The correct sequence of amino acids in proteins is directly determined by the sequence of nucleotides in the gene (DNA) that encodes the protein.
Proteins are essential for life, and their function relies heavily on their specific three-dimensional structure. This structure, in turn, is dictated by the precise order of amino acids that make up the protein chain. So how is this order determined? The answer lies within our DNA.
The Link Between DNA and Protein Sequence
Here's a more detailed explanation:
- DNA as the Blueprint: DNA contains the genetic code that provides the instructions for building proteins. The sequence of nucleotides (adenine, guanine, cytosine, and thymine) within a gene dictates the sequence of amino acids in a corresponding protein.
- Transcription and Translation: The process of converting DNA information into a protein involves two key steps:
- Transcription: The DNA sequence is transcribed into a messenger RNA (mRNA) molecule.
- Translation: The mRNA molecule then travels to ribosomes, which read the sequence and translate it into an amino acid chain using transfer RNA (tRNA) molecules, each carrying a specific amino acid.
- Codons and Amino Acids: The mRNA is read in triplets called codons. Each codon corresponds to a specific amino acid. For example, the codon "AUG" usually corresponds to the amino acid methionine.
- The Primary Structure: The order in which these codons appear in the mRNA determines the order in which amino acids are added to the growing protein chain. This sequence of amino acids forms the primary structure of the protein and ultimately determines the protein's three-dimensional shape and function.
Here's a table to summarize the process:
| Step | Description | Key Players | Outcome |
|---|---|---|---|
| DNA Code | Sequence of nucleotides in a gene. | DNA | Determines mRNA sequence |
| Transcription | Copying the DNA sequence into mRNA. | RNA Polymerase | Formation of mRNA molecule |
| Translation | mRNA sequence read and converted into an amino acid sequence. | Ribosomes, tRNA | Formation of the protein's amino acid sequence |
Importance of Sequence:
- A change in even a single nucleotide within the DNA can lead to a different codon in the mRNA, which in turn may result in the incorporation of a different amino acid in the protein.
- Such mutations can drastically alter the protein's function or cause it to become non-functional, demonstrating how precise the sequence of amino acids must be.
According to the provided reference, "The shape of a protein is determined by its primary structure (sequence of amino acids). The sequence of amino acids in a protein is determined by the sequence of nucleotides in the gene (DNA) encoding it."
