DNA and Protein Synthesis
What is DNA?
• Contains the genetic
information for making all the proteins in the
cell
In the Beginning…..• The world of science debated on what the
genetic material was• Some thought it was protein• Others believed it was DNA
Evidence for a Genetic “Factor”• 1928 – Frederick Griffith’s “Transforming
Factor” Experiment
• Conclusion: “Something” from Heat-treated Strain 1 “transformed” Strain 2 to become deadly
DNA is Proven to be that Genetic Factor
• 1944 – Oswald Avery and colleagues focused on two of the genetic factor candidates: protein and DNA
• Repeated Griffith’s experiment, but with a modification
Proteases
DNases
Mouse dies
Mouse livesConclusion – DNA is the transforming, thus genetic material
Avery Questioned In the Scientific Community
Final Proof that DNA is the Genetic Material
• 1952 – Hershey-Chase Experiment• Virus = DNA (inside) + protein (outside)
Conclusion: DNA was the genetic material due to viruses passing on DNA for reproduction
The DNA “Twist”• DNA is a double helix• Every 10 nucleotides
there is a 360 degree rotation
• The structure of DNA is accredited to James Watson, Francis Crick and Rosalind Franklin
Frame of Reference
Where is the DNA located in eukaryotes? Prokaryotes?
The Structure of DNA• DNA = deoxyribonucleic acid
• DNA is a polymer built up from monomers
• Monomers are called nucleotides
The Structure of DNA Continued
• Phosphate Group – provides the “backbone” of DNA 5’ end (5 prime end)
• Sugar – called a deoxyribose; also part of the DNA “backbone” 3’ end (3 prime end)
• Backbone of DNA called the sugar-phosphate backbone
Nitrogenous Bases of DNA• Nitrogenous bases of
DNA– Two Types– Pyrimidines
Thymine (T) and Cytosine (C)
– Purines Adenine (A) and Guanine (G)
– Purines are double ringed, pyrimidines are single ringed
Pairing of Bases
• In DNA G hydrogen bonds with C • T hydrogen bonds with A
C G G T A C A T G C A T A
G C C A T G T A C G T A T
Chargaff’s Rule• 1950 – Erwin Chargaff discovered:
– A approximately equals T– G approximately equals C
• This is true for all species!• In humans
– A = 30.9% and T = 29.4%– G = 19.9% and C = 19.8%
Let’s Put the Structure Together• Notice the following:
– 5’ and 3’ ends– A:T and G:C– Hydrogen bond
numbers– Sugar-phosphate
backbone– Two strands are
antiparallel