Which of the following statements is/are true concerning peptide bonds? they are the only covalent bond formed between amino acids in polypeptide structures. the angles between the participating c and n atoms are described by the values psi (psi) and phi (phi). they have partial double-bond character. all of the above.

All of the above are true.

A peptide bond is an amide type of covalent chemical bond. It is formed between two amino acids:  C1 (carbon end) of one alpha-amino acid and N2 (nitrogen end) of another. Peptide bonds are the basis for the formation of a peptide chain and consequently protein.  Formation of peptide bond is a condensation process, meaning that when two amino acids combine and link, water molecule is released and dipeptide is a product of that reaction.

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the correct answer is:

a population changes in response to a change in the environment.