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Alpha and Beta linkages
Sarah_5660
#1 Posted : Tuesday, July 07, 2020 11:34:15 PM
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Hi, I'm having a tough time wrapping my head around what exactly alpha and beta linkages are and what the differences are between them. Any help or resources would be greatly appreciated!

Thanks
INSTR_Katerina_102
#2 Posted : Wednesday, July 08, 2020 12:22:28 AM
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Hi,

No problem, sugar linkages can be tricky at first to think about with all those definitions swimming around.

I have drawn a picture to try to help here. I have done one example and left the other for practice (my writing looks like a 1st grader's because I do not have a tablet)

https://ibb.co/LZqWdWs

I'll reiterate here:

1.For sugar linkages, you will name them alpha/beta based off of the anomeric carbon participating in the glycosidic linkage. For maltose, because the sugar is trans to the CH2OH, this means the maltose likage is alpha.

2.The numbers are then denoted by the carbons participating in the glycosidic bond. Often, people find the order confusing, so to clear it up: The first number is for the sugar that has the anomeric carbon in the glycosidic linkage.

The first number is almost always 1 as it is defined by the anomeric carbon. Recall that you number a chain giving the anomeric carbon the lowest possible number as it is the highest priority group. For aldoses, this means that the anomeric carbon will be one.

The second number is the carbon number C in the second sugar that is participating in the glycosidic bond. For maltose, it is 4.

I hope this helps, you can try the second example and I can post a second picture where you can check your work!
Sarah_5660
#3 Posted : Wednesday, July 08, 2020 3:50:24 AM
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So a trans linkage is alpha and a cis linkage is beta? If this is true, that would make things much simpler than I'm making them right now
Sarah_5660
#4 Posted : Wednesday, July 08, 2020 3:52:51 AM
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Sorry to double post - is the second bond a B 1-4 linkage?
INSTR_Katerina_102
#5 Posted : Wednesday, July 08, 2020 1:52:59 PM
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"So a trans linkage is alpha and a cis linkage is beta? If this is true, that would make things much simpler than I'm making them right now."

Yeah, you can just assign alpha and beta linkages using the alpha beta anomeric carbon in the bond - if it is alpha the linkage is alpha, and beta the linkage is beta.

And yep, cellulose has B(1,4) linkages :)
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