid enlargement, hypothyroidism, or hyperthyroidism
selenium toxicity
rare in humans - symptoms: nausea, fatigue, diarrhea, hair 7 nail brittleness, rash, nervous system abnormalities - can happen in animals due to runoff (around a body of water in an area with high selenium levels --> this works its way up the food chain)
why shouldn't you consume raw eggs?
raw egg whites contain a protein called avidin which binds biotin and prevents its absorption
selenium absorption, is one form absorbed more than another?
readily/highly absorbed organic forms (selenomethionine for ex.) are absorbed more than inorganic forms (such as selenite)
RDA
recommended daily allowance - meets needs of 97.5% of the population - set using EAR (so research is needed) - risk of inadequacy is 0.025 (2.5%) - RDA=EAR + 2 standard deviations
RDI
recommended daily intake - used on food labels, not a DRI component
thyroid hormone
regulates the basal metabolic rate, important for growth and development especially in primarily of fetus or infant
alpha-tocopherol transfer protein (alpha-TTP)
responsible for maintaining higher levels of alpha-tocopherol in the body - preferentially binds to 2R alpha-tocopherol (2' chiral center is in R confirguration) and helps facilitate its incorportation into VLDL
what micronutrient is photosensitive?
riboflavin --> destroyed by light (used to be a problem when milk was delivered in glass bottles)
Iodine is critical for the synthesis of ____
thyroid hormones *its only (yet critical function)
difference between tocopherols and tocotrienols
tocopherols: have a saturated tail tocopherols: unsaturated tail
______ can be used to form Niacin
tryptophan - kynurenine intermediate - niacin equivalents (NE) were created by the DRI committee to account for theamount of niacin in foods as well as their tryptophan content
International Unit (IU)
unit used to describe the bioactivity of different compounds, including 4 vitamins: A, D, E, C - commonly used for supplements, not common for food items
Reactive Oxygen Species (ROS)
unstable oxygen-containing molecuel that seeks out other compounds to react with
selenoenzymes
used to describe the subset of selenoproteins that are enzymes - contain selenocysteins as an amino acid in the active site of the enzyme (not external) - selenium therefore does NOT serve as an external cofactor like most minerals
Thiamin
vitamin B1 - heat-sensitive - primary part of Factor B so was one of the original vitamins
vitamin c importance for collagen
vitamin C is needed for proline hydroxylase and lysyl hydroxylase to carry out their catalytic function. - these hydroxylases need Fe2+ and ascorbic acid regenerates Fe2+ from Fe3+, allowing the enzymes to continue to hydroxylate proline and lysing
antioxidant network step 1
vitamin E cycle - alpha-tocopherol is oxidized by donating an electron to a ROS, stabilizing it - alpha-tocopherol radical is formed
how is vitamin E absorbed
vitamin E is fat-soluble so all fat-soluble vitamins are handles like lipids --> incorporated into chylomicrons that have triglycerides removed by LPL - chylomicron remnants containing vit. E are then taken up by the liver
epigenetics
"above the genome" -how genes are expressed
Vitamin B6 toxicity
***it can produce toxicity, unlike many of the B vitamins - neurological damage - people self-treating may go above this
Pantothenic Acid deficiency
- very rare - "burning foot syndrome" - vomiting, fatigue, weakness, restlessness, irritability
Biotin deficiency
- very rare - skin rash, hair loss, neurological disturbances - could be the result of raw egg consumption or biotinidase mutation (can't cleave biocytin for absorption)
Vitamin E toxicity
-rare -high levels of intake of alpha-tocopherol (supplements) are associated with decreased blood coagulation due to potential anti-vitamin K activity
tryptophan accounts for ___% of amino acids in protein
1% (so take amount of protein x.01)
functions of FAD and FMN
1) CAC: FAD reduced to FADH2 2) Electron Transport Chain : FADH2 is used to produce ATP (complex 1 includes an FMN molecule) 3) Fatty Acid Oxidation (Beta-Oxidation) : FAD is reduced to FADH2 4) Niacin synthesis from tryptophan: FAD required 5) Vitamin B6 activation : FMN needed 6) Neurotransmitter Catabolism: FAD required 7) Antioxidant enzymes: FAD required
DRIs
Dietary Reference Intakes provide quantitative advice to professionals about amounts of nutrients or food components to be of benefit. - collective term to refer to EAR, AI, RDA, UL, CDRR, profe
Goitrogens
Dietary compounds that interfere with thyroid hormone production or utilization - not clinically importance unless there is a coexisting iodine deficiency - Cassava, Millet, Cruciferous vegetables, onions, garlic, soybeans, peanuts
a) form of vitamin B6 in animal products b) form of vitamin B6 in plant products
a) found in its cofactor forms in animal products: Pyridoxal Phosphate (PLP) or pyridoxamine phosphate (PMP) b) in plants it is primarily found as pyridoxine glucoside (has a glucose added to it)
a) Thiamin form found in plants b) Thiamin form found in animals
a) free thiamin b) thiamin pyrophosphate (TPP) - phosphates must be cleaves before thiamin is taken up into the enterocyte
Which of the following is not a function of PLP? a) Glycolysis b) Transamination c) Niacin Synthesis d) Glycogenolysis e) Heme Synthesis
a) glycolysis
functions of thiamin
1) Cofactor for decarboxylation reactions (TPP) 2) Cofactor for the synthesis of pentoses (5-carbon sugars) and NADPH (TPP) by TRANSKETOLASE 3) Membrane and nerve conduction (Not as a cofactor) - as thiamin triphosphate (TTP)
symptoms of Pellagra
1) Dementia 2) Dermatitis 3) Diarrhea
what cofactors is riboflavin important in the production of?
1) Flavin adenine dinucleotide (FAD) --> add two hydrogens for it to become FADH2 2) Flavin mononucleotide (FMN) - only contains one phosphate group and doesn't have the ring structures off of the phosphate like FAD
what forms of vitamin E are absorbed the best?
all forms of vitamin E (tocopherols, tocotrienols) are absorbed equally
where is most vitamin E found in the body
in the adipose tissue
where is most absorbed iodine accumulated?
in the thyroid, which keeps it for use to synthesize thyroid hormone
ORAC (Oxygen radical absorbance capacity)
in vitro antioxidant assay - does not take into account important factors such as bioavailability - no evidence that a high ORAC score leads to any benefit in vivo - not really used anymore
niacin cofactors
1) Nicotinamide Adenine Dinucleotide (NAD) --> NADH 2) Nicotinamide Adenine Dinucleotide Phosphate (NADP+) --> NADPh
3 compounds that compose vitamin B6
1) Pyridoxine - has alcohol group 2) Pyridoxal - has aldehyde group 3) pyridoxamine - has amine group
How to calculate the Niacin Equivalents
1) amount of protein x.01 = amount of tryptophan (in g) 2) convert g of tryptophan to mg by x 1000mg/g 3) divide mg of tryptophan / 60mg of tryptophan this is 1 NE, to get the NE from tryptophan 4) add the mg of niacin to the NE of tryptophan for total NE
two causes of biotin deficiency
1) biotinidase mutation - can't cleave biotion from biocytin for absorption 2) raw egg consumption
conditions that vitamin B6 supplementation may be used for
1) carpal tunnel syndrome 2) morning sickness 3) PMS
2 primary dietary forms of biotin
1) free biotin 2) biocytin (biotin + lysine)
Pantothenic acid roles in the body
1) it is part of coezyne A (coA) - its major role 2) part of acyl carrier protein
Niacin forms
1) nicotinic acid 2) nicotinaminde
Cofactor forms of vitamin B6
1) pyridoxal phosphate (PLP) - primary form 2) Pyridoxamine phosphate (PMP)
manganese serves as a cofactor for ____
1) superoxide dismutase (superoxide --> hydrogen peroxide) 2) gluconeogenesis oxaloacetate workaround enzymes 3) urea cycle enzyme 4) enzymes critical to proteoglycan production (essential component of cartilage and bone)
Keshan Disease
A heart disorder caused by selenium deficiency. - mostly in mountainous regions of China - causes heart lesions
avidin
A protein in raw egg whites that binds biotin and prevents its absorption - cooking denatures this protein - need to consume a very large amount for it to result in a biotin deficiency
Which of the following is not true about riboflavin? a) It is primarily excreted in feces b) Only free riboflavin is taken up c) It is used in FAD and FMN d) It is yellow in color e) It is sensitive to light
a) is NOT true - since riboflavin is water soluble it will primarily be excreted in urine
mechanisms for tissue vitamin C accumulation
1. ascorbic acid transport using SVCT 1 or 2 2. Ascorbate recycling
two main epigenetic modifications
play a major role in determining what genes are expressed 1) DNA methylation 2) Histone modification
Which of the following is not true about thiamin? a) The primary cofactor form is thiamin phosphate b) There is little storage of it c) It is heat-sensitive d) Phosphates must be cleaved from it before uptake
a) is NOT true - the primary cofactor is thiamin pyrophosphate (TPP)
how many free radicals can ascorbic acid stabilize or quench?
2 free radicals
what does alpha-TTP preferentially bind to?
2R alpha-tocopherol, meaning any alpha-tocopherol where the 2' chiral center is in R configuration
fat soluble vitamins
ADEK
Which function of thiamin does not involve thiamin pyrophosphate (TPP)? a) Membrane and nerve conduction b) Pentoses and NADPH synthesis c) Decarboxylation reactions d) All of the above involve TPP
a) membrane and nerve conduction involves thiamine triphosphate (3 phosphates instead of 2)
ascorbic acid absorption
actively absorbed by the sodium vitamin C cotransporter 1 (SVCT 1) -> ascorbic acid then diffuses in to the capillary and ultimately enters general circulation
absorption of Vitamin B6
75% absorbed, through passive diffusion **PLP and PMP are dephosphorylatedbefore uptake into the enterocyte to get free pyridoxine BUT some pyridoxine glucoside (plant storage form) is absorbed intact
why in the Keshan disease experiments did the selenium-adequate mice developed heart pathology after being exposed to the coxsackie virus isolated from selenium-deficient mice.
In experiments the increased oxidative stress in the selenium-deficient mice caused mutations in the coxsackie virus which made it more virulent. The virus was then able to cause the heart pathology that occurs in Keshan disease in selenium-adequate mice. This suggests that without selenium, selenoenzymes that are antioxidant enzymes, are not able to function adequately leading to the effects described above.
water soluble vitamins
B vitamins and C vitamins
vitamin B7
Biotin
superoxide dismutase cofactors
Cu, Zn, Mn
dry beriberi vs wet beriberi
Dry: Nervous system; loss of muscle function, numbness, and/or tingling Wet: CV system; pitting edema, heart enlargement
T/F Thiamins only function is as a cofactor
False. Thiamin Triphosphate (TTP) functions in membrane and nerve conduction.
Do most Americans get enough Iodine? through what form?
For most Americans, we consume ample iodine through the consumption of iodized salt. Consumption of 1/2 teaspoon of iodized salt meets the RDA for iodine (easy to meet RDA)
form that iodine is primarily found in foods as
Iodide (I-) *iodide concentrations of the soil vary greatly (like selenium), which causes food concentrations to greatly fluctuate
selenium deficiency
Keshan disease
Potassium iodide (KI) or potassium iodate (KIO3) for salt iodization
Potassium iodide (what the US mainly uses) - less expensive - higher iodine content - more soluble Potassium iodate - more stable
can minerals be synthesized in the body?
NO. They cannot be synthesized in the body, are essential in diet for body functions
how is an RDA set?
RDA= EAR + 2 standard deviations
Vitamin B3
Niacin
Pellagra
Niacin deficiency - rare in US but it was common in early 1900s - occurs in population that consumes only corn (bc low bioavailability) - symptoms: 3D's
primary circulating form of Niacin
Nicotinamide
what micronutrient can improve people's lipid profiles?
Nicotinic Acid when it is consumed at levels far above the RDA --> however this hasn't been shown to decrease CV disease risk
Without _____, all amino acids would be essential because we would not be able to synthesize nonessential amino acids.
PLP (pyridoxal phosphate) - cofactor form of vitaminB6
histone acetylation
addition of an acetyl group to the histone --> causes the DNA structure to open up so that transcription can occur
histone biotinylation
addition of biotin to the histone - rare
AI
adequate intake -- used when insufficient evidence exists for EAR, RDA -- level that looks to be adequate in a defined population or subgroup -- it is unknown how an AI quantity compares to a RDA/EAR
gene in a tale of two mice
agouti gene : methylation --> gene suppressed --> mouse has a dark coat and is thinner (yellow & fat is the result when the gene isn't methylated)
James Lind
Prescribed lime juice containing vitamin C to prevent scurvy in 1795 - they thought citrus fruits helped due to the acidity
Vitamin B6
Pyridoxine
which is accurate for a larger percentage of the population: EAR or RDA?
RDA RDA is adequate for 97.5% of the population, it is a higher value than the EAR EAR is adequate for 50% of the population
natural alpha-tocopherol
RRR-alpha-tocopherol - all 3 chiral centers are in the R position
______ is high in iodine, thus foods of ______ origin are good dietary sources of iodine
SEA WATER is high in iodine, thus foods of MARINE origin are good dietary sources of iodine *diary products are also good sources because it is added to cattle feed and cattle receive iodine containing medications and iodide containing sanitizing solutions
Primary circulating form of thyroid hormone is ___? Active form of thyroid hormone is ___?
T3 (triiodothyronine) is the ACTIVE form T4 (thyroxine) is the primary circulating form, is converted to T3
pyridoxal phosphate (PLP)
The active coenzyme form of vitamin B6 - has a phosphate group added in place of a hydroxyl group
DNA methylation
The addition of methyl groups to bases of DNA after DNA synthesis; decreases gene transcription --> demethylation increases gene transcription
cofactor for the enzyme transketolase
Thiamin Pyrophosphate (TPP)
cofactor form of thiamin
Thiamin Pyrophosphate (TPP) - thiamin + 2 phosphates - phosphates must be cleaves before thiamin is taken up into the enterocyte
THTR-1 and THTR-2
Thiamin transporters - THTR-1: found on the brush border and basolateral membrane (going into circulation) - THTR-2: found only on the brush border
vitamin C forms
a) ascorbic acid or ascorbate (reduced form) b) dehydroascorbic acid or dehydroascorbate (oxidized form) --> semidehydroascorbate is formed when there is only 1 degree of oxidation (dehydroascorbate is 2 degrees of oxidation)
US vitamin E consumption vs europe vitamin E consumption
US consumes more gamma-tocopherol (from soybean oil) and Europe consumes more alpha-tocopherol (from olive, sunflower, and canola oil) but in the serum concentrations are roughly the same
storage of thiamin
Very little, like most water-soluble vitamins
scurvy and its symptoms
Vitamin C deficiency symptoms: - bleeding gymns - pinpoint hemorrhages - corkscrew hairs - easy bruising - impaired wound and fracture healing ***these occur bc insufficient Fe2+ since vit. C isn't regenerating it --> collagen isn't being hydroxylated enough to form sufficient tropocollagen --> collagen is being degraded
Iodine absorption
Well-absorbed (90%)
do americans get enough micronutrients?
a large percentage of americans don't meet the EAR for vitamin E, magnesium, vitamin A, and vitamin C
glutathione peroxidase
a selenium-containing enzyme that protects cells from oxidative damage by neutralizing peroxides - converts hydrogen peroxide to water
Which of the following is not a function of FAD? a) Vitamin B6 activation b) Fatty acids oxidation c) Antioxidant enzymes d) Niacin synthesis e) Citric acid cycle
a) Vitamin B6 activation is not a function of FAD because FMN is used
main form of vitamin E
alpha-tocopherol
what happens if there isn't research to set an EAR?
an AI (adequate intake) is set.
Niacin functions
approx. 200 enzymes require NAD or NADP+ - glycolysis - CAC - B-oxidation - Alcohol metabolism - de novo lipogenesis
Riboflavin deficiency
ariboflavinosis - rare - tongue inflammation (glossitis) - skin inflammation - lesion/cracking of corners of the mouth
antioxidant network step 2
ascorbate is oxidized to form dehydroascorbate. This regenerates alpha-tocopherol from alpha-tocopherol radical *known as the vitamin C cycle since ascorbate is vitamin C
antioxidant network step 3
ascorbate is regenerated from dehydroascorbate by the selenoenzyme thioredoxin reductase. *known as the selenium cycle
what form does Vitamin C generally circulate as?
ascorbic ac
primary form of vitamin C in food
ascorbic acid (80-90%) and dehydroascorbic acid (10-20%)
Which of the following is not a major function played by selenoproteins? a) Antioxidant enzymes b) Tropocollagen production c) Thyroid hormone metabolism
b) Tropocollagen production
why does the level of selenium in foods vary?
because the amount of selenium in food varies based on soil selenium levels
thiamin uptake and absorption - passive or active
believed to be an efficient process - passive when thiamin intake is high - active when thiamin intake is low - 2 thiamin transporters (THTR 1 and 2) are involved in thiamin uptake and absorption
Riboflavin color
bright yellow
Which of the following is the major function of pantothenic acid? a) Fluid Balance b) Acyl Carrier Protein c) Coenzyme A (CoA) d) Electron Transport Chain
c) Coenzyme A (CoA)
histone deacetylation
causes the DNA to become more tightly packed, preventing transcription from occuring
histone modification
changes in the structure of histones that make it more or less likely that a segment of DNA will be transcribed - acetylation is most common
problems that can arise from free radicals
free radicals/ROS can oxidize a) LDL (cholesterol carrier) which can lead to atherosclerosis b) proteins which can lead to cataracts c) DNA which can cause mutations and lead to cancer
riboflavin form in food
free, protein-bound, or in FAD or FMN **only free riboflavin is taken up so it must be cleaved or converted before absorption
bioavailability of vitamin C
high at lower doses, drops to less than 50% at higher doses
should you take high doses of antioxidants?
high doses of antioxidants may cause more harm than good - a U shape curve going from deficiency --> toxic
why might high vitamin C intake contribute to kidney stones?
high intake of vitamin C increases excretion of uric acid and oxalic acid, which are the primary components of 2 types of kidney stones - but link not been formally established
bioavailability
how much of a compound is absorbed or reaches circulation
what is unique about humans and vitamin C?
humans are one of the few mammals that do not synthesize vitamin C, making it an essential micronutrient - primates, guinea pics also do not
hydroxylases role in collagen cross-linking
hydroxylate the individual collagen strands so that they can crosslink to form tropocollagen
alpha-tocopherol derivatives
manufacturers add compounds to alpha-tocopherol through ester bonds to protect the antioxidant function of apha-tocoperhol in foods and during digestion - cleaved prior to absorption in the small intestine by esterases
free radicals
molecule with an unpaired electron in its outer orbital - this electron actively seeks an electron to stabilize itself
selenomethionine
most common organic form of selenium in plants - the sulfur in methionine has been substituted for selenium - in cereal grains such as wheat, corn, and rice and in soybeans - accumulates in the body at higher levels because it is nonspecifically incorporated in place of methionine!!
will there ever be an AI and RDA for the same population class?
no, an AI is only set if there isn't research to set an EAR
is vitamin B6 heat stable?
no, it can be destroyed during cooking or heating
are soybean, corn, and flaxseed oils considered good sources of vitamin E?
no, these are good sources of gamma-tocopherol. The DRI for vitamin E only counts 2R forms of alpha-tocopherol to be good sources
is a macromineral more important than an ultratrace mineral?
no, these names are only to do with the quantities needed not the importance
Pantothenic Acid toxicity
none
Riboflavin toxicity
none
thiamin toxicity
none
biotin toxicity
none known
are water-soluble vitamins stored in the body?
not generally
do megadoses of vitamin C reduce the risk of the common cold?
not in most people but it might benefit people exposed to brief periods of severe physical exercise (marathon runners) or cold environments
Vitamin C toxicity
not really toxic bc water-soluble for some people if they have a lot: GI distress, diarrhea - increased vitamin C intake might contribute to kidney stones
forms of vitamin E that count for the Dietary Reference Intake (DRI)
only 2R forms of alpha-tocopherol because these forms bind to alpha-TTP - unit: mg alpha-T
organic vs inorganic selenium
organic forms: contain carbon - selenomethionine, selenocysteine inorganic forms: do not contain carbon - selenite and selenate - not usually found alone, usually complexed with sodium to form sodium selenite and sodium selenate
deficiency of vitamin C
scurvy
Keshan Disease results from a deficiency in _____
selenium
What micronutrient is involved in the metabolism of thyroid hormones through deiodinases?
selenium diodinases are selenoenzymes, so selenium is important for thyroid hormone metabolism
is selenomethionine or selenocysteine incorporated into the body at higher levels?
selenomethionine because it is nonspecifically incorporated in place of methionine (just inserted where methionine would be)
cretinism
severe hypothyroidism (from iodine deficiency) resulting in physical and mental stunting
Niaspan
slow release Nicotinic acid to help prevent toxicity symptoms - used to get the benefits for blood lipid profile
exogenous free radical sources
sources from outside of the body - UV light, radiation, smoking, inflammation, air pollution
natural vs synthetic alpha-tocopherol
stereochemistry differs between the forms - natural: all 3 chiral centers are in the R confirmation (RRR) - synthetic: racemic (equal) mixture of all the different possibilities at the three chiral centers
what is seleniums antioxidant function due to?
the action of selenoenzymes
what happens to collagen when there is inadequate vitamin C?
the collagen is under-hydroxylated because Fe2+ isn't being sufficiently regenerated for use by hydroxylases. - the collaged is therefore degraded because it can't sufficiently cross-link to form tropocollagen
difference between alpha, beta, gamma, and delta
the difference is the methyl groups on the ring
Keshan disease experiment
the group of mice that was fed a selenium deficient diet was infected with coxsackie virus that was avirulent& virulent --> this caused severe heart pathology and then the coxsackie virus turned into mostly virulent due to the oxidative stress
oxidative stress
the imbalance between the production of reactive oxygen species and the body's ability to quench them - when you have more free radicals and ROS than your body can quench
Tolerable Upper Intake Level (UL)
the maximum daily amount of a nutrient that appears safe for most healthy people and beyond which there is an increased risk of adverse health effects - NOAEL= point where no observed adverse effects have been recorded - LOAEL= lowewst observed adverse effect level
why might nicotinic acid sypplementation not be good?
the nicotinic acid receptor appears to increase glucose uptake in the intestine --> this plus a rapid decrease in lipid levels can lead to a prediabetic state
how do manufacturers protect the antioxidant function of alpha-tocopherol in foods and during digestion?
they add compounds to alpha-tocopherol through ester bonds --> alpha-tocopherol derivatives
what happens to selenoenxymes that are antioxidant enzymes without sufficient selenium?
they are unable to function correctly - ex. coxsackie virus: oxidative stress --> mutations in virus --> more virulent *similar findings with flu and HIV
how do antioxidants work?
they reduce free radicals by donating an electron to them
beriberi
thiamin deficiency -rare in developed countries -countries where white rice is a staple food are at risk
Wernicke-Korsakoff Syndrome
thiamin deficiency found in alcoholics - problems in paralysis, involuntary eye movements, muscle coordination, mental loss, confusion
alcoholics are prone to becoming ____ deficient
thiamin deficient because: 1) alcohol displaces foods that are better sources of thiamin 2) liver damage decreases TPP formation 3) increased thiamin excretion ***Wernicke-Korsakoff Syndrome