The three-base sequence on DNA that codes for an amino acid is called a/an

A. nucleotide: A nucleotide is the basic structural unit of DNA and RNA, consisting of a sugar, phosphate group, and nitrogenous base. While nucleotides make up the DNA sequence, a group of three bases does not code for a single nucleotide but rather for an amino acid.

B. amino acid: A codon, composed of three consecutive nucleotide bases in DNA or RNA, specifies a single amino acid during protein synthesis. For example, the DNA triplet ATG codes for the amino acid methionine. This triplet code is universal and ensures accurate translation from genetic information to functional proteins.

C. purine: Purines, such as adenine and guanine, are types of nitrogenous bases. They are part of nucleotides, but a triplet of bases does not directly correspond to a single purine; instead, codons dictate amino acids.

D. protein: Proteins are composed of long chains of amino acids. While codons ultimately determine the sequence of amino acids that form a protein, each codon specifies only one amino acid, not an entire protein.

A. Vaccination: Vaccination involves the introduction of a harmless or weakened pathogen, or part of a pathogen, into the body to stimulate an immune response without causing the disease itself. In this example, exposure to cowpox, a virus similar to smallpox but much less virulent, trains the immune system to recognize and respond to smallpox, providing protective immunity. This principle forms the basis of immunization.

B. Antibiotic resistance: Antibiotic resistance occurs when bacteria evolve mechanisms to survive exposure to antibiotics that would normally kill them or inhibit their growth. It is unrelated to viral exposure or immune system training, and thus does not explain immunity following cowpox exposure.

C. Sterilization: Sterilization is the complete destruction of all microorganisms, including spores, on inanimate objects. It is a physical or chemical process used to prevent infection but does not confer immunity or involve the immune system. Therefore, sterilization does not explain the protective effect observed in the child exposed to cowpox.