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. This triplet code is essential for translating genetic information into proteins, as each codon matches with a corresponding tRNA molecule that carries the appropriate amino acid. The codon sequence ultimately determines the primary structure of proteins, which is vital for their function in cellular processes.
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There are 64 possible codons, including 61 that code for amino acids and 3 stop codons that signal the termination of protein synthesis.
Codons are read during translation in a sequential manner, ensuring that the correct amino acids are added to the growing polypeptide chain.
The genetic code is nearly universal, meaning that the same codons specify the same amino acids across almost all organisms, highlighting a shared evolutionary heritage.
Some amino acids are coded by more than one codon, a feature known as degeneracy, which provides a buffer against mutations that could alter protein function.
The start codon, AUG, not only initiates protein synthesis but also codes for the amino acid methionine, establishing the first amino acid in most proteins.
Review Questions
How do codons function in the process of translating genetic information into proteins?
Codons serve as the fundamental units of the genetic code during translation, where sequences of three nucleotides correspond to specific amino acids. During this process, ribosomes read the mRNA codons sequentially and recruit tRNA molecules that have complementary anticodons. Each tRNA carries its respective amino acid, allowing the ribosome to assemble them in the correct order to form a functional protein.
Discuss the significance of stop codons in protein synthesis and their role in determining protein structure.
Stop codons are critical in signaling the end of protein synthesis. They do not correspond to any amino acids but instead instruct the ribosome to release the completed polypeptide chain. The presence of stop codons ensures that proteins are synthesized to their precise length and composition as defined by the original mRNA template, directly influencing their final structure and function.
Evaluate how mutations affecting codon sequences can impact protein function and organismal health.
Mutations in codon sequences can lead to changes in amino acid composition within proteins, potentially altering their structure and function. For instance, a point mutation could result in a missense mutation where one amino acid is replaced with another, which might impair enzyme activity or alter cellular signaling pathways. In severe cases, such mutations can lead to diseases like sickle cell anemia or cystic fibrosis, showcasing how vital accurate codon sequences are for maintaining proper biological functions.
Related terms
anticodon: A sequence of three nucleotides in tRNA that is complementary to a specific codon in mRNA, allowing for accurate translation during protein synthesis.
amino acid: The building blocks of proteins, which are linked together by peptide bonds to form polypeptides based on the sequence determined by codons.
genetic code: The set of rules by which information encoded in genetic material (DNA and RNA sequences) is translated into proteins, with each codon specifying a particular amino acid.