Dna to proteins pt2

• George Beadle and Edward Tatum experiment


  Showed the one-gene/one-polypeptide relationship in protein synthesis

  
• One-gene/one-polypeptide


  The relationship between a gene and the polypeptide it encodes
• Gene


  A unit of hereditary information
• Transcriptional unit


  A segment of DNA that is transcribed into an RNA molecule

  
• Central Dogma of biology

  DNA -> RNA -> Protein

  
• Reading frame


  The way a sequence of nucleotides in DNA or RNA is grouped into codons

  
• Triplet code


  The genetic code where each amino acid is specified by a sequence of three nucleotides
• Genetic code


  The set of rules by which information encoded in genetic material (DNA or RNA sequences) is translated into proteins

  
• The genetic code is nearly universal across all organisms
• Prokaryotic transcription


  RNA polymerase transcribes DNA template strand to produce mRNA, initiates at promoter, terminates at terminator

  
• Eukaryotic transcription


  RNA polymerase II transcribes DNA template strand to produce mRNA, initiates at promoter, adds 5' cap and 3' poly-A tail

  
• Eukaryotic RNA polymerases


  • RNA polymerase I transcribes rRNA, RNA polymerase II transcribes mRNA, RNA polymerase III transcribes tRNA

  
• Eukaryotic transcription initiation


  Transcription factors bind promoter, recruit RNA polymerase II, form initiation complex

  
• Eukaryotic transcription elongation


  Addition of 5' cap, elongation of mRNA

  
• Eukaryotic transcription termination


  Cleavage of mRNA at specific site, addition of 3' poly-A tail

  
• 5' cap


  Modified guanine nucleotide added to 5' end of eukaryotic mRNA, protects mRNA from degradation and aids translation

  
• 3' poly-A tail


  Sequence of adenine nucleotides added to 3' end of eukaryotic mRNA, protects mRNA from degradation

  
• Eukaryotic mRNA is shorter than the DNA sequence that encodes it
• Exons


  Coding sequences in a gene that are expressed in the final mRNA

  
• Introns


  Non-coding sequences in a gene that are removed during mRNA processing

  
• Eukaryotic pre-mRNA splicing


  Spliceosome complex removes introns and joins exons to form mature mRNA

  
• Eukaryotic genes can undergo alternative splicing to produce multiple mRNA and protein isoforms from a single gene

  
• Exons make up only about 1% of the human genome, introns make up 24%, and the rest is intergenic DNA
• Remnants of ancient viruses make up about 8% of the human genome
• Amino acids


  Monomers that make up proteins
• tRNA


  Transfers amino acids to the ribosome during protein synthesis

  
• Ribosome


  Organelle that translates mRNA into protein

  
• mRNA


  Transcript of a gene that is used as a template for protein synthesis

  
• Exons


  Compose only about 1% of the human genome
• Introns


  Compose about 24% of the human genome
• Intergenic DNA


  Represents the rest of the human genome (75%) and is composed of noncoding DNA. Occasionally some intergenic DNA acts to control nearby genes, but most of it has no currently known function

  
• Remnants of ancient viruses

  Compose about 8% of the human genome. The viral DNA come from retrovirus, which can copy their genome to the host genome during infection
• Retrovirus


  RNA base virus that use reverse transcription to insert their own code into the host genome during infection
• Components needed for translating from m-RNA to a polypeptide protein

  • Amino acids
  • t-RNA
  • Ribosome
  • m-RNA

  
• 1. RNA


  • Brings the amino acids to the ribosome to make proteins
  • Acceptor end binds to the amino acid
  • Anticodon loop contains 3 nucleotides complementary to m-RNA codons

  
• Different t-RNA molecules carry each 20 types of amino acids to the ribosome for incorporation into a polypeptide

  
• Aminoacyl-tRNA synthetases


  • Must be able to recognize specific t-RNA molecules as well as their corresponding amino acids
  • Enzymatic reaction joins an amino acid to a t-RNA, now called a charged t-RNA. An ATP molecule provides energy for this endergonic reaction

  
• Ribosome


  • The organelle that takes the information of the m-RNA and translates it into protein
  • The two functions of the ribosome involve decoding the transcribed message (m-RNA) and forming peptide bonds
  • The formation of peptide bonds requires the enzyme peptidyl transferase (Ribozyme), which resides in the large subunit

  
• Codons


  • Triplets of nucleotides in the m-RNA that the ribosome will read to produce a polypeptide
  • Each codon codes for one amino acid, but each amino acid can be coded for by more than one codon
  • The genetic code is considered to be degenerate

  
• Translation


  Always starts with the codon AUG (methionine) and stops with UGA, UAG or UAA