The relationship between amino acids and DNA is very important in the mechanism by which genetic information is converted into proteins: DNA contains the sequence information of amino acids for each gene, and based on this information, amino acids are combined to form a specific protein. The process of converting genetic information from DNA to protein involves the action of messenger RNA called mRNA.
Relationship between DNA and amino acids
- Codons and Amino Acids
- The base sequence of DNA determines the sequence of amino acids that make up proteins. When this sequence is transcribed into mRNA, the combination of three bases forms a unit called a “codon. A codon corresponds to one of 20 different amino acids; for example, the codon “AUG” designates methionine.
- Translation and amino acid sequence
- As mRNA is read by ribosomes and tRNA carries amino acids, the amino acids are arranged in a specific order to form a polypeptide chain (protein). Thus, genetic information stored in DNA is translated into a specific protein through the sequence of amino acids.
Stop codon (termination codon)
A stop codon (termination codon) is a special codon that signals the end of protein synthesis and is one of the three termination codons (UAA, UAG, UGA) located on the mRNA. These codons have no tRNA counterparts in the amino acids, so when the ribosome reads them, translation stops and elongation of the polypeptide chain is terminated.
- Role of Stop Codons
Stop codons are set to ensure that the protein ends at the required length, preventing unnecessary amino acids from being added. Without stop codons in the appropriate positions, abnormally long proteins are produced that may not function or may even be detrimental. - Termination of Translation
Upon reaching the stop codon, the ribosome leaves the polypeptide chain and the completed protein is released from the ribosome. This results in the production of a protein that accurately reflects the information encoded in the mRNA.
A list of codons and their corresponding amino acids is shown below. A codon is a sequence of three bases, 64 in total, of which 61 correspond to 20 different amino acids. The remaining three are stop codons (termination codons), which are responsible for signals that terminate protein synthesis.
Codon and Amino Acid Correspondence Table
| Codon | Amino Acid | Codon | Amino Acid | Codon | Amino Acid | Codon | Amino Acid |
|---|---|---|---|---|---|---|---|
| UUU | Phenylalanine (Phe) | UCU | Serine (Ser) | UAU | Tyrosine (Tyr) | UGU | Cysteine (Cys) |
| UUC | Phenylalanine (Phe) | UCC | Serine (Ser) | UAC | Tyrosine (Tyr) | UGC | Cysteine (Cys) |
| UUA | Leucine (Leu) | UCA | Serine (Ser) | UAA | (Stop) | UGA | (Stop) |
| UUG | Leucine (Leu) | UCG | Serine (Ser) | UAG | (Stop) | UGG | Tryptophan (Trp) |
| CUU | Leucine (Leu) | CCU | Proline (Pro) | CAU | Histidine (His) | CGU | Arginine (Arg) |
| CUC | Leucine (Leu) | CCC | Proline (Pro) | CAC | Histidine (His) | CGC | Arginine (Arg) |
| CUA | Leucine (Leu) | CCA | Proline (Pro) | CAA | Glutamine (Gln) | CGA | Arginine (Arg) |
| CUG | Leucine (Leu) | CCG | Proline (Pro) | CAG | Glutamine(Gln) | CGG | Arginine (Arg) |
| AUU | Isoleucine (Ile) | ACU | Threonine (Thr) | AAU | Asparagine (Asn) | AGU | Serine (Ser) |
| AUC | Isoleucine (Ile) | ACC | Threonine (Thr) | AAC | Asparagine (Asn) | AGC | Serine (Ser) |
| AUA | Isoleucine (Ile) | ACA | Threonine (Thr) | AAA | Lysine (Lys) | AGA | Arginine (Arg) |
| AUG | Methionine (Met) | ACG | Threonine (Thr) | AAG | Lysine (Lys) | AGG | Arginine (Arg) |
| GUU | Valine (Val) | GCU | Alanine (Ala) | GAU | Aspartic acid (Asp) | GGU | Glycine (Gly) |
| GUC | Valine (Val) | GCC | Alanine (Ala) | GAC | Aspartic acid (Asp) | GGC | Glycine (Gly) |
| GUA | Valine (Val) | GCA | Alanine (Ala) | GAA | Glutamic acid (Glu) | GGA | Glycine (Gly) |
| GUG | Valine (Val) | GCG | Alanine (Ala) | GAG | Glutamic acid (Glu) | GGG | Glycine (Gly) |
Special Note
- Start codon: “AUG” specifies methionine (Met) and indicates the start of protein synthesis.
- Termination codons: UAA, UAG, and UGA are signals to terminate protein synthesis. The termination codon has no corresponding amino acid, so translation ends here.
This table shows which amino acids correspond to which codons in mRNA, and reveals how the information encoded in DNA is embodied in the amino acid sequence.
Conclusion
DNA contains amino acid sequence information, which is transcribed into mRNA in codon units and read by ribosomes to synthesize proteins. The stop codon acts as a signal to indicate the end of this protein synthesis and is essential for the precise production of a protein of the required length. Through this series of processes, information in DNA is converted into the proteins that are fundamental to life.
