transcription and translation

• This process of protein synthesis occurs in two stages

  • Transcription – DNA is transcribed and an mRNA molecule is produced
  • Translation – mRNA (messenger RNA) is translated and an amino acid sequence is produced
• • Transcription occurs in the nucleus and produces shorter molecules of RNA.
• Transcription occurs in the nucleus and produces shorter molecules of RNA.

  • A section of a DNA molecule unwinds and unzips, using DNA Helicase.
  • The strand that runs 3’ to 5’ is known as the antisense strand and acts as a template for transcription.
  • Free RNA nucleotides pair to their complementary base on the antisense strand. (Uracil, not thymine)
  • RNA Polymerase forms phosphodiester bonds
  • At the end of the gene the completed RNA strand is called mRNA and detaches and leaves the nucleus.

  
• Translation occurs in the ribosome and results in the production of tRNA and then a polypeptide

  
• translation -

  1. mRNA binds to the small subunit on the ribosome and tRNA with a complementary anticodon to the start codon of AUG binds
  2. This tRNA carries an amino acid called Methionine
  3. tRNA with the anticodon UGC with the amino acid threonine binds to ACG on mRNA. Two tRNAs are now bound (max)
  4. Methionine is bound to Threonine by a peptide bond by peptidyl transferase (from rRNA)
  5. The ribosome moves along mRNA and releases the first tRNA. The second is now the first.
  6. This process repeats, until the ribosome reaches the stop codon and the polypeptide is released.
• Where does mRNA bond when it leaves the nucleus?

  Small subunit of a ribosome at its start codon
• What brings the first amino acid to the mRNA?

  tRNA complementary anticodon
• The first codon is always AUG what will the first amino acid be?

  methionine
• How does the tRNA know the correct amino acid to bring?

  complementary anticodon
• What codes for the second amino acid?

  The next codon (3 bases) codes for the next amino acid.

  The methionine is bonded to the second amino acid
• DNA - Stores genetic information in a cell
• mRNA - Carries the information for a protein out of the nucleus
• tRNA - Carries the correct amino acids to the ribosomes to make the protein
• rRNA - Makes up part of the ribosomes used to make proteins