Chapter 4

• From DNA to RNA to protein

  1. Genes in DNA contain information to make proteins

  2. Cell makes mRNA copies of genes that are needed

  3. mRNA is read at the ribosomes in the rough ER

  4. Protein is produced

  
• mRNA

  Carries the information from a gene in DNA

  
• Ribosomes

  Made of rRNA, consist of subunits and carry out an enzyme-like role

  
• tRNA

  Carries specific amino acids to the ribosome

  
• Transcription

  1. RNA polymerase makes mRNA copies of genes

  2. DNA unzips at the site of the gene that is needed

  3. RNA polymerase matches bases in the sense strand with RNA bases, building a strand of mRNA that carries the information encoded in the DNA

  4. Encoded in DNA is a signal telling RNA polymerase where to stop

  5. Transcription ends at that point

  6. Completed mRNA molecule then moves from the nucleus to the rough ER for translation

  
• Translation


  1. Initiation begins with a tRNA bearing methionine (met) attaching to one of the ribosomal units

  2. Ribosomal unit binds to mRNA where the code for met is located (AUG)

  3. Larger ribosomal subunit now binds to the smaller unit, forming a ribosomal complex

  4. Second codon in mRNA (GUU) matches the anticodon of a tRNA carrying the amino acid valine (CAA)

  5. Catalytic site on the larger subunit binds the two amino acids together using dehydration synthesis, forming a peptide bond between them

  6. Process continues until the ribosome finds a "stop" codon

  7. Subunits detach from one another, the mRNA is released, and the polypeptide chain moves down the ER for further processing

  
• Transcription Animation: units/basics/transcribe
• Mutation

  Any mistakes in the DNA code can result in a "broken" (non-functional) protein

  
• A mutation affecting only a few somatic cells (body cells) might not have any effect, unless the mutation turns the cell cancerous
• A mutation affecting a sex cell can be passed on to the offspring
• Types of Mutations

  • Point mutation: base substitution that may or may not code for a different amino acid
  • Insertion mutation: one or more bases is inserted into the DNA strand
  • Deletion: one or more bases is deleted from the DNA strand

  
• Effects of mutations

  • Original: THE FAT CAT SAT
  • Point mutation: THA FAT CAT SAT
  • Insertion: THE FTT ATC ATS AT
  • Deletion: THE FTC ATS AT
• CTC

  Hydrophilic
• GAG

  None
• CTT

  Hydrophilic
• GAA

  None
• GTC

  Hydrophilic
• CAG

  None
• CAC

  Hydrophobic
• GUG

  Sickle Cell Anemia