Question 1185640: In how many ways can four different amino acids be arranged into a polypeptide chain of five amino acids?
Found 2 solutions by ikleyn, greenestamps:
Answer by ikleyn(52780)   (Show Source):
You can put this solution on YOUR website! .
In how many ways can four different amino acids be arranged into a polypeptide chain of five amino acids?
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As far as I know, at this forum, no one of our tutors is biologist or molecular biologist, or biochemist, or organic chemist.
Therefore, I will not answer your question, as it is posed in the post.
I will answer another question.
In how many different ways 4 different items can be distributed in 5 different boxes
having no more than one item per box?
The answer is 5*4*3*2 = 120 different ways, by placing
item 1 in any of 5 boxes,
item 2 in any of remaining 4 boxes,
item 3 in any of remaining 3 boxes,
item 4 in any of remaining 2 boxes.
It would be interesting to me to learn it from you, if my response/solution really answers your question.
PLEASE let me know.
Answer by greenestamps(13200)  (Show Source):
You can put this solution on YOUR website!
I don't think the "similar" problem solved by the other tutor is equivalent to your problem....
The wording of the problem implies that all four different types of amino acids are used in the chain of 5 amino acids. So we are arranging the symbols AABCD.
(1) We first need to choose 1 of the 4 amino acids to be the one that occurs twice:  .
(2) Then we can arrange the 5 amino acids, of which 2 are the same, in a chain: 
ANSWER: 4*60 = 240 different strings of the four amino acids are possible if the string contains all of the four types of amino acids and two are the same.
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