Alpha Chains and Beta Chain polypeptides

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timthechemist
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#1
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#1
When they are referring to polypeptides, as 𝝰 and β polypeptide chains, like in hemoglobin for example, they are not meaning alpha helix and beta pleated sheet are they?

What is the difference between the 𝝰 and β polypeptide chains? or is it just nomenclature for like 1 & 2, to designate they are different?
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Lighfy
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#2
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#2
(Original post by timthechemist)
When they are referring to polypeptides, as 𝝰 and β polypeptide chains, like in hemoglobin for example, they are not meaning alpha helix and beta pleated sheet are they?

What is the difference between the 𝝰 and β polypeptide chains? or is it just nomenclature for like 1 & 2, to designate they are different?
Yes, when we say 𝝰 polypeptide, we are referring to a polypeptide chain which is in the shape of a helix. The same applies to β chains. Look at the quaternary structure of haemoglobin and notice the difference in shapes between the 4 polypeptide chains.
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Jpw1097
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#3
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#3
(Original post by timthechemist)
When they are referring to polypeptides, as 𝝰 and β polypeptide chains, like in hemoglobin for example, they are not meaning alpha helix and beta pleated sheet are they?

What is the difference between the 𝝰 and β polypeptide chains? or is it just nomenclature for like 1 & 2, to designate they are different?
Yes you are right, in haemoglobin, the alpha chains do not refer to alpha helices, and the beta chains do not refer to beta-pleated sheets. As you said, it's just the nomenclature and it just happens that there are two different polypeptides in haemoglobin, so they called one alpha and one beta. For example, foetal haemoglobin (HbF) has two alpha and two gamma polypeptide chains, but of course, there is no gamma helix/sheet (as to my knowledge). It's just a way of making. And distinguishing between different amino acids in a protein.

Hope that helps!
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timthechemist
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#4
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One of you is right and one of you is wrong. I am going with Jpw1097.

As I doubt that an entire polypeptide chain can be said to be in a-helix form the whole way. I understand that polypeptide chains have "sections" of a-helix and sections of beta sheets, as needed to make a shape, and places with neither of these two structures.
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Asklepios
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#5
(Original post by timthechemist)
One of you is right and one of you is wrong. I am going with Jpw1097.

As I doubt that an entire polypeptide chain can be said to be in a-helix form the whole way. I understand that polypeptide chains have "sections" of a-helix and sections of beta sheets, as needed to make a shape, and places with neither of these two structures.
Jpw is correct. If you do look at the structure, then you'll see both alpha and beta subunits are largely composed of alpha helices.
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timthechemist
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#6
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#6
(Original post by Asklepios)
Jpw is correct. If you do look at the structure, then you'll see both alpha and beta subunits are largely composed of alpha helices.
There you go, so the terms alpha and beta in this context have nothing to do with the terms we know in secondary structure "alpha helix" "beta sheet"

Cheers
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Asklepios
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#7
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#7
(Original post by timthechemist)
There you go, so the terms alpha and beta in this context have nothing to do with the terms we know in secondary structure "alpha helix" "beta sheet"

Cheers
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