DNA Structure

• Sutton and Boveri


  proposed the chromosome theory of heredity in 1903
• Friedrich Miescher


  described DNA in 1868
• Phoebus A. Levene


  proposed that DNA was composed of a repeating chain of nucleotides found in a 1:1:1:1 ratio
• proteins


  originally believed to be the genetic material due to their variable structure and abundant presence in cells
• Frederick Griffith


  performed experiment on pneumonia cells and found that a heat killed virulent bacteria could transform a non-virulent bacteria into a virulent one, showing evidence of transformation/hereditary exchange
• Avery, MacLeod, and McCarty


  performed experiment that identified the transforming principle from Griffith experiment as DNA
• nucleases


  enzymes that break down phosphodiester bonds
• deoxyribonuclease


  type of nuclease that breaks down DNA
• ribonuclease


  type of nuclease that breaks down RNA
• protease


  breaks down peptide bonds in polypeptide chains (proteins)
• viruses can have single or double stranded RNA as well as single or double stranded DNA genomes
• nucleotide


  basic building block of a nucleic acid containing a phosphate, a pentose sugar, and a nitrogenous base
• purine base


  base with two rings; guanine and adenine
• pyrimidine base


  base with one ring; cytosine, uracil, and thymine
• nucleoside


  a base covalently bonded to a sugar (1'C to N-1 or N-9)
• the addition of a phosphate group to a nucleoside by a phosphoester linkage makes a nucleotide
• nucleotides are named by the type of nucleoside followed by the number of phosphate groups (ex: thymidine diphosphate)
• polynucleotide


  chain of multiple nucleotides joined by linking the 5' phosphate of one to the 3' carbon of the next
• Angstrom 


  unit of measurement equal to $1\times10^{-10}$ m
• Erwin Chargaff


  measured the base composition of DNA and found that the amount of purine nucleotides in a genome equals the amount of pyrimidine nucleotides
• Rosalind Franklin


  used x-ray diffraction to determine that the structure of DNA was helical with stacked bases about 0.34 nm apart
• Watson and Crick


  awarded the Nobel prize for describing DNA structure as a double right-handed helix of polynucleotide chains with a sugar-phosphate backbone facing outward and the bases inward
• the helices of DNA are held together by the hydrogen bonds between bases - A and T have 2 bonds while C and G have 3
• major groove


  large dip in helix created by uneven base stacking, exposes bases and allows attachment of DNA binding proteins
• minor groove


  small dent in helix caused by uneven base stacking, exposes some bases but proteins do not usually bind here
• Central Dogma of Molecular Genetics


  proposed by Crick; says that DNA is transcribed to mRNA in the nucleus then moved to the cytoplasm through the nuclear pore and translated to a protein by a ribosome
• B DNA


  most biologically applicable type of DNA, right-handed with 10 bp/turn
• A DNA


  hybrid between RNA and DNA, right-handed with 11 bp/turn
• Z DNA


  synthetic type of DNA that is left-handed with 12 bp/turn
• RNA


  composed of nucleotides with ribose as the pentose sugar connected from the 5' to 3' end by phosphodiester bonds
• Svedberg coefficient (S)


  a measure of how quickly particles move through a substance when subject to centrifugation
• spectroscopy


  test that characterizes molecules by how they interact with different wavelengths of light
• A260


  a unit used to measure the quantity of nucleic acids through absorbance of light
• denaturation


  the separation of two nucleotide chains in DNA by breaking the hydrogen bonds through heat, addition of destabilizing substance, or removal of stabilizing counterions
• melting profile


  a graph of A260 (Y) versus temperature (X)
• hyperchromic shift


  an increase in UV absorption with increasing temperature due to the breaking of hydrogen bonds
• melting temperature (Tm)


  the midpoint of a substance's increase in absorbance that tells the temperature at which half of the DNA is no longer double stranded
• renaturation


  the reforming of both strands of DNA that occurs when solution is held at a temperature just below the denaturation temperature after it was split
• annealing


  the reassociation of ssDNA to dsDNA
• hybridization


  the annealing of ssDNA or RNA from two different sources