Protein Synthesis Overview

Key Terms and Concepts

• Transcription: The process of converting DNA to mRNA in the nucleus.
• Translation: The process of converting mRNA into a polypeptide chain (protein) at the ribosome.
• DNA: The genetic material located in the nucleus that serves as a template for transcription.
• mRNA (messenger RNA): The RNA copy of a gene used as a template for protein synthesis during translation.
• RNA Polymerase: The enzyme responsible for reading DNA and synthesizing mRNA during transcription.
• Introns: Non-coding sequences in mRNA that are removed before translation.
• Exons: Coding sequences in mRNA that are spliced together after introns are removed and are involved in protein synthesis.
• Ribosome: The cellular machinery where translation occurs, decoding mRNA into a polypeptide.
• tRNA (transfer RNA): The RNA that carries amino acids to the ribosome and matches them to the coded mRNA message via anticodons.
• Amino Acid: The building blocks of proteins, linked together during translation to form polypeptides.
• Polypeptide: A chain of amino acids that folds into a functional protein.
• Nucleus: The organelle in eukaryotic cells where transcription takes place.
• Codon: A sequence of three nucleotides on mRNA that codes for a specific amino acid or a start/stop signal during translation.
• Anticodon: A sequence of three nucleotides on tRNA that pairs with a complementary codon in mRNA during translation.

Protein Synthesis Process

Transcription (Occurs in the Nucleus)

1. Initiation:
   • RNA Polymerase binds to a specific region called the promoter on the DNA.
2. Elongation:
   • RNA Polymerase reads the DNA template strand and synthesizes a complementary mRNA strand.
3. Termination:
   • RNA Polymerase reaches a termination signal, and the mRNA strand is released.

mRNA Processing

• Splicing:
  • Introns are removed, and exons are joined to form a mature mRNA strand.
• Capping and Polyadenylation:
  • A 5' cap and a 3' poly-A tail are added to mRNA for stability and export from the nucleus.

Translation (Occurs in the Ribosome)

1. Initiation:
   • mRNA attaches to the small subunit of the ribosome.
   • The start codon (AUG) is recognized by a corresponding tRNA with the anticodon UAC.
2. Elongation:
   • tRNA brings specific amino acids to the ribosome, matching codons on mRNA with anticodons.
   • Amino acids are linked together by peptide bonds to form a growing polypeptide chain.
3. Termination:
   • A stop codon (UAA, UAG, UGA) is reached on the mRNA.
   • The completed polypeptide is released from the ribosome.