The sequence of __ in mRNA determines the sequence of amino acids in a polypeptide chain.
A codons
B promoters
C ribosomes
D anticodons
The correct answer and explanation is:
The correct answer is A) codons.
In the process of protein synthesis, the sequence of codons in mRNA plays a critical role in determining the sequence of amino acids in a polypeptide chain. A codon is a set of three nucleotides in mRNA that codes for a specific amino acid. Each codon corresponds to one of the 20 standard amino acids used in proteins. The genetic code is universal and is read in triplets of nucleotides called codons.
The process begins with transcription, where a section of DNA is used as a template to produce a complementary strand of mRNA. The mRNA strand then carries this genetic information to the ribosome, the site of translation. Translation involves the conversion of the genetic information into a sequence of amino acids.
During translation, the ribosome reads the mRNA in sets of three nucleotides (codons). For example, the codon AUG codes for the amino acid methionine, which also serves as the start signal for protein synthesis. Transfer RNA (tRNA) molecules have anticodons that are complementary to the codons in the mRNA. Each tRNA carries a specific amino acid that corresponds to the codon it pairs with. As the ribosome moves along the mRNA, the tRNA molecules bring the appropriate amino acids, and these are joined together to form a polypeptide chain.
Thus, the sequence of codons in the mRNA determines the sequence of amino acids, which ultimately dictates the structure and function of the resulting protein. This process is central to the expression of genetic information and the synthesis of proteins that carry out various functions in the cell.