DNA: Deoxyribose Nucleic Acid

The Genetic Material

Chapter 2:Introduction

to DNA

Ms. Gaynor

Honors Genetics

DNA • Deoxyribose nucleic acid type of nucleic acid

– What is the other type of nucleic acid?

• RNA• DNA function

– to hold genetic code – Genetic code = genetic

instructions to make proteins

• DNA is found in nucleus of eukaryotic cells

• Found in nucleoid region in prokaryotes

The Short History of DNA and Genetics (Part 1)

•From 1866-1953

Searching for Genetic Material• Gregor Mendel

(1866): – discovered that

inherited traits are determined by discrete units, or 'genes,’ - passed on from the parents.

• Freidrich Miescher(1868): – discovered DNA– Isolated something

new from the nuclei of eukaryotic cells

• Later called DNA!!!

Searching for Genetic Material• Thomas Hunt Morgan (1910):

– Worked with fruit flies• Specifically eye color of these flies!

– Discovered genes are located (linked) on chromosomes

Searching for Genetic Material• Fredrick Griffith (1928):

– Studied effects of virulent (virus-causing) bacteria vs. nonvirulent bacteria injected into mice

– Used transformation:• Inserted foreign DNA and

changed protein/ trait

– believed that the transforming agent was an inheritance molecule.

Non-virulent vs. Virulent

Bacteria

SMOOTH:kill

ROUGH: harmless

BAD/HARMFULNOT HARMFUL/BENIGN

Griffith's Transformation Experiment

• Used the Pneumococcus bacteria – Include2 types:

•a virulent S strain with a Smooth coat– kills mice

•a non-virulent R Rough strain – does not kill mice.

• Heat destroys (kills) living cells!!!• When heated Smooth (harmful) cells

(DEAD) are mixed with living Rough (benign) cells and injected into mice, the mouse dies. – WHY?

http://www.quia.com/files/quia/users/hlrbiology/Animations/08_DNA_and_Proteins/Griffith_Mouse_Experiment.swf

Searching for Genetic Material

http://brookings.k12.sd.us/biology/ch12DNARNA/Chapter%2012A.mpg

Searching for Genetic Material

Oswald Avery, Colin MacLeod, & Maclyn McCarty (1944):

• Reported that “transforming agent” in Griffith's experiment was DNA.

• Also used the Pneumococcus bacteria and test tubes (NOT mice)

The Avery, et al. Experiment • Used S (harmful) strain

– Opened up the cells– Isolated

• DNA, proteins and other materials SEPERATELY

– Mixed R bacteria with these different materials– Only those mixed with DNA were transformed

into S bacteria.S DNA

+ R Bacteria

S PROTEINS +

R Bacteria

TEST

TUBES

OTHER S CELL PARTS

(sugar/RNA) +

R Bacteria

http://wps.aw.com/bc_russell_igen_me_1/

Discovering the Structure of DNA

Edwin Chargaff (1950)•Discovered a 1:1 ratio of adenine to thymine and guanine to cytosine in DNA samples from a variety of organisms.

Chargaff's Rule (Data)

Relative Proportions (%) of Bases in DNA

ORGANISM A T G C

Human 30.9 29.4 19.9 19.8

Chicken 28.8 29.2 20.5 21.5

Grasshopper 29.3 29.3 20.5 20.7 

Sea Urchin 32.8 32.1 17.7 17.3

Wheat 27.3 27.1 22.7 22.8

Yeast 31.3 32.9 18.7 17.1

E. coli 24.7 23.6 26.0 25.7

Discovering the structure of DNA

Chargaff movie and Building Blocks movie

http://www.hhmi.org/biointeractive/dna/animations.html

Chargaff’s RulesA = TC = G

Discovering the structure of DNA

Maurice Wilkins (1952)• Photographed DNA using x-

ray crystallography• Worked with another

scientists named Rosalind Franklin

• Awarded the 1962 Nobel Prize for Physiology or Medicine with Watson and Crick

Linus Pauling’s TRIPLE helix

Pauling Triple Helix Model

http://www.hhmi.org/biointeractive/dna/animations.html

Linus Pauling(1954)

• proposed a triple helix structure for DNA

Discovering the structure of DNA

Rosalind Franklin (1952)

•Obtained sharp X-ray diffraction photographs of DNA (Photo 51)•Watson and Crick used her data revealed its helical shape

•Watson and Crick went on to win Nobel Prize (1962) for their DNA model

Photo 51

How did PHOTO 51 reveal DNA’s helical shape?

•  X-rays passing through a helix diffract at angles perpendicular to helix making an "X" pattern, which favors an equal diameter "helix".

She finally gets credit Rosalind Franklin University of Medicine and

Science, located on Green Bay Road in North Chicago, Illinois

Searching for Genetic Material

Alfred Hershey & Martha Chase (1952)– Confirmed DNA was genetic material

– Used bacteriophages (viruses)

– HYPOTHESIZED DNA, not protein, is the hereditary material

Searching for Genetic Material

Hershey and Chase Experiment Animation

http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter14/animations.html

Searching for Genetic MaterialHershey and Chase Experiment

Discovering the structure of DNA James Watson & Francis Crick (1953)

•Discovered double helix structure•Solved the three-dimensional structure of the DNA molecule

Watson Constructing Bair Pairs movie

http://www.hhmi.org/biointeractive/dna/animations.html