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Shape of a polypeptide chain

  1. Jun 18, 2004 #1
    how does the diff in shape of a polypeptide chain( alpha helix or beta pleated sheet) give rise to a diff in properties and functions?
    thanks for yr ans...
  2. jcsd
  3. Jun 18, 2004 #2
    Are you studing for exams or something?

    Different shape IS different properties. Eg, alpha helix, used especially in the formation of fibres like collegen. Beta sheets .. umm.. can't think of anythign.

    Actually, this pops into mind concerning prions. The difference between PrPc (wildtype) and PrPsc (malformed) is not related in differnces in sequence, rather than form. I think PrPc is mainly composed of alpha-helixs while PrPsc, these have been turned into beta-sheets which is resistant to proteases- and thus causes the accumulation of plaques and a diseased state.

    Again, i hope i'm right..
  4. Jun 18, 2004 #3


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    Beta sheets are usually found in transmembrane proteins such as porins.

    The structure will determine were some amino acid will be. Hydrophobic a.a. will be at the more center of the protein. Alpha helix tend to introduce rigidity and rodlike structure. Beta sheet gives high tensile strength. There is also Random Coil in which the amino acid chain takes up an irregular configuration with no tendency to form alpha helices for beta strands. Segment of random coil are as significant to protein structure as the more regular conformations because they provide opportunities for the amino acid chain to bend back on itself, thereby allowing proteins that contain alpha-helical or beta-strand segment to fold into compact, globular forms.

    the secondary will expose certain amino site in a given position. These expose a.a. will interact with other a.a. and form certain bounds. These bounds will enable certains properites such as bindings to protein or compounds.
  5. Jun 18, 2004 #4


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    Hey, why not go out look for other links, you must try to prove that you know better than iansmith, do it please.... I support you, Jikx
  6. Jun 19, 2004 #5


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    Trying to stir up some competition? :biggrin: but iansmith did a good job explaining, it is rigity and access to hydrophobic groups that will determine subsequent folding of a protein.
  7. Jun 19, 2004 #6


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    A little off-topical though, since it tells people that I am an "apparent" pot-stirrer, it can never be bad of me to say something like that, right ?
    I also doubt about some similarities of the two, but I amnot really sure, Zenbu O makase itashi tai to omotte orimasu. Go zon ji deshi ta ka ? O negai itashimasu !
  8. Jun 19, 2004 #7
    thanks guys...u r rite...i m studying 4 some tests....i hate mid term tests....
  9. Jun 19, 2004 #8


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    Where are you living ? Do US schools have mid-term tests in July ?
    Last edited: Jun 19, 2004
  10. Jun 19, 2004 #9
    There is no comparison between the knowledge tank that is iansmith, and the guy who set fire to the bottle of ethanol after dipping in the redhot metal-loop during microbiology lab (i.e me).

    Lucky Evil, only mid-term... i have my end of semester biochem exam this thursday.
  11. Jun 24, 2004 #10
    mine is next week...
  12. Jun 24, 2004 #11


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    NEC, plenty of universities offer classes in the summer. A lot of people will take a hard course like biochem over the summer because they can focus on just that one class, others will take an easy class that's outside their major to get some required coursework out of the way (I used to do that for my lit classes since I'd spend my summers reading books anyway, so figured I might as well let someone else pick the books and get credit for it).

    Evil, good luck on your midterms. And Jikx, hope your final went well today.

    Iansmith gave a pretty succinct answer. The most important part is in the second of his two paragraphs, that these different conformations expose different amino acids to allow the molecule to have its specific properties. For example, in the linear structure, two amino acids might be very far apart, but because of the folding of the molecule, those amino acids may wind up adjacent to one another and allow the molecule to bind something else (for example, those amino acids might be critical to forming the binding site in a receptor).
  13. Jul 1, 2004 #12
    thanks for the luck.
  14. Jul 1, 2004 #13
    Man.. My college sucks. It only offers the freshmen intro biologies over the summer, and the nursing student A&P classes.. That's it! We only have one micro class (an intro) during normal semesters. We have a physiology class offered once a year, and a histology offered once a year. That's like the only medical or human-biology classes we have. Well, we also have genetics.

    Grr.. ;) I see other peoples colleges that have like immunology, and all kind of great biologies... I'm so jealous, but its too late to trasnfer.
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