Protein Synthesis

• The Genetic Code

  • the way that the 4 nitrogenous bases are ordered
  • set of 3 DNA nucleotides = triplet
  • mRNA triplet = codon
• Materials Needed for Protein Synthesis

  • codons
  • amino acids
  • enzymes
  • nucleic acids
• Protein Synthesis

  • a process where cells produce proteins from instructions encoded in genes found in the coding section of the cell's DNA
  • only 1 of 2 strands is used for transcription
• Transcription is the process of copying a segment of DNA into RNA
• Transcription Initiation:

  • RNA polymerase binds to the promoter region at the beginning of the gene
  • Weak hydrogen bonds between complementary bases are broken by RNA polymerase to unzip the gene
• Transcription Elongation:

  • RNA polymerase reads the base sequence of the template strand of DNA to produce a strand of mRNA
  • RNA polymerase moves along the DNA molecule in a 3' to 5' direction building a strand of mRNA out of complementary nucleotides
  • Thymine is replaced with uracil, mRNA is synthesized in a 5' to 3' direction
• Transcription Termination:

  • The process continues until RNA polymerase reaches a termination signal (stop codon) and the pre-mRNA is released
  • Hydrogen bonds form and DNA zips back up
  • Introns are removed from the mRNA and exons are joined to create a mature mRNA molecule
  • mRNA leaves the nucleus through a nuclear pore
• Translation Initiation

  • the short, single-stranded mRNA leaves the nucleus via a nuclear pore
  • the ribosome binds to the mRNA strand
  • a start codon (AUG) signals for a tRNA molecule with a complementary anticodon to arrive for base pairing and binds to the P site on the ribosome
• Translation Elongation

  • a tRNA molecule, which includes an anticodon, is attracted to the corresponding codon due to complementary base pairing
  • on the other side of the tRNA molecule is the amino acid specified by the codon
  • as one codon is read and exits, another one slides into the ribosome to be read
  • tRNAs transfer the amino acids to the mRNA
• Translation Termination

  • when a stop codon appears, elongation ceases, and the polypeptide is released from the ribosome
  • ribosome separates from the mRNA
  • translation is complete, the polypeptide either folds to form a protein or joins with another polypeptide to fold to become a 3D protein ready to perform a function
• amino acids are linked together by peptide bonds to form polypeptide chains