Translation Process in Cells

Key Terms

Codon: Three-base sequence in messenger RNA (mRNA) designating amino acids.
Anticodon: Complementary three-base sequence in transfer RNA (tRNA) that pairs with the codon.
Start Codon: Always AUG; encodes methionine, the first amino acid of a protein.
- In bacteria, often a formylmethionine is used.
Nonsense Codon (Stop Codon): One of three codons that signal the ribosome to stop translation.
Polypeptide Elongation: Process of adding amino acids to a growing chain until a stop codon is reached.
tRNA: Brings amino acids to the ribosome using its anticodon.
rRNA: Structural component of the ribosome.

P Site (Peptidyl Site): Holds the tRNA with the growing polypeptide chain.
A Site (Aminoacyl Site): Accepts incoming tRNA carrying the next amino acid.
E Site (Eject Site): Where uncharged tRNA exits the ribosome.

Large and small ribosomal subunits assemble at the start codon (AUG) with the first methionine-carrying tRNA.
The initiation complex forms with tRNA starting in the P-site.

Aminoacyl-tRNAs enter the A-site.
Peptide bonds form between adjacent amino acids (e.g., methionine and leucine).
Ribosome translocates along the mRNA, shifting tRNAs from the A-site to the P-site, and P-site to the E-site.
Process repeats as codons are read and corresponding amino acids are added.

mRNA can encode multiple copies of the same protein.
Longevity of mRNA impacts protein production.
In eukaryotes, mRNA is synthesized in the nucleus, then exits to the cytoplasm for translation.

Prokaryotes:
- Transcription and translation occur simultaneously in the cytoplasm.
- Quick doubling time due to simultaneous processes.
Eukaryotes:
- mRNA transcription in the nucleus, translation in the cytoplasm.
- mRNA requires processing (e.g., intron removal) before translation.

This efficient simultaneous process gives bacteria an edge over eukaryotes in terms of reproduction speed.

The lecture also referenced a visual animation illustrating the processes of transcription and translation.