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 HistoryDiscovered 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

Allison, Fundamental Molecular Biology

Erwin Chargaff’s Data

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

http://salmon.psy.plym.ac.uk/year3/PSY339EvolutionaryPsychologyroots/watson-crick-dna.jpg

Watson & Crick Model of DNA Double Helix

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 DNATwo 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

Allison, Fundamental Molecular Biology

1.09 nm

0.6 nm

0.34 nm

0.34 nm

0.27 nm

Allison, Fundamental Molecular Biology

-6° Tilt

34.3° Twist

http://www.web.virginia.edu/Heidi/chapter12/chp12.htm

2.0 nm

3.4 nm

0.34 nm

http://members.tripod.com/arnold_dion/RecDNA/Fig1-2.gif

2.4nm per turn 3.4nm per turn 4.6nm per turn

11bp per turn 10.5bp per turn12bp per turn

3 Forms of DNA

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°

34.3°

30.9°<

>37.7°

Essential Cell Biology, 2/e

http://www.cbs.dtu.dk/staff/dave/roanoke/genetics980213a.html

E. coli genome negatively supercoiled

Allison, Fundamental Molecular Biology

11.1Å

10.8Å