Protein Synthesis and Ribosomes

Ribosome Structure

• Small Subunit: Responsible for reading the mRNA.
• Large Subunit: Joins amino acids to form a polypeptide chain.

Overview of Protein Synthesis

• Process: Proteins are synthesized through a process called translation, which occurs at the ribosome.
• mRNA Role: Messenger RNA (mRNA) is a copy of the DNA strand that carries the genetic instructions from the nucleus to the ribosome.

Translation Process

1. mRNA Arrival: The mRNA strand arrives at the ribosome after being transcribed from DNA.
2. Codons: The mRNA sequence is divided into codons (groups of three nucleotides).
   • Each codon specifies a single amino acid.
   • E.g., GAA codes for Glutamic Acid, AAA codes for Lysine.

Amino Acids and Codons

• Each codon corresponds to an amino acid in the growing polypeptide chain.
• List of Amino Acids and their corresponding Codons:
  • Valine (Val) - GUU, GUC, GUA, GUG
  • Arginine (Arg) - CGU, CGC, CGA, CGG, AGA, AGG
  • Serine (Ser) - UCU, UCC, UCA, UCG, AGU, AGC
  • Lysine (Lys) - AAA, AAG
  • Alanine (Ala) - GCU, GCC, GCA, GCG
  • Aspartic Acid (Asp) - GAU, GAC
  • Glutamic Acid (Glu) - GAA, GAG
  • Glycine (Gly) - GGU, GGC, GGA, GGG
  • Cysteine (Cys) - UGU, UGC
  • Proline (Pro) - CCU, CCC, CCA, CCG
  • Threonine (Thr) - ACU, ACC, ACA, ACG
  • Methionine (Met) - AUG (Start Codon)
  • Isoleucine (Ile) - AUU, AUC, AUA
  • Histidine (His) - CAU, CAC
  • Glutamine (Gln) - CAA, CAG
  • Tyrosine (Tyr) - UAU, UAC
  • Stop Codons - UAA, UAG, UGA

Translation Mechanism

• Decoding: The ribosome reads the mRNA codons starting from the Start Codon (AUG) and moves through the mRNA strand to the Stop Codons, which signal the end of the protein chain.
• Example Codon Translations:
  • GAA = Glutamic Acid
  • AAA = Lysine

Key Points

• Each codon corresponds to one amino acid, highlighting the genetic code's specificity in protein synthesis.
• Ribosomes are essential for translating mRNA into functional proteins, a crucial process in cellular biology.