Genetics

• DNA polymerase I replaces the RNA primers with DNA nucleotides where 2 Okazaki fragments meet.
• Ligase joins the Okazaki fragments.
• Scientists Meischer Collected pus & named it nuclein b/c found in nucleus.
• DNA Gri  ith R-strain → no virus S-strain → virus Heat killed s-strain → no virus Heat killed s-strain + r-stain → virus
• Discovered transformation.
• Avery, McLeod & McCarty Stated that DNA was transforming principle.
• Heated s-strain then molecules that were extracted from bacteria were treated with 1 of 3 enzymes to destroy the 3 possible transforming substances then mixed each extract with r-strain bacteria.
• Transcription Step 1: Initiation RNA polymerase binds to DNA (before gene) & starts making complementary copy.
• RNA polymerase binds at a specialized sequence (prometer) on 1 strand of DNA above the start of gene.
• DNA splits at site of RNA polymerase & starts to unravel RNA polymerase a aches matching bases to form a new RNA strand from DNA.
• RNA is made in the 5' → 3' direction, using the 3' → 5' DNA as the template.
• Once RNA polymerase reaches termination site the copying stops RNA polymerase leaves DNA & RNA strand is released DNA rewinds into double helix.
• Post-transcription A  er 3 steps the new transcribed RNA is pre-mRNA & can only leave cell until modified.
• Modifications include the addition of 50 - 250 adenine nucleotides to the 3' end by an enzyme → poly-A polymerase.
• A 5' cap of 7 guanines is added to the start of a pre-mRNA molecule.
• Ribosomes recognize this site & use it as site of initial a  achment.
• Introns (non-coding, intervening sequences of DNA) are removed by enzyme-protein complex → spliclosome and exons (protein coding regions of DNA) are connected.
• Alternative splicing allows us to understand why humans with only about 20000 genes can produce approximately 100000 proteins.
• Alternative splicing enables us to produce different mRNAs from a single DNA gene sequence.
• Protein A and Protein B are different mRNAs from a single DNA gene sequence.
• First Step of Transcription: RNA polymerase binds to DNA and starts making complementary copy
• What is the prometer?

  Specialized sequence on 1 strand of DNA above the start of gene
• Second step of transcription: DNA splits at site of RNA polymerase and starts to unravel. RNA polymerase attaches matching bases to form a new RNA strand from DNA.
• Third step of transcription: Once RNA polymerase reaches termination site the copying stops. RNA polymerase leaves DNA and RNA strand is released. DNA rewinds into double helix.
• Poly A modification: Addition of 5-250 adenine nucleotides to the 3' end by an enzyme - Poly-A polymerase. Chain of adenine nucleotides (ploy(a) tail) protect the mRNA from attach by RNA-digesting enzymes in the cytosol
• Guanine modification: 5' cap of 7 guanines added to the start of a pre-mRNA molecule. Ribosomes recognize this site and use it as site of initial attachment
• Splicing modification: Introns (non-coding, intervening sequences of DNA) are removed by splisosome and exons (protein coding regions of DNA) are connected.
• translation step 1:

  begins when the small ribosomal subunit binds to the mRNA and a charged tRNA binds to the start codon (AUG) on the mRNA
• tRNA carries methionine
• 1st tRNA carrying Met will to go p site all others go to a site first
• translation step 2:

  1. Codon Recognition: the appropriate anticodon of the next tRNA goes to a site.
  2. Peptide bond formation: peptide bonds are formed that transfer the polypeptide to the a site tRNA
  3. Translocation: the tRNA in the a site moves to the p site, the tRNA is the p site goes to the E site. The a site is open for the next tRNA.
• translation step 3:


  occurs when a stop codon in the mRNA reaches the a site
• stop codons signal for a release factor

  • hydrolyze the bond that holds the polypeptide to p site
  • the polypeptide is released
  • all translational units disassemble
• As translation takes place, the growing polypeptide chain begins to coil and fold
• Genes determine the primary structure and primary structure determines final shape
• Retrovirus are the exception to the standard flow of genetic info as info goes from RNA to DNA. They use and enzyme called reverse transcriptase. DNA becomes part of RNA.
• Epigenetics is a mechanism for regulating gene activity independent of DNA sequence that determines which genes are turned off/on:

  • in a particular cell
  • different disease state
  • response to physiological stimulus
• Lac Operon in E.coli

  • Control Region: respond to the presence/absence of lactose and glucose
  • Genes: produce enzymes necessary for digesting lactose
• What are the enzymes in Lac operon E.coli?

  • B galactosidase: cleaves lactose into glucose and galactose
  • Permease: Transports lactose across membrane into cell
  • Transacetylase: adds acetyl group to lactose
• If there are no proteins bound to either the activator/operator, RNAP is free to bind to the promoter and transcribe the genes.