Flashcards in Iron and heme Deck (45)
small RBCs is a clue for what type of iron dysfunction?
what is the mechanism of the Fenton reaction?
1. oxygen picks up electron from iron or copper
2. iron / copper oxidized
3. superoxide anion or hydroxyl radical produced
what are the active forms of iron?
Hb, Mb, cytochromes
iron is transported by what protein?
what is the inactive form of iron?
what is the degenerated, long term storage of iron?
what cells are the gatekeepers of iron uptake?
what is the role of divalent methyl transporter (DMT)?
uptake of iron 2+
what is the role of cytochrome B on the enterocyte?
reduces Fe 3+ to 2+ for uptake
inside the cell, iron is protected by what protein?
what is the role of ferroportin?
determines how much iron will be released from enterocyte into circulation
what is the role of hepcidin?
downregulates activity of ferroportin - blocks uptake of iron
what is the role of hephaestin?
oxidizes iron 2+ to 3+ to be taken up by ferritin in the circulation
iron is taken up into other cells by what mechanism?
the presence of hemosiderin indicates what condition?
in a hemolytic disorder involving destruction of RBCs inside macrophages, what happens to the ferritin?
accumulates then degrades to hemosiderin
what is the main regulator of iron uptake?
how does low hepcidin affect iron uptake?
a defect in what enzyme results in hereditary hemochramotosis? how?
1. human hemochromatosis protein (HFE)
2. low hepcidin production
regulation of intracellular iron storage occurs at what level?
what is the role of iron response elements (IREs)?
forms hairpin loop on mRNA for ferritin that prohibits the placement of the ribosome at the start codon (prohibiting transcription of iron binding factors)
what is the role of aconitase?
iron regulatory protein that is bound to the IRE in low iron conditions (do not need ferritin when there is already low iron)
what is the result of free iron on the IREs?
1. binds aconitase and removes it from the IRE
2. translation of ferritin can begin
where are IREs found?
1. ferritin RNA
2. ALA synthase RNA
3. transferrin receptor RNA
what is the key enzyme for heme synthesis?
what is the function of the IRE on the transferrin receptor?
repression of translation (if cell is already full of iron then you want to shut down receptors so you are not taking up more)
what does total iron binding capacity (TIBC) measure?
how does a high TIBC level relate to iron stores?
high TIBC = low iron stores
what does transferrin saturation measure?
how does a high transferrin saturation relate to iron stores?
high saturation = high iron stores
what is the best measure of iron body stores?
what is protoporphyrin?
iron-free precursor of heme
what does a high protoporphyrin level indicate?
low iron stores (not enough to load all the heme)
iron deficiency can develop into anemia via what mechanisms?
1. iron depletion
2. deficient erythropoiesis
3. low Hb (hypochromia, microcytosis)
iron overload is characterized by what findings?
1. high transferrin saturation
2. hemosiderin deposits
heme synthesis starts with what compounds?
succinyl CoA and glycine
which compound in heme synthesis is photoactive?
heme synthesis disorders
what is the precursor to UPG3? is it photoactive?
acute intermittent porphyria is a build up of what heme precursor? is it a photoactive disorder?
how does AIP affect the urine? blood?
1. dark red urine (accumulation of PBG and ALA)
2. anemia (cannot make enough heme)
porphyria cutanea tarda is a build up of what heme precursor? is it a photoactive disorder?
lead poisoning affects what steps of heme synthesis?
1. PBG synthase (ALA to porphobilinogen)
which porphyria is exacerbated by alcohol consumption (stress)?
AIP (acute intermittent porphyria)