DNA and Protein Synthesis

• Define Genome

  The complete set of genes in a cell (including those in mitochondria and/or chloroplasts)
• Define Proteome

  The full range of proteins that a cell can produce (coded for by the cells DNA/genome)
• What is transcription?

  Production of messenger RNA (mRNA) from DNA, in the nucleus
• What is translation?

  Production of polypeptides from the sequence of codons carried by mRNA, at ribosomes
• Similarities of mRNA and tRNA

  • Both are a single polynucleotide strand
• Differences of mRNA and tRNA

  • tRNA is folded into a clover shape whereas mRNA is linear/straight
  • tRNA has hydrogen bonds between paired bases, mRNA doesn't
  • tRNA is a shorter fixed length whereas mRNA is a longer, variable length (more nucleotides)
  • tRNA has anticodons, mRNA has codons
  • tRNA has an amino acid binding site. mRNA does not
• Describe the process of Transcription

  1. RNA polymerase attaches to the start of a gene. H-bonds between the 2 DNA strands break and the strands separate. One strand is used as a template strand for mRNA
  2. Complementary base pairing of free RNA nucleotides along the template strand
  3. RNA polymerase joins adjacent RNA nucleotides
  4. This forms phosphodiester bonds via condensation reactions
  5. Pre-mRNA is formed and this is spliced to remove introns, forming mature mRNA
• Describe the process of Translation

  1. mRNA attaches to a ribosome and the ribosome moves to a start codon (AUG)
  2. tRNA brings a specific amino acid
  3. tRNA anticodon binds to complementary mRNA codon
  4. Ribosome moves along to the next codon and another tRNA binds binds so 2 amino acids can be joined by a condensation reaction forming a peptide bond - using energy from hydrolysis of ATP
  5. tRNA released after amino acid joined polypeptide
  6. Ribosome moves along mRNA to form the polypeptide, until a stop codon is reached
• Describe how the production of mRNA in a eukaryotic cell is different from the production of mRNA in a prokaryotic cell

  • Pre-mRNA is produced in eukaryotic cells whereas mRNA is produced directly in prokaryotic cells
  • Because genes in prokaryotic cells don't contain introns so no splicing in eukaryotic
• Describe the role of ATP in translation

  • Hydrolysis of ATP -> ADP + Pi releases energy
  • So amino acids join to tRNA and peptide bonds form between amino acids
• Describe the role of tRNA in translation

  • Attaches to and transports a specific amino acid in relation to its anticodon
  • tRNA anticodon complementary base pairs to mRNA codon, forming hydrogen bonds
  • 2 tRNA bring amino acids together so peptide bonds can form
• Describe the role of Ribosomes in translation

  • mRNA binds to ribosome with space for 2 codons
  • Allows tRNA with anticodon to bind
  • Catalyses formation of peptide bond between amino acids (held by tRNA molecules)
  • Moves along (mRNA to next codon)