2.1.3. Nucleotides and nucleic acid

• The production and secretion of proteins

  1. mRNA leaves the nucleus via the nuclear pores

  2. It is used by the ribosomes on the rough endoplasmic reticulum to construct a protein

  3. The protein travels in a vesicle to the Golgi apparatus

  4. The vesicle is moved by the cytoskeleton, possibly using tiny protein motors that 'walk' along the microtubules using them as a track

  5. The Golgi apparatus modifies the protein (often adding a carbohydrate group) and repackages it into a vesicle

  6. This vesicle is moved to the cell-surface (plasma) membrane

  7. The vesicle fuses with the membrane to release the protein from the cell
• Semi-conservative DNA replication

  1. DNA double helix unwinds and the hydrogen bonds break between complimentary base pairs as DNA helicase unzips it
  2. free nucleotides are are attracted to exposed bases by complementary base pairing (A - T, C - G)
  3. joined together by phosphodiester bonds (negative) by DNA polymerase, forming a sugar-phosphate backbone
  4. one old and one new strand
• in semi-conservative DNA replication

  • original carries N-14 as part of nitrogenous base, allowing it to float in the centrifuge as lighter, new carries N-15 so sinks. thus centrifugation separates these substances of different densities using centrifugal force
  • parent is all n-14, F1 is all n-14/ n-15 mix, second generation half n14/15 and half n-15
• DNA polymerase only works in one direction from 3’ end to 5’ end, meaning the lagging strand has small gaps left in the backbone. DNA ligand works to seal these gaps
• protease breaks down the histone proteins in DNA
• • detergent distrusts the nuclear envelope/ cell membrane and releases its contents. it attracts phospholipids and water molecules by working as an emulsifier
  • salt and ethanol helps DNA shed water/precipitate
• • phospodiester bonds are between adjacent nucleotides which is done by dna polymerase in the backbone. they consist of a phosphate group between the pentose molecules. condensation reaction that water is released with
  • hydrogen bonds are between complementary bases/ antiparallel strands
  • polynucleotides are anti parallel
• • two hydrogen bonds between T and A
  • three between C and G
  • purine only binds with pyrimidine because they are different sizes
• • sense/ coding strand is 5’ to 3’
  • the antisense/ nonsense/ template is 3’ to 5’
• DNA replication and transcription

  similarities

  • DNA unwinds and unzips
  • helicase enzymes
  • template DNA
  • complementary base pairing
  • hydrogen bonds
  • free, activated nucleotides
  • polymerase enzymes

  differences

  • only a small section unzips in t
  • both strands are templates in r
  • different helicase enzymes
  • products; two daughter strands of DNA in r, one mRNA strand in t
  • mRNA leaves nucleus, DNA remains bound to the template strand
  • RNA v DNA polymerase and free nucleotides
• DNA is too large too leave the nuclear envelope so transcription allows for DNA to be copied to mRNA which goes to ribosomes in the RER.