Final answer:
Dipeptides are formed when two amino acids are linked together by a peptide bond in a dehydration synthesis reaction. The dipeptides are named using three-letter abbreviations from N-terminus to C-terminus. Therefore, all listed options a. proline-threonine, b. glycine-cysteine, c. alanine-alanine, and d. cysteine-alanine are possible dipeptides.
Step-by-step explanation:
In the context of biology, specifically biochemistry, the formation of dipeptides refers to the process where two amino acids are linked together through a peptide bond. A peptide bond is formed in a dehydration synthesis reaction, where the carboxyl group of one amino acid reacts with the amino group of the second, releasing a molecule of water. The resulting dipeptide has a free amine group at one end and a free carboxyl group at the other, this allows for further peptide bonds to be formed if more amino acids are present.
When naming dipeptides, we use the three-letter abbreviations of the constituent amino acids, written from the N-terminus to the C-terminus. For instance, the dipeptide formed by glycine and alanine would be named Ala-Gly. The same principle applies to all other combinations of amino acids, resulting in a naming convention such as Pro-Thr for proline-threonine, Gly-Cys for glycine-cysteine, Ala-Ala for alanine-alanine, and Cys-Ala for cysteine-alanine.
Based on the question, any of these mentioned dipeptides can be formed depending on the availability of the respective amino acids. Therefore, options a. proline-threonine b. glycine-cysteine c. alanine-alanine d. cysteine-alanine are all possible dipeptides, each named according to the sequence of amino acids from N-terminus to C-terminus.