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What Are Codons and Anticodons?

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A codon is a sequence of three nucleotides that comprise the foundation of messenger ribonucleic acid (mRNA). Anticodons are three-sequence nucleotides found in transfer RNA that complement codons in protein production.

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Background
Codons and anticodons combine in the process of protein synthesis, according to MCAT Prep. In the genetic code, this means the DNA is transcribed to the RNA before being synthesized by the ribosomes to create encoded genes. DNA is found in the nucleus and is the brain behind the information that becomes coded into genes. While inside the nucleus, the DNA is transcribed into mRNA. These new messenger RNA strands are then moved out of the nucleus and into the cytoplasm where ribosomes take these copies and make proteins. The result is encoded genes that are responsible for performing all the functions of the cell. During protein synthesis, the nucleobases A, C, G and U are used by cells.

Codons
In the production of mRNA, codons are responsible for creating the blueprint of amino acid sequences. Each codon is composed of three nucleotides and is degenerate, continuous and non-overlapping. Codons are considered degenerate because several codons work together to provide the complete code for amino acids. Codons are continuous because each three-sequence set is connected without any extra nucleotides in between. The three nucleotides do not overlap because they only serve in one codon and never as part of a separate codon. Codons are read from the first position at the five prime end to the third position at the three prime end.

Anticodons
Anticodons are three-segment nucleotides that correspond to codons. In DNA, anticodons are read backward in comparison to codons, starting at the three prime end and ending at the five prime end. These are found in the transfer RNA and help to align amino acids with the corresponding messenger RNA codons during protein production to build a complex protein or a polypeptide. Each nucleotide in anticodons can only be paired with one nucleotide in codons for proper performance. Mutations in codons and anticodons can result in improper amino acid connections and result in faulty cells, as claimed by the University of Massachusetts.

Protein Production
Once each nucleotide in codons and anticodons properly connects, the RNA polymerase creates an RNA strand that contains the blueprint of protein design. This messenger RNA then is then transferred to the ribosome where the actual protein-production process begins. As the codons and anticodons connect, enzymes bond amino acids together. The protein-synthesis process ends only when the ribosomes reach a stop codon, which signals the system to complete the translation process.

Pairing Rules
Every RNA nucleotide is designed to pair with only one other nucleotide. Bonds are created using hydrogen, and these bonds are the only way for DNA and RNA to successfully transfer information, as claimed by MCAT Prep. RNA is made of four bases known as adenine, cytosine, guanine and uracil. In molecular biology, these bases are often referred to by their initial letter. In RNA, the pairing rules mean that A nucleotides only bond with U and G nucleotides only bond with C nucleotides. In DNA, the uracil base doesn't exist and is replaced by thymine, which is more stable. This means that in DNA Adenine pairs with thymine and in RNA, Adenine pairs with uracil, notes by the International Society for Computational Biology.

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