Stages of Protein Synthesis to Know for Biological Chemistry I

Protein synthesis is a vital process in biological chemistry, transforming genetic information into functional proteins. It involves several stages: transcription, translation, and post-translational modifications, each crucial for producing proteins that support cellular functions and overall metabolism.

1. Transcription

   • The process of synthesizing RNA from a DNA template, primarily occurring in the nucleus.
   • Involves the enzyme RNA polymerase, which unwinds the DNA and assembles RNA nucleotides complementary to the DNA strand.
   • Results in the formation of messenger RNA (mRNA), which carries genetic information from DNA to the ribosome.

2. Post-transcriptional modifications

   • mRNA undergoes several modifications before it can be translated, including the addition of a 5' cap and a poly-A tail.
   • Introns (non-coding regions) are removed, and exons (coding regions) are spliced together to form a mature mRNA molecule.
   • These modifications enhance mRNA stability, facilitate export from the nucleus, and improve translation efficiency.

3. Translation initiation

   • The assembly of the ribosome at the start codon (AUG) on the mRNA, marking the beginning of protein synthesis.
   • Involves the recruitment of the initiator tRNA, which carries the amino acid methionine, to the ribosome.
   • Requires several initiation factors and energy in the form of GTP to ensure proper assembly and positioning.

4. Translation elongation

   • The ribosome moves along the mRNA, reading codons and facilitating the addition of amino acids to the growing polypeptide chain.
   • Transfer RNA (tRNA) molecules bring specific amino acids to the ribosome, matching their anticodons with the mRNA codons.
   • Peptide bonds form between adjacent amino acids, catalyzed by the ribosomal RNA (rRNA) within the ribosome.

5. Translation termination

   • Occurs when a stop codon (UAA, UAG, or UGA) is reached on the mRNA, signaling the end of protein synthesis.
   • Release factors bind to the ribosome, prompting the release of the newly synthesized polypeptide chain.
   • The ribosomal subunits disassemble, and the mRNA is released for potential reuse or degradation.

6. Post-translational modifications

   • Newly synthesized proteins often undergo modifications such as phosphorylation, glycosylation, and ubiquitination, which can affect their function and activity.
   • These modifications can regulate protein stability, localization, and interactions with other molecules.
   • Post-translational modifications are crucial for the proper functioning of proteins and can play significant roles in cellular signaling and metabolism.