![]() ![]() In the box where the first and second bases intersect, you find the third base (G), which is shown in purple. Then, you identify the second base (C), which is shown in green. To use the square table, you begin with the first base (A), which shown in red. After transcription, the mRNA produced would have the sequence ACG. This example shows how to use both tables to determine the amino acid coded for by the DNA sequence TGC. If you are given a DNA sequence, you must first transcribe it to produce the mRNA, then you can translate it into an amino acid sequence using the codon table.įigure 9 shows two different codon tables: one square, and one round. Using the Codon TableĬodon tables, such as the one in Figure 8, give the amino acids that are coded for by mRNA codons, not DNA codons. With a few exceptions, virtually all species use the same genetic code for protein synthesis, which is powerful evidence that all life on Earth shares a common origin. The reading frame for translation is set by the AUG start codon near the 5′ end of the mRNA. In addition to specifying the amino acid methionine, it also serves as the start codon to initiate translation. Another codon, AUG, also has a special function. Three of the 64 codons terminate protein synthesis and release the polypeptide from the translation machinery. ![]() Figure 8: This figure shows the genetic code for translating each nucleotide triplet, or codon, in mRNA into an amino acid or a termination signal in a nascent protein. Using a three-nucleotide code means that there are a total of 64 (4 × 4 × 4) possible combinations therefore, a given amino acid is encoded by more than one nucleotide triplet ( Figure 8). Given the different numbers of “letters” in the mRNA and protein “alphabets,” combinations of nucleotides corresponded to single amino acids. The relationship between a nucleotide codon and its corresponding amino acid is called the genetic code. Each amino acid is defined by a three-nucleotide sequence called the triplet codon. Protein sequences consist of 20 commonly occurring amino acids therefore, it can be said that the protein alphabet consists of 20 letters. Translation of the mRNA template converts nucleotide-based genetic information into a protein product. To summarize what we know to this point, the cellular process of transcription generates messenger RNA (mRNA), a mobile molecular copy of one or more genes with an alphabet of A, C, G, and uracil (U). ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |