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Tyrosine derived hormones

Discussion in 'MCAT Discussions' started by byronicbear, Feb 24, 2012.

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  1. byronicbear


    Mar 17, 2008
    SDN 2+ Year Member

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    Hi all,

    I am a bit confused about Tyrosine. I though tyrosine has a polar side chain so it's a polar molecule. However, tyrosine is lipid soluble!:confused:

    Could someone help me out here?
    Many thanks in advance.
  2. tetrahedral22


    Jul 3, 2011
    Hello byronicbear,

    Tyrosine-derived amine hormones are divided into two major classes: catecholamines and thyroid hormones. It's important to know this because one class behaves like peptides and the other like steroids.

    Catecholamines (epinephrine and norepinephrine) are produced in the adrenal medulla and act like peptide hormones, i.e. act on cell membranes in order to activate second messenger G proteins through adrenergic receptors. They are minimally-modified tyrosine monoamines (with an extra hydroxyl on the tyrosine side-chain ring, increasing its polarity) so they do not cross the cell membrane.

    Thyroid hormones (T4, T3) are more processed and include two iodinated benzyl rings, making the molecules sufficiently non-polar that they can easily diffuse through the cell membrane and act on nuclear receptors to cause metabolic changes (like steroid hormones). Think of them as being more steroid-like because of the extra ring.

    I hope this helps!
  3. SN2ed

    SN2ed Moderator

    Jun 27, 2007
    Resident [Any Field]
    SDN 7+ Year Member
    Thread closed. These types of questions belong in the MCAT Study Q&A forum.
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