Ch1

• DNA


  A polymer of deoxyribonucleotides found in the nucleus, mitochondria and chloroplast that carries the genetic information
• Nucleotide


  Consists of a phosphate, sugar (deoxyribose), and a base
• Nucleoside


  Sugar + Base
• Nucleotide


  Nucleoside + Phosphate
• Polynucleotide formation


  Bond formed by a dehydration reaction between 5' phosphate of one nucleotide with the 3' hydroxyl of another nucleotide
• Polynucleotides


  • Linear strands of DNA or RNA, almost always have a free 5' phosphate group at one end and a free 3' hydroxyl group at the other
  • Phosphodiester bond
• Primary structure of DNA

  Phosphodiester linkage
• Secondary structure of DNA

  • Two polynucleotide chains wound around each other in a right-handed double helix
  • Diameter of 2nm
  • Antiparallel orientation
  • Sugar-phosphate backbones on the outside, bases oriented toward the central axis
  • Base pairs bonded by hydrogen bonds
  • Base pairs 0.34nm apart, 10 base pairs per turn
  • Major and minor grooves
• Chargaff's rules


  Amount of adenine = amount of thymine, amount of cytosine = amount of guanine, always an equal proportion of purines (A and G) and pyrimidines (C and T)
• 1. DNA, B-DNA, Z-DNA


  Different structural forms of DNA depending on environmental conditions
• Tertiary DNA structure


  • Higher-order folding that allows DNA to be packed into the confined space of the cell
  • Supercoiling - DNA helix subjected to strain by being over wound and under wound
• Chromatin


  DNA complexed to proteins, the material that makes up eukaryotic chromosomes
• Histone proteins


  • H1, H2A, H2B, H3, H4
• Non-histone proteins


  Scaffold proteins, DNA polymerase, heterochromatin proteins
• Chromatin structure


  • Nucleosome - DNA double helix coiled around histone octamer
  • Chromatosome - nucleosome bound to H1 histone
  • Solenoid - 6 nucleosomes forming a 30nm fiber
• Euchromatin vs heterochromatin


  Euchromatin - less condensed, transcriptionally active

  Heterochromatin - more condensed, transcriptionally inactive
• Nuclear structure


  • Nuclear envelope - double membrane surrounding the nucleus

  Nuclear pores - allow import of proteins and export of RNA/proteins
• Molecular transportation


  Nuclear localization signals (NLS) direct importin proteins to bring in macromolecules like RNA polymerase and histones

  Nuclear export signals (NES) direct exportin proteins to export macromolecules like RNA and ribosomes

  RAN protein exists in GTP and GDP forms, regulating transport
• A gene is a segment of DNA that codes for a specific protein or RNA molecule.
• The Central Dogma describes how genetic information flows from DNA to mRNA to protein.