Download E. coli

Introduction to
Molecular Biology
Fundamental Molecular Biology
Historical Background
Classical Experiments
Structure of nucleotides & DNA
What is Molecular Biology?
Study of biological events at a molecular level
The study of genes and gene activity at the molecular level
DNA History
Discovered in 1869 by Friedrich Miescher as a component
of nuclein
By late 19th C. DNA & RNA are known to be polymers
The function of these nucleic acids was not known
Early 20th C. Mendel’s genetics were rediscovered
The concept of a ‘gene’ entered biology
The question was “What makes up genes?”
Three possibilities: DNA, RNA, or Proteins
Three sets of researchers provided the data that once and
for all settled the question
1928: Fredrick Griffith experimented on transformation
1944: Oswald Avery, Colin MacLeod, & Maclyn McCarty
repeated Griffith’s experiments, but added further
biochemical tests
1952: A.D. Hershey & Martha Chase performed their
experiment with bacteriophage
Griffith’s Transformation Experiment
Avery et al. repeated the experiment, but looked at each
class of molecules to see their potential to transform
Hershey – Chase Experiment
Erwin Chargaff’s Data
Allison, Fundamental Molecular Biology
Chargaff’s Rules
How is information encoded within DNA
Erwin Chargaff found that: [purine] = [pyrimidine]
[Adenine] = [Thymidine]
[Cytosine] = [Guanine]
DNA Structure
DNA X-Ray Diffraction Pattern
Created By Rosiland Franklin
Karp, Cell& Molecular Biology, 3E
Watson & Crick Model of DNA Double Helix
http://salmon.psy.plym.ac.uk/year3/PSY339EvolutionaryPsychologyroots/watson-crick-dna.jpg
How does a helix of uniform
pattern store information?
Nucleotide Structure
Sugars
Nitrogenous Bases
Phosphates
Glycosidic Bond
Base + Sugar = NUCLEOSIDE
Base + Sugar + Phosphate = NUCLEOTIDE
Essential Cell Biology, 2/e
Phosphodiester Linkage
Allison, Fundamental Molecular Biology
DNA Structure
Watson-Crick Model of DNA
Two chains of nucleotides form a right-handed helix
Chains run in opposite directions
Sugar-phosphate backbone is on the outside of the chains
The paired bases are in planes nearly perpendicular to the
long axis of the molecule (Base Stacking)
Hydrophobic interactions/Van Der Waal forces stabilize
The two strands are held together by hydrogen bonds
1.09 nm
0.34 nm
0.27 nm
0.6 nm
0.34 nm
Allison, Fundamental Molecular Biology
Allison, Fundamental Molecular Biology
2.0 nm
3.4 nm
0.34 nm
-6° Tilt
34.3° Twist
http://www.web.virginia.edu/Heidi/chapter12/chp12.htm
3 Forms of DNA
2.4nm per turn
3.4nm per turn
11bp per turn
10.5bp per turn
4.6nm per turn
12bp per turn
http://members.tripod.com/arnold_dion/RecDNA/Fig1-2.gif
http://chemistry.umeche.maine.edu/CHY431/Nucleic5.html
If the DNA is wound so that there are fewer bases per
turn <9 bp, it is overwound creating positive supercoiling
The angle of twist increases from 34.3° to 37.7°
If there are more bases per turn >11 bp, it is underwound
creating negative supercoiling
The angle of twist decreases from 34.3° to 30.9°
30.9°<
>37.7°
34.3°
Essential Cell Biology, 2/e
E. coli genome negatively supercoiled
http://www.cbs.dtu.dk/staff/dave/roanoke/genetics980213a.html
11.1Å
10.8Å
Allison, Fundamental Molecular Biology