is it that the ends of the monomers contain the SAME atoms (OH-OH) and (H2N-NH2).
Almost !
Remember, the amide link is formed from the reaction of COOH with NH
2 (or COCl with NH
2).
If we use R
1 and R
2 to denote pretty much any combination of atoms, but for simplicity sake chains or rings of CH, such as ethyl or phenyl
We have the reaction of di-carboxylic HOOC-R
1-COOH with diamine H
2N-R
2-NH
2 to form the chain. look at the structure of the chemicals in the wikipedia articles to confirm that.
I still dont know what is special about the number of functional groups, please enlighten me. But with the position, they are ends are a reflection of the other (basically the opposite way round with the same atoms)
All (pretty much all) that is important is the existence of 2 COOH on one monomer and 2 NH
2 on the other monomer - leading to the chain
... -CONH-R
2-HNCO-R
1-CONH-R
2-NHCO-R
1-CONH-...
I have written CONH and HNCO to try and show which of the C and the N in the link is bonded to either R
1 or R
2.
Can you see that? Can you see without every monomer having two functional groups you will not get chains? Can you draw it "structurally" to more clearly see the bonds between the various atoms?
Now, can you go back to the amino acids I listed (any two will do), describe what two functional groups are on every amino acid and what that means for the bonding between amino acids?