LESSON 3

• DNA is the genetic material of the body
• FRIEDRICH MIESCHER (1871):

  • Described DNA when he isolated nuclei from white blood cells in pus on soiled bandages
  • Discovered an acidic substance containing nitrogen and phosphorus in the nuclei, named NUCLEIN, later called NUCLEIC ACID
• ARCHIBALD GARROD (1902):

  • Linked inherited disease and protein
  • Noted that people with certain inborn errors of metabolism did not have certain enzymes
• FREDERICK GRIFFITH (1928):

  • Identified DNA as the genetic material through experiments with Streptococcus pneumoniae bacteria
  • Experiment 1 (Type R Bacteria): Rough texture, mouse immune system recognizes and kills them
  • Experiment 2 (Type S Bacteria): Smooth texture due to capsule, mouse immune system can't recognize and kills them
  • Experiment 3 (Heated Type S): Control experiment, heating killed bacteria preventing pneumonia
  • Experiment 4 (Heated Type S + Type R): Mixture caused pneumonia due to transformation of DNA
• OSWALD AVERY, COLIN MACLEOD, MACLYN MCCARTY (1944):

  • Hypothesized DNA as Griffith's "transforming principle"
  • Treatment with deoxyribonuclease disrupted transformation, confirming DNA as genetic material
• ALFRED AND MARTHA CHASE (1953):

  • Radioactive experiments showed DNA, not protein, as the genetic material
• ERWIN CHARGAF (1950s):

  • Showed DNA contains equal amounts of adenine-thymine and guanine-cytosine bases
• MAURICE WILKINS AND ROSALIND FRANKLIN:

  • Used X-ray diffraction to reveal DNA's helix structure
  • Franklin distinguished "A" and "B" forms of DNA
  • Watson and Crick discovered the double helix structure
• WATSON AND CRICK:

  • Discovered DNA's double helix structure using cardboard cutouts
  • Built the Ball and Stick Model
  • Received the Nobel Prize
• DNA STRUCTURE:

  • Gene specifies amino acid sequence in a protein
  • Nucleotide consists of deoxyribose sugar, phosphate group, and nitrogenous base
  • Purines (Adenine, Guanine) have a two-ring structure
  • Pyrimidines (Cytosine, Thymine) have a single-ring structure
  • DNA sequences measured in base pairs (Kilobase and Megabase)
• POLYNUCLEOTIDE CHAINS ARE ANTIPARALLEL:

  • Phosphodiester bonds hold sugar and phosphates together
  • Polynucleotide chains create a continuous backbone
  • Antiparallelism works by moving clockwise, 5' to 3' and 3' to 5'
• COMPLEMENTARY BASE PAIRING:

  • Specific purine-pyrimidine couples
  • Hydrogen bonds hold base pairs together
  • Two hydrogen bonds join A and T, three hydrogen bonds join G and C
• DNA CONFIGURATION IN THE NUCLEUS:

  • Length of stretched-out DNA of the smallest human
• DNA Configuration in the Nucleus
• Stretched out DNA of the smallest human chromosome is 14 millimeters (thousands of a meter)
• During cell division, DNA shrinks inside a nucleus by a factor of 7,000
• Proteins that compress the DNA
• Scaffold proteins form frameworks that guide DNA strands
• Histones are where DNA coils around, forming structures that resemble beads on a string
• Nucleosome is a DNA bead, a unit of chromatin structure consisting of DNA coiled around an octet of histone proteins
• Characteristics of DNA
• DNA wraps at several levels until it is compacted into a chromatid
• A nucleosome is composed of eight histone proteins (a pair of each of four types) plus the 147 nucleotides of DNA entwined around them
• A fifth type of histone protein anchors nucleosomes to short "linker" regions of DNA
• The linkers tighten the nucleosomes into fibers 30 nanometers (nm) in diameter
• Only small sections of the DNA double helix are exposed
• Chromatin
• Chromatin is chromosome substance, colored materials
• It consists of 30% histone proteins, 30% scaffold proteins and other proteins that bind DNA, 30% DNA, and 10% RNA
• CTCF is an anchor protein that brings together parts of the DNA sequence within the same long DNA molecule to form the overall "loop-ome" structure
• Discovering the Structure of DNA
• Phoebus Levene identified the 5-carbon sugars ribose and deoxyribose, revealing the chemical distinction between RNA and DNA
• Erwin Chargaff analyzed the base composition of DNA from various species and observed regular relationships
• Rosalind Franklin and Maurice Wilkins used x-ray techniques
• James Watson and Francis Crick deciphered the structure of DNA, forming a double helix
• DNA Structure
• A gene is a section of a DNA molecule, with the order of bases specifying the amino acid sequence in a protein
• A nucleotide is composed of a deoxyribose sugar, a phosphate group, and a nitrogenous base
• Purines (Guanine and Adenine) are composed of a two-ring nitrogenous base structure
• Pyrimidines (Cytosine and Thymine) are composed of a one-ring nitrogenous base structure