NFS 4271 Study Guide - Quiz Guide: Selenate, Heavy Metals, Sulfite Oxidase

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17 Sep 2017
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Chapter 13: Essential Trace and Ultratrace Minerals
Reading Assignments
Chapter 13: Essential Trace and Utratrace Minerals from Advanced Nutrition and Human
Metabolism
As you read chapter 13 from Advanced Human Nutrition and Metabolism, focus on the following:
1. Explain the difference between trace and ultratrace minerals
Iron
Define the following terms:
Ferric iron (Fe 3+) - most nonheme form found in most foods
Ferrous iron (Fe 2+) - most supplements are in this form
Heme iron: iron that is contained within the porphyrin ring structure; derived mainly from
hemoglobin and myoglobin and thus is found only in animal products; about 50-60% of the
iron in meat, fish, and poultry is heme
Non-heme iron: the rest of iron is found as nonheme iron found primarily in plant foods
(nuts, fruits, vegetables, grains, tofu) and dairy products (milk, cheese) and eggs, although
dairy products contain very little iron and represent a poor source of iron
Metalloporphyrin: heme iron
Porphyrin: A class of pigments (including heme and chlorophyll) whose molecules contain a flat
ring of four linked heterocyclic groups, sometimes with a central metal atommg or fe
Ferrous sulfate: inexpensive, causes GI problems
65 mg iron per serving given to treat iron deficiency
Ferrous gluconate: lower risk of GI intolerance, low amounts of elemental iron
27 mg iron per serving, very inexpensive
Ferrous fumarate: expensive, highest proportion of elemental iron
106 mg elemental iron
Fewer tablets per bottle
Gentle on the stomach
High potency
Iron Dextrans
Chelated iron: small organic complexes made with iron ions.
Outline the digestion and absorption of heme iron and of non-heme iron. Include the roles of DMT
1, hepcidin, ferroportin
Iron is released from bound food components. Some HCl in the stomach may reduce Fe 3+
to Fe 2+
Free heme is absorbed intact by heme carrier protein (hcp) 1, located primarily in the
proximal small intestine (throughout all the small intestine, but most efficient in the
proximal portion of the duodenum).
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Heme iron must be hydrolyzed from the globin portion of hemoglobin and
myoglobin (accomplished by proteases in the stomach and small intestine and
results in the release of heme from the globin
Proton-coupled folate transporter (PCFT) has also been identified as a heme carrier
Within the enterocyte, heme porphyrin ring is catabolized by heme oxygenase to
protoporphyrin and Fe 2+
Released iron is stored as ferritin
Nonheme iron in the small intestine may react with one or more inhibitors, which promote
the fecal excretion of iron; must be hydrolyzed in the GI tract, aided by HCl and proteases
Any of three reductases, cytochrome b reductase 1, cytochrome b (558) ferric cupric
reductase, and six trans-membrane epithelial antigen of the prostate (steap) 2, may reduce
Fe 3+ to Fe 2+
In the brush border, divalent metal transporter (DMT) 1 carries Fe 2+ across the brush
border membrane into the cytosol of the enterocyte, although endocytosis of DMT1 as part
of transcytosis may also enable iron absorption
Fe 2+ may bind to poly rC binding protein or a yet unidentified protein for transport in the
cytosol; iron may also be used within the cell or stored part of ferritin.
Ferroportin transports iron across the basolateral membrane. Iron transport is coupled
with its oxidation to Fe 3+ by hephaestin
Fe 3+ attaches to transferrin for transport in the blood.
Describe factors that enhance and interfere with iron absorption. As related to non-heme iron
absorption, what is meant by  units of vitamin C or MFP and what effect do they have on iron
absorption? Explain what mucin, pholyphonols, and phosvitin are and how they affect iron status.
Enhancers of iron absorption:
Decreased iron stores
Increased erythropoietic activity (when we’re making more blood)
Anemia (low iron)
Hypoxia (low oxygen) --> iron carries oxygen
Sugars (fructose, sorbitol), acids (ascorbic, citric, lactic, tartaric), acidic pH, mucin,
meat, fish, poultry factors (MFP)
mucin: an endogenously synthesized chelator, is a small protein made in both
gastric and intestinal cells; binds multiple ferric iron atoms at an acid pH and
maintains ferric iron solubility in the alkaline pH of the small intestine to
enhance iron absorption.
Inhibitors:
Alkaline pH, polyphenols, oxalic acid (tea), phytic acid/phytates (whole grains),
Phosvitin (found in egg yolks), divalent cations ( Ca, Zn, Mn)
The amount of iron available for absorption can be estimated from the quantity of vitamin
C and MFP that is ingested with the nonheme iron. 75 units of ascorbic acid or MFP (=1.3 g
raw or 1 g cooked MFP, or 1 mg ascorbic acid) has been shown to maximize iron absorption
when consumed with the iron source. Units of 75 seem to have no further benefits.
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Mucin:small protein made in the gastric and intestinal cells; binds multiple ferric iron
atoms at an acid pH and maintains ferric iron solubility in the alkaline pH of the small
intestine to enhance iron absorption
Polyphenols: such as tannin, when consumed with a source of nonheme iron, can reduce
iron absorption by over 50%
Coffee consumption, with or just after a meal, may reduce iron absorption by 40%
Phosvitin: a protein containing phosphorylated serine residues found in egg yolks, inhibit
nonheme iron absorption
Explain how iron is transported, taken into cells, and how and where the mineral is stored. (Define
ferritin, transferrin, and hemosiderin.)
Ferric iron is bound to transferrin; together it attaches to transferrin receptors on cell
membranes.
Transferrin: a glycoprotein made in the liver, binds iron (protective mechanism);
ferries iron throughout the body; delivering both new and recycled iron to tissues.
(transferrin has a half-life of about 7 to 10 days)
After attachment, the complex is endocytosed into the cell cytosol where it forms an
endosome.
A drop in pH in the endosome helps initiate the release of ferric Fe 3+, which is then
reduced by steap3 and transported out of the endosome by a transporter such as DMT1
into a ferrous state.
Protons are pumped into endosome to drop pH from 7.4 to 5.5.
Fe 2+ released from the endosome may be oxidized and stored as part of ferritin.
Fe 2+ may be used within the cell functionally.
Ferritin is the primary storage form of iron in cells; the role of iron in the control of ferritin
synthesis: less ferritin is made in cells when cellular iron content is low.
IRE: iron regulatory element
IRP: iron response proteins
In low-iron: IRE-BP binds to an IRE in the ’ untranslated region of ferritin mRNA
and acts as a receptor to inhibit the translation of the ferritin protein
Hemosiderin is another iron storage protein.
Outline the various functions of iron.
O2 transport and use
Amino acid metabolism
Antioxidant
Carnitine
Collagen
Thyroid hormone synthesis
What is meant by iron turnover and how is it accomplished?
avid conservation and constant recycling og body iron to ensure adequate supplies.
most iron entering the plasma for distribution or redistribution by transferrin results from
hemoglobin, ferritin, and hemosiderin.
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