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Nutrition

Nutr 3210

QuestionAnswer
What are the essential micronutrients for all monogastrics and birds? Vitamins A, B6, B12, E, K, thiamin, riboflavin, niacin, biotin, pantothenic acid, folate
What are the non essential micronutrients (some species)? Vitamins C (for rats, in humans-essential), D (as long as there is enough light) and choline
What are the essential macrominerals? Ca, P, Mg, Na, Cl, K
What are the essential microminerals? Fe, I, Zn, Se, Cu
What happens with iodine deficiency? metabolic rate drops, high levels of TSH cause goiter formation - hyperplasia due to thyroid attempt to put out more T3 and T4, goiter during pregnancy leads to birth defects - cretinism
What is the role of T3/T4? bind to nuclear receptors, form transcription factors which bind to response elements in promoter regions of DNA - proteins responsible for increased metabolic rate and fetal development
What is the role of vitamin A? role in visual function (night vision), retinol - bioactive form, carotene - provitamin, 'retinol activity equivalents' have similar biochem effect
What are the animal sources of vit A? retinyl esters/retinoids. liver, dairy, fish
What are the plant sources of vit A? carotenoids. brightly coloured fruits and vegetables. beta carotene has greatest provitamin A activity. denaturation in stomach - duodenum
What are the common characteristics of vit A? beta ionone ring, PU side chain, presence of functional group - alcohol=retinol, aldehyde=retinal, carboxylic acid=retinoic acid, ester=stearate or palmitate
What are the mechanisms of vit A digestion and absorption? via micelles. retinol bound to FA esters and absorbed via carrier protein. retinyl esters and carotene bound to protein and absorbed via transporters through passive diffusion.
Where are carotenoids and retinoids metabolized? in enterocytes. they are oxidized by beta carotene 15,15 oxygenase to two retinals and CRBP II reduces them to retinol. retinol is then esterified and transported to the liver in chylomicrons
Where are retinols metabolized? they are esterified in enterocytes to retinyl palmitate, incorporated into chylomicrons and transported to the liver. 70-90% of animal sources are readily absorbed
What happens when retinols reach the liver? LPL hydrolyzes the chylomicron to a remnant, releases contents in liver cell.
What happens to retinyl palmitate in the liver? retinyl palmitate can be stored in stellate or parenchymal cells. low blood [retinol] results in removal of ester and transported by RBP and TTR to the eye
What happens to beta carotene in the liver? transported out as VLDL and converted to LDL in the bloodstream to be stored in adipose tissue
What is the mechanism of converting retinol to rhodopsin? retinol oxidized to all trans retinol in retina, isomerized to 11-cis retinal, binds with opsin to from rhodopsin
What happens when rhodopsin is bleached? broken down to opsin and all trans retinal
What is retinoic acid signaling? formed in blood with individual cells and retinol. binds and activates RAR and RXR families of transcription factors to control gene expression. complexes of homo and heterodimerize fine tune variation in gene expression
What is the role of retinoic acid? differentiation, growth (bones), fertility (sperm), fetal development
What happens with retinoic acid deficiency? blindness, compromised lungs, GI tract compromised, tooth decay, birth defects (can happen when you have too much as well)
What are the sources of vitamin D? sunshine (skin), egg, milk, salmon, liver, beef, veal, fortified foods
How is vitamin D synthesized? cholesterol converted to 7-dehydrocholesterol in sebaceous glands. UVB radiation converts to lumisterol (sloughed off from skin) and previtamin D3. Thermal isomerization produces cholecalciferol (vit D3) and UVB radiation gives off tachysterol (sloughed).
What are the factors affecting vit D synthesis? latitude, skin exposure, air pollution, skin pigment
What are the mechanisms of vit D3 transport and absorption from the skin? diffuses through skin to blood, 60% bound to DBP, deposited in adipose/muscle and then goes to liver
What are the mechanisms of vit D3 transport and absorption from the diet? absorbed from small intestine lumen through BBM, packaged into chylomicrons (makes up 40% of circulating D3), transported through BLM to liver
How is cholecalciferol transformed to calcitriol? cholecalciferol is hydoxylated in liver mito. by 25-hydroxylase to calcidiol (25-OH D3) and transported to the blood via DBP. In kidney mito. hydroxylated by 1-hydroxylase to calcitriol. Carried to blood via DBP to bones, kidney and intestines.
What is the role of calcitriol? In conjunction with PTH, regulates blood Ca levels in kidney, bones and intestines.
What are the mechanisms for calcium regulation? Low Ca stimulates secretion of PTH, PTH stimulates kidneys to ^ Ca absorption & stimulates calcitriol synth. Calcitriol stimulates Ca absorption in GI. PTH and calcitriol stim. bone resorption.
How is calcitriol excreted? three potentials for metabolites to be formed and excreted in feces (<70%) or in urine. Can be hydroxylated, oxidized or side-chain cleaved.
What are the side effects of over supply of vitamin D? in children - anorexia, nausea, vomiting, renal insufficiency, failure to thrive. also can cause calcification of soft tissues (kidney, heart, lungs, blood vessels), hypertension, nausea, weakness, renal dysfunction
What will improper levels of calcidiol result in? not enough - rickets. too much - toxic
What are the symptoms of rickets? failure of bone mineralization, edema in wrists, ankles and knees, bowed legs and curved spine
What is osteomalacia? lack of vit D -> poor absorption of Ca. PTH increases, promotes bone resorption -> bones demineralize but bone mass is preserved
What is osteoporosis? low intake of Ca leads to decreased bone mass (density) but normal mineralization. Fractures are an issue.
How does aging affect vit D levels? Decreased sunlight exposure and synthesis in skin. Dietary intake is lower and absorption, hydroxylation and reabsorption is decreased.
What are the benefits of increasing vit D serum concentration? decreased fractures, improved dental health, improved lower extremity function, decreased falls, decreased risk of colorectal cancer
What are the main roles of vitamin D? precursor for formation of calcitriol, regulator of cellular function through binding of VDR, controls gene expression and cell signaling
What are the main roles of Ca? 99% localized to teeth and bones (rest in ECF for cell signaling). hydroxyapatite in bones - support and storage. If blood and ECF Ca levels drop = death, bones always compromised first.
What is the role of phosphorous? predominantly in bone, central to metabolism (ATP, DNA, RNA, IP3, cGMP, cAMP). Protein phosphorylation.
What is the main role of vitamin k? post translational modification (dependent on vit K) in proteins that need to bind Ca.
What is the role of fluoride? Forms fluorapatite, detine layer of teeth and smaller amounts of bone
Where is Ca located in body? ICF - in mitochondria and ER. ECF - half of it bound to protein. bones - <99% in mineral phase with 85% of body phosphate
What hormones manage [calcium and P]? PTH and vitamin D increase calcium. Thyroid releases calcitonin to decrease Ca.
What are the dietary factors affecting bioavailability of Ca and P? phytate from grains and legumes forms insoluble complex with Ca and prevents absorption of P. Oxalates in spinach, rhubarb and alfalfa chelate Ca and increase excretion in feces.
Why is vitamin K important? vit K mediates carboxylation of proteins and allows Ca to bind to proteins. 4 proteins involved in coagulation - factors II, VII, IX and X.
What are sources of vitamin K? Phyloquinone (K1,plants-saturated) in green leafy vegetables and oils/margarines (canola&soy). Menaquinone (K2, bacteria-unsaturated) in human colon, not suffcnt. to meet human needs. Menadione (K3, synthetic) not commonly used, liver tox. in infants
How is vitamin K absorbed? similar to vit A - absorbed in SI, brought to liver by chylomicron remnant, distributed by VLDL/LDL, little storage. status decreased by fat malabsorption
What are the mechanisms of function for vitamin K? vit K dependent gamma carboxylation of proteins - occurs on glutamic acid side chain to form gamma carboxyglutamate residues
What is the function of fluoride? fluorapatite in tooth enamel resists bacteria-induced degredation. Tooth decay if deficient.
What occurs in fluoride toxicity? Mainly cosmetic. Dusty white or mottled patches on teeth
What are the side effects of vit E deficiency? sterility in males, inability to maintain pregnancy, anemia, muscle pathology, neural defects - deficiency in selenium can also have same side effects - both involved in antioxidant defense
What are the classifications of vit E? 2 families - tocopherols (saturated) and tocotrienols (unsaturated). 4 compounds each.
What are the risks with too much intake of tocopherols? hemorrhage and heart failure. Supplements only partially active but fully contribute to UL - can take too much.
What are sources of selenium? organ meats, muscle meats, cereal.
What are the dietary forms of selenium? Selenomethionine, selenocysteine, selenite (dietary supplements). All have similar bioactivity. Selenocysteine incorporated into seleno-proteins (only 30 in total).
What are the biologically active forms of vitamin C? Ascorbic acid (reduced) and dehydroascorbic acid (oxidized)
What species need vitamin C? primates, certain small mammals (guinea pigs, fruit bats), some birds, some fish (salmon)
What are the functions of vitamin C? Hydroxylation: postranslational modification of procollagen, hydroxylation in steriod metabolisms and neurotransmitters
What are the oxidant defense mechanisms of vitamin C? blood reducing agent, limits lipid peroxidation products in urine, high levels of neutrophils may prevent overflow of oxygen radicals
What are the signs of vitamin C deficiency? hemorrhages, hair loss, loose teeth, swollen joints, poor wound healing. all related to proline hydroxylation. Scurvy.
Why is niacin (B3) important? important in ADP-phosphorylation rxns: post-translational modifications involved in DNA repair and cell signaling. tryptophan can also produce these rxns (converted to NAD) but with 1/60 efficiency. Prevents pellagra.
What are the sources for niacin? corn/maize (deficient in trytophan). Niacin is tightly bound to proteins. Must undergo alkaline treatment to be released.
What are the signs of pellagra? 4 D's: dermatitis, dementia, diarrhea, death
Why is riboflavin (B2) required? Plays a key role on metabolism of fats, ketone bodies, carbs, proteins
what are the sources for riboflavin? milk, cheese, leafy green vegetables, liver, kidney, legumes, yeast and almonds. light sensitive and low solubility.
Why is thiamine (B1) important? energy metabolism. Thiamin works with CoA, FAD & NAD to move sugars, AA, FA into aerobic metabolism and ATP production. Plays role in NADPH and ribose synth. and also in nervous transmission.
What is wet beriberi? Results from absence of TPP in pyruvate dehydrogenase and alphaKG dehydrogenase in TCA cycle. Failure of aerobic metabolism in heart. Circulatory problems and edema in limbs. Can lead to heart failure.
What is dry beriberi? Absence of TPP in nervous tissue leads to neurological symptoms. Wasting (numbness in legs), irritability and disordered thinking. Related to older age.
What is infantile beriberi? occurs at 2-5 months of age. Onset is rapid and must be treated within hours. Causes cyanosis, tachycardia and convulsions.
What is the role of pantothenic (B5) acid? Needed to form CoA and plays role in metabolism of fats, carbs, proteins. Essential to sustain life but is available in all foods.
Why is biotin (B7) important? Necessary in the TCA cycle, production of fatty acids and glucose. Necessary in ruminants to produce succinyl CoA to produce glucose. No RDA because bacteria in colon produce enough.
What is the biological importance of folate? necessary for the production and maintenance of new cells. Important in pregnancy and fetal development and in infancy. Needed to synthesize DNA bases and replication.
What does folate (B9) deficiency lead to? Hinders DNA synth, cell division, production of RBC (leads to megaloblastic anemia), neural tube defects in fetus. Affects SAM cycle
What are sources of folate? cereal, grains
What is the significance of vitamin B12? important for the function of the brain and nervous system and the formation of blood.
What are the sources for B12? bacteria (slightly spoiled food)
What are the functions of B6? transamination (pyridoxal phosphate), used in 1st step of porphyrin synthesis which leads to hemoglobin synth, and synth of neuroactive amines
Why is the SAM cycle important? methylates compounds for phosphatidylcholine, epinephrine, creatine, methylates DNA, drug metabolism
What is the importance of dTMP? DNA synthesis and cell division. shortage causes reduced DNA, diarrhea, anemia, birth defects in pregancy
What are the neuroactive amines that vit B6 synthesizes? tyrosine->norepinephrine (to epinephrine in SAM cycle), tryptophan->serotonin, histidine->histamine, glutamate->GABA
What occurs with B6 deficiency? rare - convulsions in children, microcytic anemia, dermatitis. toxicity can cause peripheral nerve damage, tingling in hands and feet
What are the sources for iron? Animal (liver, meat) gives heme iron, Fe2+ ferrous. Plant (green leafy veg, fruits, nuts) gives non heme Fe2+, Fe3+ (ferric)
How efficient is iron absorption? Varies. Heme iron is more readily absorbed than non heme and Fe3+ is not readily absorbed (vit C can reduce to Fe2+). Inhibited by chelators that form insoluble complexes (oxalate, phytate, cellulose) and enhanced by soluble (vit C, AAs and pectins)
What is transferrin? Blood plasma protein the binds iron very tightly. Regulates iron absorption. Transferrin saturation = iron - transferrin/total transferrin
What are the mechanisms of iron absorption? Fe3+ is converted to Fe2+ by vit C in the SI lumen then transported into the mucosa. Heme iron is also transported in and then hydrolyzed. Form Fe pool that transports Fe out to plasma-binds to transferrin in Fe3+ form or stored bound to Ferritin.
What are the functions of iron? oxygen transport in RBC - hemoglobin & myoglobin. Redox active component of cytochromes (heme) and iron sulfur centres (non heme). iron metalloenzymes (non heme).
What are the symptoms of iron deficiency? anemia. poor capacity for physical work and impaired cognitive development related to oxygen transport and metabolism of neurotransmitters.
What are the mechanisms of iron transport? Transferrin is needed to transport from intestine through blood stream. Ceruloplasmin (Cu metalloenzyme) helps bind the two by oxidizing Fe2+->Fe3+. Reliant on transferrin saturation. If saturated, excess Fe is stored in mucosal cell.
How does vitamin B6 play a role in anemia? The iron molecules in cytochromes, myoglobin and hemoglobin in heme require porphyrin synthesis. This starts with glycine and requires B6
What are the mechanisms for copper absorption? It is absorbed at 50% from luminal side and reduced in lumen. Transported in plasma by albumin and AAs to liver where it is incorporated into ceruloplasmin.
Where is excess Cu stored? In the mucosal cells. High Cu absorption is impaired by Zn. induces thionein to bind to Cu (Cu-metallothionein).
What are the sources for Cu? Shellfish, organ meats, nuts, seeds, legumes
What affects Cu absorption? enhanced by histidine, sulfur containing AAs, organic acids -lactic, citric, acetic. Inhibited by phylate, zinc.
What are the functions of Cu? Fe metabolism, electron transport (cytochrome C oxidase), oxygen radical metabolism, elastin formation, melanin formation from tyrosine
What does Cu deficiency cause? anemia (related to Fe transport), hemorrhaging (poor elastin in arteries - aortic rupture), depigmentation of skin (tyrosinase is a Cu enzyme required to make melanin)
What is hemolytic anemia? it is the breakdown of RBC due to a shortage of vit E, selenium or cysteine. Weak due to lack of antioxidants, attacked by free oxygen radicals.
What is megaloblastic anemia? deficiency of folate or B12 affects DNA synthesis and produces immature, enlarged RBCs. RBC count is low.
What is microcytic anemia? Small, hypochromic RBCs. Deficient B6 causes shortage of porphyrin for Fe to bind. Deficient Fe causes shortage of hemoglobin. Deficient Cu causes shortage of ceruloplasmin - Fe lost in feces.
What are the functions of zinc? contains <200 known enzymes, involved in all pathways of metabolism, oxygen radical metabolism, zinc fingers & DNA binding, induce metallothionein in mucosa cells - binds Cu
What are the sources for zinc? normally complexed with peptides/proteins, nucleic acids. in red meats, organ meats, whole grains, leafy vegetables.
What are the symptoms of zinc deficiency? poor growth, skin lesions, impaired sexual development in boys (required for testosterone synth).
What are "zinc fingers"? loops of DNA-binding AAs which are held in the right position by the binding of a zinc ion. Zn binds to histidine and cysteine side chains
How is dietary protein metabolized? digested as AAs. broken down into structural, regulatory and transport proteins. AAs catabolized into alphaKG (glucose and acteyl CoA for energy) and NH3/NH4+.
What are the basic AAs? lysine, arginin and histidine
What are the acidic AAs and their neutral amides? Asparate (asparagine) and glutamate (glutamine)
What are the neutral AAs - aliphatic, straight? glycine, arginine
What are the neutral AAs - aliphatic, branched? leucine, isoleucine, valine
What are the neutral AAs - aliphatic, hydroxylated? serine, threonine - tyrosine is also hydroxylated but is an aromatic
What are the neutral AAs - aliphatic, SAA? cysteine, methionine
What are the neutral AAs - aromatics? phenylalanine, tyrosine, tryptophan
What is the neutral AAs - imino? proline
What are the essential amino acids? lysine, leucine, isoleucine, valine, methionine, phenylalanine, threonine, tryptophan, histidine, arginine, glycine. Human adults do not require His, Arg, Gly and babies & rats do not need Gly. Chicks need all.
Where do complete proteins come from? Animal sources - meat, dairy, eggs. Exception is soybeans.
What are some incomplete proteins? Legumes (SAA), vegetables, cereal, grains (lysine).
What is the protein efficiency ratio? young rats fed a diet deficient in protein (10% DM) over four weeks, rats weighed at beginning and end, growth is measured (weakness). total body weight gain/test protein consumed (weighed in grams)
What is a chemical score? hydrolyze protein to free AAs and quantify by HPLC. compare to composition of whole egg. limiting AA determines score. (limiting AA/amount of same AA in whole egg)x100. weakness - doesn't account for digestibility
What is nitrogen balance? NB = N intake - N loss (urine, feces). growth, NB positive; adults, ~0; old age, NB negative. Marginal protein quality reduces NB.
What are the risks in taking in too much protein? cancer, CVD (too much animal protein), aggravates kidney disease
What are the causes and symptoms of Kwashiorkor? Adequate calories deficient in protein leads to edema (altered heart function with decreased plasma proteins). eventually leads to immune depression. high mortality rate.
What are the causes and symptoms of Marasmus? Diet deficient in energy and protein (balanced diet but not enough). complete loss of body fat. infants developing marasmus can shift to Kwash. due to stress. leads to immune depression.
What are the mechanisms of protein digestion in the stomach? homogenized protein transported to stomach, HCl denatures. pepsinogen excreted by chief cells and unfolds to pepsin. pepsin cleaves pepsinogen to create more. parapepsinogen 1&2 unfold to parapesin. act on protein to make oligopeptides. go to SI.
How is the pancreas involved in protein digestion? SI releases CCK to pancreas. initiates release of: pancreatic juice, bicarbonate, trypsinogen, chymotrypsinogen, proelastase, procarboxypeptidases to SI
What happens to the zymogens released by the pancreas? enterokinase is secreted within SI and activates trypsinogen to trypsin. trypsin acts on other zymogens to create more trypsin, chymotrypsin, carboxypeptidease A&B and elastase. aminopeptidase is also secreted from SI
What do the endopeptidases do in protein digestion? attack oligopeptides to make free AAs and small peptides. attack proteases on peptide chains to cleave AAs.
Where does trypsin attack on a peptide chain? lysine and arginine
Where does chymotrypsin attack on a peptide chain? aromatics, methionine, asparagine, histidine
Where does elastase attack on a polypeptide? on neutral aliphatics, polypeptides to oligopeptides and tripeptides.
Where does aminopeptidase attack a polypeptide? It is an exopeptidase and it attacks at the N terminal. Carboxypeptidases attack at C terminal- A cleaves aromatic neutrals or neutral AAs, B cleaves basic AAs
What does active transport require? Na-dependent, requires ATP
Where do the protein fragments go after being cleaved in the small intestine? to the liver through the portal vein where free AAs synthesized into liver enzymes, liver proteins, albumin (+other transport proteins), peptide hormones. BCAA go to systemic circ. excess AA degraded, NH3 to urea cycle, alpha keto acids to energy stores.
Where does the urea end up in the nitrogen cycle? Processed in liver. Can go to kidneys for excretion, to parotid for salivary secretion or back to the rumen
What is the function of the stomach? Mechanical mixing, HCl secretion (protein denaturation of hydrogen and electrostatic bonds), enzymatic digestion
What is the role of the small intestine? Absorption. 2x10^23 AA per meal. Digestion yields peptides and free AAs
What are the mechanisms for absorption in the small intestine? peptides and H+ are transported across the BBM. H+ is pumped out and N+ is pumped in across BBM at the same time that Na+ is pumped out and K+ is pumped in at BLM, to maintain gradient.
Why is non protein nitrogen used? Urea can be broken down by bacteria to release 2 NH3 and they can use it to make more AAs. Protein turnover in other tissues will release N as urea to go to rumen as well.
What are the three fates of nitrogen in the ruminant nitrogen cycle? AA catabolized by bacteria producing NH3 which diffuses out to circulation and made into urea in liver. Can be excreted by kidneys or move from blood stream into saliva-> rumen or diffuses into rumen from portal blood stream.
Created by: mizzlarabee on 2008-11-26



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