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Right and left handed amino acids

  1. May 21, 2016 #1
    In nature, do right and left handed amino acids act like magnets in that right and left bind more readily than left + left or right + right?

    Do amino acids bind with each other, creating functional proteins without the help of other molecules/catalysts? At what temperatures/pressures does this process occur most efficiently?

    Or do amino acids need to be assembled into proteins using molecular machinery?
     
  2. jcsd
  3. May 21, 2016 #2
    Amino acids do not spontaneously combine to make proteins.
    The sequence of amino acids necessary to make a protein is encoded in DNA.
    These 'instructions' are transcribed as RNA, then this RNA carries the information to specialised 'organelles' (ribosomes) within a cell.
    This is where the actual protein assembly takes place.
    https://en.wikipedia.org/wiki/Protein_biosynthesis
     
  4. May 21, 2016 #3

    Ygggdrasil

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    No. Proteins are composed of only L-amino acids because the cellular machinery that makes proteins recognizes only L-amino acids. However, it is possible to synthesize peptides with a mix of D- and L-amino acids.

    Yes, two amino acids will not spontaneously react to form a peptide bond, so catalysts and other molecules are required to aid the process. Although the most practical way of making proteins is to use cellular machinery, small proteins can be synthesized in the lab without using any biological machinery, through a process called solid-phase peptide synthesis).
     
  5. May 29, 2016 #4
    If amino acids do not spontaneously form peptide bonds, how did the first proteins form in the primordial soup?
     
  6. May 29, 2016 #5
    I was wondering about that too. It seems that peptide bonds are endothermic and hydrophobic as well, so the bonding process would require an input of energy. And if there was water present it would have been even more difficult...

    How many different amino acids need to assemble in the proper order to create a protein used in a ribosome? And how would the proteins fold properly to become functional? As I understand it, protein folding is extremely inefficient in vitro.
     
  7. May 29, 2016 #6

    Ygggdrasil

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    Proteins are thought to have come somewhat later in the process of abiogenesis. Current models postulate that an RNA world preceded modern biology based on proteins, DNA and RNA. Proteins would come later after catalytic RNAs evolved the ability to catalyze peptide bond formation.

    As mentioned above, protein synthesis is thought to have originated from a set of RNA catalysts (ribozymes) that evolved the ability to activate amino acids (use energy to bind amino acids to tRNA like molecules) and catalyze peptide bond formation. The ribosome, which catalyzes protein synthesis in modern cells, is thought to be a relic from the RNA world because even though the ribosome is a complex of protein and RNA, only the RNA seems to be involved in catalyzing peptide bond formation.
     
  8. May 29, 2016 #7
    My bet would be on very simple forms of RNA appearing first, and then out of millions of random combinations, one of them happened to be similar to what now is ribosomal RNA. establishing a mechanism by which that RNA and it's derivative protein becomes a self replicating system.
    From that point on natural selection gets it's foot in the door and the system becomes not only self replicating, but self-enhancing.
    Note, this is not just personal speculation, it is a fairly well supported hypothesis.
    https://en.wikipedia.org/wiki/RNA_world
     
  9. May 29, 2016 #8
    Too late to edit the above...
    I'm not sure if the protein produced in this scenario has a big role to play, RNA can have protein-like properties just by itself.
    The protein could have been just helpful as slimy substrate that holds things together so that more of other RNA chemistry can occur.
     
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