How many possible four aminoacid long peptides (a peptide is a small protein)?

Question

can be made from the below peptides.
(I.E. rearrange them to form different sequences, where each sequence is made up of only the four aminoacids given below)



asp met asp met

Answer 1

Is this what you mean?

asp asp met met
asp met asp met
asp met met asp
met met asp asp
met asp met asp
met asp asp met

I get six.


Edited to note: amino acid molecules are different on each side of the "R" group, meaning that even if the amino acid sequence is a mirror image of another sequence, the peptide molecule will be different if it's read forward versus backward. So there are still six, not four combinations.

Answer 2

8

Answer 3

some of Dana's combinations are redundant (forwards or backwards doesn't matter with a small peptide like this).

asp asp met met (met met asp asp -- is the same)
asp met asp met (met asp met asp -- is the same)
asp met met asp
met asp asp met

So, I get 4

Answer 4

20 x 20 x 20 x 20 (assuming 20 possible amino acids allowing for repeats)