From Gene to protein

• What are inborn errors of metabolism?


  Diseases where the patient is unable to carry out a particular biochemical reaction
• who discovered inborn errors of metabolism?

  Archibald Garrod, first to connect inherited human disorderw ith Mendels laws of inheritance
• what is Archibold Garrod study?


  Alkaptonuria
• what is alkaptonuria?

  Urine darkens from yellow to brown after its exposure to the air.

  Urine contains a large amount of homogentisic acod
• Is alkaptonuria dominant or recessive?

  Recessive
• What was Archibold Garrods theory?

  Patients with Alkaptonuria lack the enzyme for breaking down homogentisic acid, this lack of the enzyme is due to a defect in a gene
• what enzyme is required for breaking down Alkaptonuria?

  homogentisic acid oxidase
• What were Beadle and Tatums experiments?

  one gene, one enzyme
• What did Beadle and Tatum use as their model organism?

  Neurospora crassa (Bread mould)
• Why was neurospora chosen?

  They are a genetically simple model organism.

  They have a haploid stage of life cycle (so recessive traits will appear in offspring), diploid usually requires crossing of two generations
• Why can wild type neurospora grow without many nutrient?

  It has enzyme to generate its own amino acids
• How did Beadle and Tatum test if neurospora lacked an enzyme?

  If it lacked the gene it would be unable to grow without particular nutrient so if placed in a medium that lacked that nutrient it would die
• how did Beadle and Tatum test if genes were responsible for specific chemical reactions?

  they irradiated Neurospora with X-rays
• what are auxotrophic mutants?

  Auxotrophs are mutant strains that cannot synthesize a particular molecule require for growth
• How to screen for auxotrophic mutants?

  1. culture individual sproes on complete medium
  2. Transfer to minimal medium to identify possible auxotrophs
  3. Test candidates for growth on minimal medium supplemented with different classes of nutrients
  4. test candidates for growth on minimual mediums supplemted with individual amino acids
  5. identify the amino acids that allows your mutant to grow
• who identified the three classes of arginine auxotroph?

  Srb and Horowitz
• what is a class I arginine auxotroph?

  MM + ornithine

  MM + citrulline

  MM + arginine
• What is a class II arginine auxotroph?

  MM + citrullin

  MM + arginine
• what is a class III arginine auxtroph?

  MM + arginine
• where do class I arginine auxtroph have their mutation?

  in Enzyme A which converts precursor into ornithine
• Where do class II arginine auxotroph have their mutation?

  In enzyme B between ornithine and citrulline
• where doe class III arginine auxotrophs have their mutation?

  In enzyme C which converts citrulline to arginine
• Who proposed the One gene one enzyme hypothesis?

  Beadle and Tatum
• what is the one gene one protein hypothesis?

  not all genes products are enzymes
• what is the one gene - one polypeptide hypothesis?


  Some proteins are made of more than one polypeptide chain
• How do genes specify proteins?

  DNA in nucleus but proteins made in cytoplasm.

  Genes do not specify proteins directly

  Messenger required - information transferred from nucleus to cytoplasm

  messenger is ribose nucleic acid
• What is the structure of RNA?

  RNA: a polymer of nucleotides containing ribose sugar and combinations of four bases: adenine, guanine, cytosine and uracil – usually single-stranded
• what is the pulse-chase experiments?

  Technique to study protein movement. Radioactive uracil in the nucleus moved into cytoplasm, suggesting RNA is made in the nucleus and moves into cytoplasm
• What are the 2 steps in gene express?

  transcription and translation
• what is a central dogma?

  DNA replication, transcription, translation.
• what is transcription catalysed by?

  RNA polymerase
• do RNA polymerase require a primer?

  No
• Describe the stages of transcription?

  Initiation, elongation, termination
• Describe transcription elongation

  RNA polymerase moves along the DNA template, unwinding the double helix and catalysing the addition of ribonucleotides to the 3' end of the growing RNA molecule
• Describe transcription termination

  terminatiin signal in the newly produced RNA (terminator)
• why is DNA translated?

  to give the 20 letter language of the protein
• how many bases code for the amino acids?

  3
• what was the first code to be proved?

  phenylalaine (UUU, UUC)
• what are the stop codons?

  UAA, UAG, UGA and AUG
• how is the genetic code specific and redundant?

  Specific: each codon can only spcifiy one amino acid

  Redundant: more than one codon code for a specific amino acid