Codon

Definition

A codon is a sequence of three nucleotides in messenger RNA (mRNA) that specifies a particular amino acid or a stop signal during protein synthesis. Each codon corresponds to a specific amino acid, forming the genetic code that dictates how proteins are assembled from amino acids, connecting to the formation of peptide bonds between those amino acids.

5 Must Know Facts For Your Next Test

1. There are 64 possible codons, including 61 that code for amino acids and 3 stop codons that signal the end of protein synthesis.
2. The genetic code is nearly universal across all organisms, meaning that a codon typically encodes the same amino acid in different species.
3. Codons are read in a non-overlapping manner during translation; once a codon is read, the ribosome moves on to the next one without skipping any nucleotides.
4. The redundancy in the genetic code means that some amino acids can be specified by more than one codon, which helps protect against mutations.
5. Start codons (like AUG) not only specify an amino acid but also signal the beginning of translation for protein synthesis.

Review Questions

• How do codons determine the sequence of amino acids in a protein?
  • Codons, made up of three nucleotides each, directly dictate which amino acids will be added during protein synthesis. When mRNA is translated at the ribosome, each codon is matched with its corresponding transfer RNA (tRNA), which carries the specific amino acid. This sequence continues until all codons have been read, creating a polypeptide chain that ultimately folds into a functional protein.
• Discuss the significance of start and stop codons in protein synthesis.
  • Start and stop codons are crucial for initiating and terminating the process of translation. The start codon, typically AUG, signals the ribosome to begin assembling the amino acids into a protein. Stop codons do not specify an amino acid but instead instruct the ribosome to halt translation once a complete polypeptide has been formed. This ensures that proteins are synthesized accurately and at the right length.
• Evaluate how mutations in codons can impact protein function and organismal traits.
  • Mutations in codons can lead to changes in the amino acid sequence of proteins, potentially altering their structure and function. For example, if a mutation changes a codon from coding for one amino acid to another, it could result in a nonfunctional protein or one with altered activity. Such changes can affect an organism's traits and might contribute to diseases or adaptive advantages, highlighting the critical role that accurate coding plays in biological systems.

Related terms

Amino Acid: Organic compounds that serve as the building blocks of proteins, linked together by peptide bonds.

mRNA: Messenger RNA, which carries genetic information from DNA to the ribosome, where proteins are synthesized.

Ribosome: A molecular machine in the cell that facilitates the translation of mRNA into a polypeptide chain, assembling amino acids based on codon sequences.