20. Which of these is the smallest structure?
A. Dipeptide
B. Polypeptide
C. Protein
D. Amino acid
To determine the smallest structure among the options given, let's break down each term:
A. Dipeptide: A dipeptide is formed when two amino acids join together by a peptide bond. It consists of two amino acids bonded together.
B. Polypeptide: A polypeptide is a polymer made up of multiple amino acids bonded together by peptide bonds. It can vary in length, ranging from just a few amino acids to thousands.
C. Protein: A protein is a macromolecule composed of one or more polypeptide chains. Proteins have complex three-dimensional structures and are involved in various biological functions.
D. Amino acid: An amino acid is the basic building block of proteins. It consists of an amino group, a carboxyl group, a hydrogen atom, and a unique side chain (R-group).
Based on these definitions, we can see that the smallest structure among the options is an amino acid (choice D). Amino acids are the individual units that come together to form dipeptides, polypeptides, and ultimately proteins.