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November 01, 2025, 12:21:06 pm
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Author Topic: A bit of help  (Read 1076 times)  Share 

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sam0001

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A bit of help
« on: May 18, 2012, 09:46:14 pm »
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Prolyl, leucyl, glycinamide. How many different tripeptides could be formed using the three amino acids?
« Last Edit: May 18, 2012, 09:49:39 pm by sam0001 »
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Mao

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Re: A bit of help
« Reply #1 on: May 18, 2012, 10:20:13 pm »
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6. PLG, PGL, LPG, LGP, GLP, GPL.
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jadams

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Re: A bit of help
« Reply #2 on: May 18, 2012, 10:45:16 pm »
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For finding the number of different combinations for a polypeptide chain, use factorials.
ie for finding the number of unique combinations for a chain of 5 amino acids:

the answer would be 5!
which is equal to 5x4x3x2x1   
= 120 unique chain combinations!
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AllAboutTheLGs

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Re: A bit of help
« Reply #3 on: May 18, 2012, 11:59:58 pm »
+1
Yeah factorials are a really good way to remember them. Just be careful if there are 2 of the same amino acid though
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pi

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Re: A bit of help
« Reply #4 on: May 19, 2012, 12:14:05 am »
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Just on the side for those who may become confused, this method will NOT work for finding the number of isomers of a particular molecular formula (especially in relation to alkanes).

A good tip (this is getting random lol) for alkanes (non-cyclic) is that if you half the number of Cs in the alkane and round up, that is the number of possible isomers :)
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charmanderp

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Re: A bit of help
« Reply #5 on: May 19, 2012, 01:45:02 pm »
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When given a molecular formula I always just try to draw as many different structural isomers as possible, and then name them all to make sure that I haven't doubled up.
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