Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Translation is the process where the sequence of nucleotides in is translated into the sequence of amino acids in a polypeptide chain.
The process occurs in the cytoplasm on ribosomes, moving in the direction along the .
Aminoacylation (Charging of ): Before translation, amino acids are activated in the presence of and linked to their cognate , a process catalyzed by aminoacyl- synthetase.
Ribosome Structure: Consists of two subunits. The small subunit binds the , while the large subunit has two sites (-site and -site) for binding and contains the enzyme peptidyl transferase ( in bacteria).
Initiation: The small subunit binds to at the start codon (). The initiator (carrying ) binds to the -site.
Elongation: New aminoacyl- complexes bind to the -site. A peptide bond is formed between the amino acid at the -site and the one at the -site.
Termination: Occurs when a stop codon (, , or ) reaches the -site. Release factors bind to the stop codon, terminating translation and releasing the polypeptide.
Untranslated Regions (UTRs): These are sequences of located before the start codon (at end) and after the stop codon (at end) that are not translated but are required for efficient translation.
📐Formulae
💡Examples
Problem 1:
A segment of has the sequence . Determine the number of amino acids in the resulting polypeptide chain and identify the effect of the codon.
Solution:
The polypeptide will consist of amino acids.
Explanation:
The codons are (Methionine), (Phenylalanine), and (Aspartic acid). The fourth codon, , is a stop codon (nonsense codon) which does not code for any amino acid and signals the termination of translation. Therefore, only amino acids are polymerized.
Problem 2:
Explain the role of during the elongation phase of translation in prokaryotes.
Solution:
It acts as a ribozyme (peptidyl transferase).
Explanation:
In bacteria, the molecule in the large ribosomal subunit functions as an enzyme called peptidyl transferase, which catalyzes the formation of a peptide bond between the amino acids located at the and sites.