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