Micronutrients (Essential Trace Minerals)

Question 1

What are the two forms that iron is found in food

Answer 1

1. Heme (poryphorin ring of hemoglobin and myoglobin) - in animals
2. non-heme (plants)

Question 2

Which two states of iron are stable in the aqueous environment of the body and in food?

Answer 2

Fe3+ and Fe2+

Question 3

What are the functions of iron?

Answer 3

• oxygen transport (hemoglobin/myoglobin)
• redox rxns
• iron metalloenzymes

Question 4

Is the RDA for iron higher in men or women? why?

Answer 4

women due to menses (also higher in pregnant women to cover fetus needs)

Question 5

What is the difference between how heme and non-heme iron are absorbed?

Answer 5

• non-heme: Fe3+ must be converted to Fe2+ by reductase enzyme to be absorbed by DMT1 (divalent metal transporter 1)
• heme: absorbed as-is by HCP1 (heme carrier protein 1) and then broken down by heme oxygenase in intestinal cells to release Fe2+ and protoporphyrin

Question 6

What are the three fates of Fe2+ after being absorbed?

Answer 6

1. used in intestinal cells
2. stored as ferritin in intestinal cells
3. transported into blood by ferroportin

Question 7

What are chelators?

Answer 7

• small organic compounds that form a complex with a metal ion
• can enhance absorption (if soluble)
• can inhibit absorption (if insoluble)

Question 8

How is iron transported in the blood?

Answer 8

as Fe3+ bound to transferrin carrier protein
(unbound Fe2+ is highly reactive ; can easily lose an electron and form free radicals)

Question 9

What is the difference between ferritin and hemosiderin in the storage of Fe3+?

Answer 9

• Ferritin - iron is readily available
• Hemosiderin - iron is poorly available

Question 10

How is Cu2+ absorbed and transported?

Answer 10

• Cu2+ must be released from bound amino acids by HCl and pepsin to be absorbed
• Cu2+ must be reduced to Cu+ to be absorbed
• specific transporters in small intestine
• transported to liver bound to protein where it is incorporated into ceruloplasmin

Question 11

What is Menke’s disease?

Answer 11

X-linked genetic disease (gene ATP7A) where the body cannot absorb enough copper

Question 12

What is Wilson’s disease?

Answer 12

excess copper that cannot be excreted in bile due to a mutation in ATP7B gene which causes copper to accumulate in the brain, kidneys and eyes after the liver reaches capacity

Question 13

What are the main functions of zinc?

Answer 13

• metalloenzymes that stabilize tertiary structure of a protein and play roles in reaction site of an enzyme
• oxidant defense
• DNA binding (Zn fingers)

Question 14

How is Zinc absorbed?

Answer 14

• must be released from amino acids before absorption - HCl and digestive enzymes in small intestine
• carrier mediated absorbance (ZIP4) or simple diffusion

Question 15

Is the RDA for zinc higher in men or women? Why?

Answer 15

Men, to support testosterone function