lecture 20: iron

Question 1

factors that affect iron bioavailability

Answer 1

interactions with ligands
organic acids enhance absorption
inhibitory ligands: phytates, polyphenols, calcium, fiber

Question 2

mechanisms of iron exchange, transport, and storage must maintain…

Answer 2

an extremely low free iron concentration (can generate highly cytotoxic free radicals)

Question 3

storage forms of iron

Answer 3

ferritin and hemosiderin

Question 4

ferritin structure

Answer 4

H subunits: ferroxidase activity (Fe2+ to Fe3+), limits Fe2+ induced production of hydroxyl radicals
L subunits: nucleation of iron core of ferritin

liver and spleen (iron storage): higher proportion of L subunit
heart and brain (iron detox): H subunits predominant

Question 5

transferrin

Answer 5

transport of iron, facilitates iron uptake
synthesized in liver
two-iron binding sites, tight Fe3+ binding

Question 5

transferrin receptors

Answer 5

involved in cellular uptake of transferrin bound-iron from circulation, high affinity for Fe3+

Question 5

iron (Fe2+) export

Answer 5

occurs via ferroportin, works with ferroxidases to export iron out of the cell
dependent on transferrin and ferroportin

Question 5

transferrin-bound uptake by cells

Answer 5

mediated by expression of transferrin receptors
transferrin binds > complex is invaginated into clathrin-coated pits to form vesicles
Fe3+ reduced to Fe2+

Question 5

ferroportin

Answer 5

export of Fe2+ (ferrous iron)
works with ferroxidases to oxidize to Fe3+ before loading to apotransferrin

Question 6

DcytB

Answer 6

membrane bound, reduces Fe3+ to Fe2+

Question 7

DMT1

Answer 7

absorbs iron from GI tract after reduction to Fe2+

Question 8

uptake of luminal heme iron into enterocytes

Answer 8

heme iron more bioavailable than non-heme

after absorption, degraded by heme oxygenase resulting in free Fe2+

Question 9

erythroblasts

Answer 9

nucleated developing RBCs, eventually becomes erythrocyte (mature RBC)

takes up transferrin-bound iron and transported into mitochondria to form heme

Question 10

biological functions of iron

Answer 10

exists in several oxidation sates
transport/metabolism of oxygen
movement of electrons

Question 11

iron proteins can be classified according to the coordination chemistry of their iron

Answer 11

heme proteins, iron sulfur proteins, non heme non iron sulfur protiens

Question 12

heme proteins

Answer 12

single iron bound by heme
O2 transport, e transfer, cyt P450 metabolism

oxygen carriers hemoglobin and myoglobin
unoccupied 6th coordination site- binding site for O2, inorganic ligands, organic ligands
AA 6th site - e transfer

Question 13

6th coordinate position of heme in electron transporting cytochromes

Answer 13

6th coordinate position occupied by an AA residue
cytochromes transport electrons, alternate iron in heme between Fe3+ and 2+

Question 14

iron-sulfur cluster proteins

Answer 14

most common: 2Fe-2S and 4Fe-4S
electron transfer rxns, initiating catalysis, biological sensors

Question 15

mononucleur non-heme iron proteins

Answer 15

single Fe atom, involved in rxns with O2 as substrate
1st subgroup: aromatic AA hydroxylase
2nd subgroup: dioxygenases, requires keto acid substrate
one O2 transferred to substrate, other to keto-acid

Question 16

dinuclear non-heme iron proteins

Answer 16

dinuclear iron sites
involved in Fe2+ to Fe3+ oxidation

Question 17

iron deficiency

Answer 17

low hemoglobin conc > anemia

more anemic in underdeveloped/developing regions: less meat, more food that blocks iron absorption - PHYTATES

exacerbated by infectious diseases