Final answer:
The correct answer to the question is A) Codon, which is a sequence of three nucleotides on an mRNA molecule corresponding to a specific amino acid or signal in protein synthesis.
Step-by-step explanation:
The group of three nitrogen bases in the mRNA message that is read together is called a codon. Therefore, the correct answer is A) Codon. A codon is a consecutive sequence of three nucleotides on an mRNA molecule that corresponds to a specific amino acid or a start or stop signal during the process of translation, where proteins are synthesized. This is a fundamental component of the genetic code, where each codon 'word' represents one of the twenty standard amino acids or a signal to begin or cease protein synthesis.
To further clarify the terms from the question, an anticodon is a consecutive sequence of three nucleotides on a tRNA molecule that is complementary to a specific codon on an mRNA molecule. A chromosome is a long DNA molecule that contains many genes. A nucleotide is the basic building block of nucleic acids, like DNA and RNA, and consists of a nitrogenous base, a sugar, and a phosphate group, but it does not form a codon on its own—it takes three of these units to create one.
If we put the following units in order from the smallest to the largest: codon, gene, nitrogen base, nucleotide, and chromosome, we get the sequence: C) nitrogen base, D) nucleotide, E) codon, B) gene, A) chromosome.