Describe the process of translation (initiation, elongation, termination) Flashcards
1
Q
Initiation translation
A
- Translation begins when the small and large subunits of the ribosome bind to the 5’ cap of the mRNA molecule.
- The ribosome scans the mRNA to locate the start codon (AUG), which sets the reading frame for translation.
- The start codon corresponds to methionine, the first amino acid in the polypeptide chain.
- A transfer RNA (tRNA) with the complementary anticodon (UAC) binds to the start codon, delivering methionine.
2
Q
Elongating the polypeptide chain
A
- The ribosome has three binding sites for tRNA: the A site (acceptor or aminoacyl), the P site (peptidyl), and the E site (exit).
1. An aminoacyl-tRNA binds to the A site.
2. Peptidyl transferase cleaves the amino acid from the P site tRNA and bonds it to the amino acid on the A site tRNA, forming a peptide bond and elongating the polypeptide chain.
3. The ribosome moves along the mRNA to the next codon, bringing the tRNA with the polypeptide to the P site and moving the empty tRNA to the E site to exit.
4. After the ribosome moves over one codon, the empty tRNA in the E site is released, and the cycle is ready to start again. If a stop codon is reached, a release factor binds to the ribosome, causing the release of the finished polypeptide.
3
Q
Termination of protein synthesis
A
- Translation ends when the ribosome encounters a stop codon (UAG, UGA, or UAA) on the mRNA.
- No tRNA matches the stop codons; instead, a release factor binds to the ribosome, signaling it to release the newly synthesized polypeptide chain.
- The ribosome disassembles, and the polypeptide folds into its functional three-dimensional structure.