protein synthesis

• Gene

  A sequence of nucleotide bases in a DNA molecule that codes for the production of a specific sequence of amino acids, that in turn make up a specific polypeptide (protein)
• Protein synthesis

  1. Transcription

  2. Translation
• Transcription

  DNA is transcribed and an mRNA molecule is produced
• Transcription

  • Occurs in the nucleus of the cell
  • Produces an mRNA copy of a section of DNA known as a gene
• Transcription process

  1. Part of the DNA molecule unwinds

  2. Exposes the template strand of the gene that codes for the protein being synthesised

  3. Free mRNA nucleotides that are present in the nucleus bind to complementary nucleotides on the template strand

  4. The mRNA nucleotides are joined to neighbouring nucleotides, forming a single strand of mRNA

  5. The mRNA molecule leaves the nucleus via a pore in the nuclear envelope
• The new strand of mRNA is a complementary copy of the DNA code from the original gene
• Translation

  The stage of protein synthesis that occurs in the cytoplasm of the cell, and results in the production of a chain of amino acids that will go on to form a protein
• Gene

  A copy of a section of DNA that codes for a protein
• Transcription

  1. Part of the DNA molecule unwinds

  2. Hydrogen bonds between complementary base pairs break

  3. Template strand of the gene that codes for the protein being synthesised is exposed

  4. Free mRNA nucleotides in the nucleus bind to complementary nucleotides on the template strand

  5. mRNA nucleotides are joined to neighbouring nucleotides, forming a single strand of mRNA

  6. mRNA molecule leaves the nucleus via a pore in the nuclear envelope

  7. New strand of mRNA is a complementary copy of the DNA code from the original gene
• Translation

  Stage of protein synthesis that occurs in the cytoplasm and results in the production of a chain of amino acids that will form a protein
• Translation

  1. mRNA molecule attaches to a ribosome

  2. tRNA molecules with a triplet of unpaired bases (anticodon) and an amino acid at the other end bind to complementary triplets (codons) on the mRNA molecule

  3. A peptide bond is formed between the two neighbouring amino acids

  4. This process continues until a 'stop' codon on the mRNA molecule is reached, signalling translation to stop and the amino acid chain is complete

  5. The amino acid chain is then folded and modified to form the final protein molecule
• mRNA

  • Carries the genetic code from the nucleus to the ribosomes in the cytoplasm
• Ribosomes

  • Sites of protein synthesis in the cytoplasm
• Codons

  Triplets of bases on the mRNA molecule that correspond to specific amino acids
• Anticodons


  Triplets of unpaired bases on tRNA molecules that bind to complementary codons on the mRNA molecule