During protein synthesis, the DNA code is transcribed into a complementary strand of messenger RNA (mRNA) through a process called transcription. This mRNA strand then carries the genetic information from the nucleus of the cell to the ribosomes, where it serves as a template for protein synthesis. The mRNA code consists of three-nucleotide sequences called codons, each of which specifies a particular amino acid or a stop signal.
The relationship between the DNA code and the mRNA code is as follows:
1. Transcription: During transcription, an enzyme called RNA polymerase reads the DNA sequence in the nucleus and synthesizes a complementary mRNA molecule. Each DNA nucleotide base is transcribed into its complementary RNA base, with the exception of thymine (T), which is replaced by uracil (U) in mRNA.
2. Codons: The mRNA sequence is composed of codons, which are triplets of nucleotides that code for specific amino acids. There are 64 possible codons, 61 of which encode amino acids, while the remaining three are stop codons that signal the end of protein synthesis.
3. Translation: When the mRNA molecule reaches the ribosome, it is translated into a sequence of amino acids. The ribosome reads the codons one by one and matches them with their complementary transfer RNA (tRNA) molecules. Each tRNA molecule carries an amino acid specific to its codon.
4. Protein Synthesis: As the tRNA molecules bring amino acids to the ribosome, peptide bonds are formed between them, creating a growing polypeptide chain. The sequence of amino acids in the polypeptide chain is determined by the sequence of codons in the mRNA.
In summary, the code of mRNA is directly dependent upon the sequence of nucleotides in DNA. DNA serves as the master template, and through the processes of transcription and translation, the genetic information is transferred from DNA to mRNA and ultimately into the synthesis of proteins.
