Question 1092584
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``An octapeptide is known to contain four of one amino acid, two of another and two of third. 
How many different amino acid sequence are possible?( order matters in this question)
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I will assume that ALL sequences and connections are allowed in one-line-arrangement. And, as you stated in the condition, 
the order amino acids in one-line arrangement does matter. Then the following logic works:


<pre>
    In total, there are 4 + 2 + 2 = 8 amino acid (acids ?).

    Anyone of 8 acids           can be placed in the 1-st position.
    Anyone of remained 7 acids can be placed in the 2-nd position.
    Anyone of remained 6 acids can be placed in the 3-rd position.
    Anyone of remained 5 acids can be placed in the 4-th position.

    . . . .   and so on  . . . . 

    Anyone of remained 2 acids can be placed in the 7-th position.   
    And    there is no choice (except the remained 1 last acid) in the 8-th position.

    If this logic is correct from the Chemistry/Biochemistry point of view,
    then the answer is  8*7*6*5*4*3*2*1 = 40320 different amino acid sequences are possible.
</pre>

<U>Answer</U>.  How many different amino acid sequence are possible? - 40320 different amino acid sequences are possible.


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I am not a Chemist in my education, and consider this problem from the Combinatorics point of view &nbsp;ONLY.  
So my logic easily can be wrong, &nbsp;if Biochemistry dictates other conditions.


It is your responsibility to evaluate if it is True or False.


If it not difficult to you, &nbsp;I would appreciate your feedback, &nbsp;which you can send me through the &nbsp;"Thank you" note.


In this case, &nbsp;please refer to the Problem ID number, &nbsp;which is &nbsp;1092584.


Thank you and good luck !!



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From Wikipedia,  https://en.wikipedia.org/wiki/Peptide

<pre>
    An octapeptide has eight amino acids (e.g., angiotensin II).
</pre>

From Wikipedia,  https://en.wikipedia.org/wiki/Angiotensin#Angiotensin_II

<pre>
    Angiotensin II
    Asp-Arg-Val-Tyr-Ile-His-Pro-Phe | His-Leu
</pre>

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My previous post/solution to this problem was

<A HREF=https://www.algebra.com/algebra/homework/Probability-and-statistics/Probability-and-statistics.faq.question.1091943.html>https://www.algebra.com/algebra/homework/Probability-and-statistics/Probability-and-statistics.faq.question.1091943.html</A>


https://www.algebra.com/algebra/homework/Probability-and-statistics/Probability-and-statistics.faq.question.1091943.html



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And one last notice/question/request . . . 


I got this message


&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<U>Comment from student</U>: If in this question order matters what is your answer ?



I think that this message came from you, &nbsp;although I am not &nbsp;100% &nbsp;sure.



Every day I answer &nbsp;10 - 20 - 30 posts,  &nbsp;and in &nbsp;3-4-5 &nbsp;days the number of my responses is about &nbsp;1 hundred.


Under these circumstances, &nbsp;it is difficult to me to identify to which of my posts does relate the comment from a student, 
if this comment does not refer to the problem ID. &nbsp;So, &nbsp;it is difficult to me to react adequately and timely . . . 


Therefore, . . . please do refer to the problem's ID number if you want communicate with me effectively.


Again, &nbsp;thanks and good luck !