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. Each codon is part of the genetic code, which dictates how sequences of nucleotides are translated into proteins. This process is essential for expressing genes and ultimately determines the function of proteins within an organism.

5 Must Know Facts For Your Next Test

1. There are 64 possible codons, but only 20 different amino acids, meaning that some amino acids are encoded by multiple codons, a feature known as redundancy.
2. Codons can be classified into two types: sense codons, which code for amino acids, and stop codons, which signal the termination of protein synthesis.
3. The start codon, AUG, not only initiates translation but also codes for the amino acid methionine, making it a vital component in protein synthesis.
4. In eukaryotes, codons are read by ribosomes during translation, with transfer RNA (tRNA) bringing the corresponding amino acids to the growing polypeptide chain based on the codon sequence.
5. Mutations in codons can lead to changes in protein function; these mutations can be silent (no effect), missense (one amino acid change), or nonsense (premature stop codon).

Review Questions

• How do codons relate to the process of translating genetic information into proteins?
  • Codons play a central role in translating genetic information into proteins by serving as the basic units of the genetic code. Each codon consists of three nucleotides that specify a particular amino acid or a stop signal. During translation, ribosomes read these codons in sequence on the mRNA strand and use transfer RNA (tRNA) to bring the correct amino acids together to form a polypeptide chain. This process highlights how codons directly influence the structure and function of proteins.
• Discuss the implications of codon redundancy in protein synthesis and its potential effects on genetic mutations.
  • Codon redundancy, where multiple codons encode the same amino acid, has significant implications for protein synthesis and genetic mutations. This feature can buffer against certain types of mutations; for example, if a mutation occurs in a codon but results in the same amino acid being produced due to redundancy, the protein's function may remain unaffected. However, not all mutations are harmless; changes to critical codons can lead to missense or nonsense mutations that alter protein structure and function, potentially causing diseases.
• Evaluate the role of start and stop codons in regulating gene expression and protein synthesis.
  • Start and stop codons are crucial for regulating gene expression and ensuring proper protein synthesis. The start codon (AUG) not only signals the beginning of translation but also codes for methionine, establishing the first amino acid in the polypeptide chain. Conversely, stop codons signal termination of translation, ensuring that protein synthesis occurs correctly and efficiently. Together, these codons help maintain fidelity during protein synthesis and prevent errors that could lead to nonfunctional or harmful proteins, thus playing a key role in cellular function.

Related terms

Amino Acid: The building blocks of proteins, amino acids are organic compounds that combine to form proteins. Each amino acid is specified by one or more 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, with codons determining the sequence of amino acids.

Genetic Code: The set of rules by which information encoded in genetic material is translated into proteins, consisting of codons that specify the amino acid sequence.