DNA to Proteins pt1

• Gene


  A basic unit of heredity composed of a sequence of nucleotides in DNA that encodes the synthesis of RNA and generally induces the production of a polypeptide (protein)
• Transcription unit


  The DNA region where transcription occurs from the DNA template strand to synthesize an RNA transcript in the 5' to 3' direction, running between the initiation and termination sites
• Neurospora crassa (bread mold)

  • Grown in minimal medium to determine if it can synthesize all necessary biological molecules
  • Exposed to X-ray to induce DNA mutation

  
• Tatum and Beadle experiment on bread mold

  1. Grow fungus in minimal medium

  2. If fungus cannot grow, supplement with intermediates of biochemical pathway to identify mutated enzyme

  3. Conclude that a gene encodes the structure of one enzyme protein
• One-gene / one polypeptide hypothesis

  A specific stretch of DNA, the gene, encodes for the structure of one enzyme protein
• Today, the relationship is generalized to the one-gene / one polypeptide hypothesis because many enzymes contain multiple polypeptide subunits, each encoded by a separate gene
• Central Dogma


  Information passes in one direction, from the gene (DNA) it is transcribed to m-RNA, and translated to amino acids (polypeptide/protein)

  
• Retrovirus are RNA viruses that can reverse the central dogma direction
• One gene / one enzyme hypothesis


  The discovery that one gene encodes one enzyme protein
• Tatum and Beadle experiment

  • Experiment on bread mold
• DNA to proteins


  1. DNA transcribed to mRNA

  2. mRNA translated to amino acids (protein)

  
• Many enzymes contain multiple polypeptide subunits (quaternary structure), each encoded by a separate gene
• One-gene / one-polypeptide hypothesis

  Generalized relationship between genes and polypeptides
• Central Dogma


  Information passes in one direction, from gene (DNA) to mRNA to protein
• Retrovirus are RNA base virus that use reverse transcription to insert their own code into the host genome during infection
• Transcription


  1. Template strand of DNA transcribed to single-strand mRNA molecule

  2. Coding strand of DNA has same sequence as mRNA (but T are U)

  3. mRNA transcript used to direct synthesis of polypeptides
• Prokaryotic transcription


  • Single RNA polymerase
  • Requires promoter, start site, termination, stop site
• Prokaryotic transcription steps


  1. Initiation

  2. Elongation

  3. Termination
• Initiation


  • σ factor joins core polymerase to form holoenzyme
  • σ factor recognizes promoter sequences
  • Helix opens at -10 base pair, transcription begins at +1 start site
  • σ factor dissociates (or stays weakly bound)
• Promoter


  Region upstream of start site where σ factor binds at -35 and -10 base pairs
• Elongation


  1. Transcription bubble forms as RNA is elongated 5' to 3'

  2. Newly transcribed DNA rewound behind bubble
• Termination


  1. Rho-dependent: Rho factor binds mRNA, climbs to polymerase and pulls apart transcript

  2. Rho-independent: Hairpin and U-rich region cause polymerase to stall

  
• Prokaryotes can do transcription and translation at the same time as they lack a nucleus
• Explain the Beadle and Tatum?

  They used a fungus called Neurospora crass, which is a bread mold, to figure out the relationship between genes and enzymes. They first put the mold in a minimal medium and put X-rays to induce mutation of the mold. Then, they supplemented the fungus with intermediates and they identified which gene gave which enzyme. They then came up with the conclusion that one gene codes for one polypeptide.
• What is the central dogma?

  The central dogma represents the flow of information. It starts from the DNA and then the information will be transcribed by m-RNA and, finally, it will be translated into amino acids by the t-RNA.
• What does a retrovirus do?

  It use an enzyme called revere transcriptase to insert down its own code to the DNA. Basically, it just does the opposite of the m-RNA.