Codon

Definition

A codon is a sequence of three nucleotides in DNA or RNA that corresponds to a specific amino acid or a stop signal during protein synthesis. Codons are fundamental to the process of translating genetic information from mRNA into proteins, linking the genetic code with the synthesis of polypeptides. They play a crucial role in determining the sequence of amino acids in proteins, which ultimately influences an organism's traits and functions.

5 Must Know Facts For Your Next Test

1. There are 64 possible codons, but only 20 standard amino acids, which means that some amino acids are specified by multiple codons, a phenomenon known as degeneracy.
2. Codons can be categorized into three types: sense codons that code for amino acids, start codons (AUG) that signal the beginning of translation, and stop codons (UAA, UAG, UGA) that signal the end of translation.
3. The genetic code is nearly universal, meaning that codons specify the same amino acids across most organisms, indicating a common evolutionary origin.
4. Mutations in codons can lead to changes in the amino acid sequence of proteins, which can have significant effects on protein function and may contribute to diseases.
5. Codon usage bias refers to the preference for certain codons over others in different organisms, which can influence the efficiency of protein synthesis and expression levels.

Review Questions

• How do codons contribute to the process of translating genetic information into functional proteins?
  • Codons are critical in translating genetic information because they encode specific amino acids during protein synthesis. Each set of three nucleotides in mRNA corresponds to an amino acid or a stop signal. As ribosomes read these codons during translation, they assemble the correct sequence of amino acids to form a protein. This process ensures that proteins are synthesized accurately according to the genetic instructions provided by the mRNA.
• Discuss the implications of codon mutations on protein function and potential effects on an organism.
  • Mutations in codons can lead to changes in the corresponding amino acids in proteins, which may alter their structure and function. For instance, if a mutation results in a premature stop codon, it could lead to a truncated protein that may not function correctly or at all. These alterations can have significant effects on cellular processes and may contribute to diseases such as cancer or genetic disorders. Understanding these implications helps in fields like genetics and medicine.
• Evaluate how codon usage bias can impact gene expression and the overall efficiency of protein synthesis in different organisms.
  • Codon usage bias refers to the preferential use of certain codons over others for encoding specific amino acids within an organism's genome. This bias can significantly influence gene expression levels and the efficiency of protein synthesis because tRNAs that correspond to more frequently used codons are typically more abundant. As a result, genes with optimal codon usage for a particular organism may be expressed more efficiently, leading to higher levels of protein production. This understanding is crucial for genetic engineering and synthetic biology applications, where optimizing gene expression is often a key objective.

Related terms

Amino Acid: The building blocks of proteins, amino acids are organic compounds that combine to form proteins and are encoded by codons.

Messenger RNA (mRNA): A type of RNA that carries genetic information from DNA to the ribosome, where it serves as a template for protein synthesis using codons.

Anticodon: A three-nucleotide sequence on transfer RNA (tRNA) that is complementary to a specific codon on mRNA, allowing for the correct amino acid to be added during translation.