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Thread: How do you code for iron in hemoglobin

  1. #1
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    How do you code for iron in hemoglobin

    My background is astronomy, not genetics, so I'm looking for a simple answer that does not require a course in genetics.
    Hemoglobin is a protein which contains an iron atom. Proteins are coded by 64 codons which code for 20 amino acids plus a punctuation. None of the amino acids contains iron.
    How to you code for iron in hemoglobin?
    SHARKS (crossed out) MONGEESE (sic) WITH FRICKIN' LASER BEAMS ATTACHED TO THEIR HEADS

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    Haemoglobin isn't just a protein. The globin part is an assembly of four proteins, but the iron is bound to a non-protein molecule, heme, which contains a porphyrin ring with a central metal binding site consisting of four nitrogen atoms. The heme is assembled in a series of enzymatic steps, iron is added by an enzyme called ferrochelatase, and the hemes are finally bound to the globins by another enzyme.

    Grant Hutchison

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    There was an article, maybe scientific American, about haemoglobin. Extraordinary molecule, it has to both capture and release an Oxygen atom which is quite a trick. It’s a large molecule to transport just one atom. If I recall, but a fascinating evolutionary story, considering how animal life depends on it. The transport could not be done with “normal” oxygen chemistry because oxides are so stable. How many aeons did it take to evolve the molecule to allow large animals?
    sicut vis videre esto
    When we realize that patterns don't exist in the universe, they are a template that we hold to the universe to make sense of it, it all makes a lot more sense.
    Originally Posted by Ken G

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    It's a very clever molecule. The oxygen dissociation curve is sigmoid in shape, because binding of an oxygen molecule to one of the four subunit facilitates binding to the others. So it loads and unloads oxygen very effectively, and the sigmoid shape is tailored specifically to the oxygen cascade between lungs and tissues. Foetuses have different haemoglobin, with a different dissociation curve, which is tailored to the different oxygen cascade between the placenta and their tissues.
    It also binds carbon dioxide and buffers hydrogen ions, producing a couple of other useful effects. In the Haldane effect, the binding of oxygen reduces the affinity for carbon dioxide--so deoxyhaemoglobin passing through the tissues picks up CO2, but then releases it in the lungs as it picks up oxygen. In the Bohr effect, increases in carbon dioxide and hydrogen ion concentration decrease haemoglobin's affinity for oxygen. So when oxyhaemoglobin arrives in a part of the body with a high metabolic rate (producing carbon dioxide and other acids), it dumps more oxygen than it would otherwise do.
    All mediated by conformal changes and shifts in polarity.

    Grant Hutchison

  5. #5
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    Quote Originally Posted by grant hutchison View Post
    It's a very clever molecule. The oxygen dissociation curve is sigmoid in shape, because binding of an oxygen molecule to one of the four subunit facilitates binding to the others. So it loads and unloads oxygen very effectively, and the sigmoid shape is tailored specifically to the oxygen cascade between lungs and tissues. Foetuses have different haemoglobin, with a different dissociation curve, which is tailored to the different oxygen cascade between the placenta and their tissues.
    It also binds carbon dioxide and buffers hydrogen ions, producing a couple of other useful effects. In the Haldane effect, the binding of oxygen reduces the affinity for carbon dioxide--so deoxyhaemoglobin passing through the tissues picks up CO2, but then releases it in the lungs as it picks up oxygen. In the Bohr effect, increases in carbon dioxide and hydrogen ion concentration decrease haemoglobin's affinity for oxygen. So when oxyhaemoglobin arrives in a part of the body with a high metabolic rate (producing carbon dioxide and other acids), it dumps more oxygen than it would otherwise do.
    All mediated by conformal changes and shifts in polarity.

    Grant Hutchison
    Does that mean a baby makes a quick change upon birth and suddenly becoming an air breather?

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    Quote Originally Posted by Hornblower View Post
    Does that mean a baby makes a quick change upon birth and suddenly becoming an air breather?
    Not instantaneous, but the transition begins in a slow way before birth and then takes off during the first three months after birth. Adult haemoglobin (HbA) is made up of alpha and beta globin chains; fetal haemoglobin (HbF) from alpha and gamma. So the switch-over involves suppressing one set of genes and activating another. There are various things that can go wrong with that, producing disease states. Much more here.

    Grant Hutchison

  7. #7
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    I don't see that anyone's linked to a pic of heme yet. Here it is: https://en.m.wikipedia.org/wiki/Heme
    Chlorophyll in plants is very similar, except that it binds magnesium rather than iron: https://en.m.wikipedia.org/wiki/Chlorophyll

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    What about those deep sea animals that use copper instead of iron, IIRC? What does their protein look like?
    SHARKS (crossed out) MONGEESE (sic) WITH FRICKIN' LASER BEAMS ATTACHED TO THEIR HEADS

  9. #9
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    Haemocyanins aren't unique to deep sea animals--they're widely distributed in molluscs and arthropods. The geometry varies from species to species, but the copper binding site is formed from the arrangement of several residues of the amino acid histidine. So instead of a "nest" of pyrrole nitrogens (as you have in heme) you have a group of imidazole nitrogens.
    The genetic coding in this case is for an amino acid sequence that will naturally fold (search on "protein tertiary structure") into a copper binding site with several histidines all facing in the right direction and with the right separation. I'd guess an enzyme is then involved in placing the copper, but I don't know.
    Histidine often turns up in these roles where proteins bind to other things. Its imidazole nitrogen seems to be quite versatile in that regard.

    Grant Hutchison

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