The true statement among the given options is: The human body uses 20 amino acids to form all types of proteins.
To clarify the other statements:
- Amino acids form a polypeptide chain via peptide bonds (specifically, covalent bonds between the amino group of one amino acid and the carboxyl group of another), not carbon-carbon bonds.
- tRNA (transfer RNA) is not attached to proteins in the cytoplasm; instead, it carries amino acids to the ribosome during protein synthesis.
- Amino acids must be assembled in a specific order determined by the mRNA sequence to form functional proteins.