DNA and protein synthesis

• Genome

  The complete set of genes in a cell
• Proteome

  The full range of proteins that a cell is able to produce
• Function of mRNA

  Transfers genetic information from the DNA to ribosomes, where it acts as a template for protein synthesis.
• Structure of mRNA

  • Very long (shorter than DNA though) , single polynucleotide chain
  • Polymer of RNA nucleotides
  • Every three bases make up a codon- the sequence of codons determines the amino acid sequence of a specific polypeptide that will be made.
• Function of tRNA

  Transfers amino acids that are used to make proteins to ribosomes
• Structure of tRNA

  • Shorter, single polynucleotide chain
  • Hydrogen bonds between specific base pairs -> tRNa molecule folds into a cloverleaf shape
  • One end= specific sequence of three bases (anticodon)
  • Other end= amino acid binding site
• tRNA molecule

  A) Amino acid binding site

  B) Anticodon

  
• What provides the energy for the bond to form between the amino acid and the tRNA molecule?

  ATP
• What are the two stages of protein synthesis?

  1. Transcription
  2. Translation
• Where does transcription occur in eukaryotic and prokaryotic cells?

  • Eukaryotic= nucleus
  • Prokaryotic= cytoplasm
• Outline the process of transcription

  1. DNA helicase breaks the hydrogen bonds between complementary bases and unwinds the DNA, exposing some bases.
  2. Free RNA nucleotides associate with their exposed complementary bases of the template DNA strand.
  3. RNA polymerase adds each nucleotide to the mRNA polynucleotide chain by forming a phosphodiester bond.
  4. Hydrogen bonds reform between complementary bases of DNA and the strand recoils into a double helix.
  5. When RNA polymerase reaches a stop triplet code, it detaches from DNA and production of the mRNA is complete.
• What does transcription produce in transcription?

  pre-mRNA, which must be spliced out by a spliceosome to remove the introns.
• Outline the process of translation.

  1. A ribosome attaches to the start codon at one end of the mRNA.
  2. A tRNA molecule with an anticodon complementary to the first codon on the mRNA molecule attaches itself to the mRNA by complementary base pairing.
  3. A second tRNA molecule attaches itself to the next codon in the same way.
  4. The tRNA molecules bring amino acids with them, which join together by a peptide bond using an enzyme and ATP.
  5. The ribosome moves along the mRNA and the next tRNA molecule binds. The first tRNA molecule dissociates.
  6. The process is repeated and amino acids are added to form a polypeptide chain.
  7. When the ribosome reaches a stop codon, the ribosome detaches.