DNA: Deoxyribose Nucleic Acid

The Genetic Material

Lecture #22A

Ms. Day Honors Biology

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

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

new from the nuclei of eukaryotic cells

• Later called DNA!!!

Searching for Genetic Material• Fredrick Griffith (1928):

– Studied effects of virulent (virus-causing) bacteria vs. nonvirulent bacteria injected into mice• He 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 •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!!!• He heated smooth (harmful) cells

– So cells were DEAD!– Then he mixed them with living Rough

(benign) cells and injected into mice, BUT 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

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)

So…DNA is the transforming

agent!!

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’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

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

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

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 IS 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

DNA’s Structure

Lecture #22BMs. Gaynor

Honors Biology

DNA and Its Structure (Part 2)

•From 1953

Recall…•DNA and RNA are nucleic acids

•An important macromolecule in organisms that stores and carries genetic information

What is the Double Helix?

•Shape of DNA•Looks like a twisted ladder

•2 coils are twisted around each other

•Double means 2•Helix means coil

The Structure of DNA • Made out of nucleotides

•MONOMERS of nucleic acids•Includes:

•phosphate group (PO4-3)

• nitrogenous base and •5-carbon pentose sugar

1 “link” or

monomer in a DNA

chain

2 Polynucleotides

• MANY nucleotides (“links”) bonded togetherDNA has a

overall negative

charge b/c of the PO4

-3 (phosphate

group)

The Structure of DNA Backbone = alternating PO4

-3 & sugar

•Held together by COVALENT bonds (strong)•Inside of DNA molecule = nitrogen base pairs

•Held together by HYDROGEN bonds (weaker)

Backbone

• Phosphodiester Bond

–The covalent that holds together the backbone

–Found between PO4-3

& deoxyribose sugar of 2 DIFFERENT nucleotides

–STRONG!!!

DNA is antiparallel• Antiparallel means that the

1st strand runs in a 5’ 3’ direction and the 2nd 3’ 5’ direction – THEY RUN IN OPPOSITE

or ANTIPARALLEL DIRECTIONS

• P end is 5’ end (think: “fa” sound)

• -OH on deoxyribose sugar is 3’ end– 5’ and 3’ refers to the carbon

# on the pentose sugar that P or OH is attached to

DNA in Cells• 2 broad categories of cells1. Eukaryotic cells: have nucleus

with DNA– DNA is contained in

structure called a chromosome

– Chromosomes are a LINEAR (line) shape with ENDS called telomeres (protective “caps”)

2. Prokaryotic cells: no nucleus (nucleoid region instead) which contains DNA– DNA is a CIRCULAR shaped

chromosome without ENDS (no telomeres)

DNA Bonding• Purines (small word, big base)

– Adenine– Guanine

• Pyrimidines– (big word, small base)

– Cytosine

– Thymine

• Chargaff’s rules– A=T, C=G– Hydrogen BondsHydrogen Bonds attractions between the

stacked pairs; WEAK bonds

Why Does a Purine Always Bind with A Pyrimidine?

DNA Double Helix• http://www.sumanasinc.com/webcontent/animations/content/DNA_structure.html• Watson & Crick said that…

– strands are complementary– nucleotides line up on template according to base pair rules (Chargaff’s rules)

• A to T and C to G

•LET’S PRACTICE…Template: 5’ AATCGCTATAC3’

Complementary strand: 3’ TTAGCGATATG5’