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My misunderstandings about protein structure

  1. Oct 27, 2009 #1
    Ok as the title suggests I want to clear up my misunderstandings on protein structure.

    1. When they say primary,secondary,tertiary and quarternary structure do they mean different stages of a protein. What I mean is do all proteins have a tertiary or quarternary structure and are primary,secondary structures simply stages of them before they became a protein. Or do some proteins remain in secondary or primary structure.
    2. "Myoglobin is a single-chain globular protein of 153 amino acids, containing a heme (iron-containing porphyrin) prosthetic group in the center around which the remaining apoprotein folds. It has eight alpha helices and a hydrophobic core. "(wikipedia)

    Does myoglobin have 8 different polypeptide helix chains joined or is it the same chain twisted to make 8 helixes. I thought one chain could only make one helix.

    "Collagen contains three different polypeptide helixes joined together"

    Does this make Collagen a quarternary structure. What is the basic difference between quaternary and tertiary structure. My understanding is that tertiary structure only has one chain twisted many ways and quaternary structure has two or more different polypeptide chains. Is this wrong?

    Thanks a lot for taking your time to read this. If you could help me with these basics I would be very greatful. Thank you
     
  2. jcsd
  3. Oct 27, 2009 #2

    Ygggdrasil

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    Yes, they refer to different stages of different levels of protein structure. A good analogy is a book. You can think of a writing as having different levels of structure. At the base, there are letters (amino acids) which can be strung together into words (primary structure). These words can be of different types (secondary structure) and precise arrangments of words creates sentences (tertiary structure). You can group sentences together to make paragraphs (quaternary structure).

    Now, there are proteins that lack some of these levels of structure. For example, myoglobin functions as a monomer so it lacks quaternary structure. But, myoglobin does have a tertiary structure (it's overall shape) that is formed from various helices (its secondary structural elements). I should mention, however, that there are some proteins known as intrinsically disordered proteins that lack any appreciable secondary or tertiary structure.

    Myoglobin consists of a single polypeptide chain. Different regions of this chain can form separate helices (or other secondary structural elements). The specific arrangement of the helices and the amino acid chains that link these helices form the tertiary structure of myoglobin.

    That is correct. A protein will have quaternary structure if it consists two or more separate polypeptide chains.
     
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