DNA: Deoxyribose Nucleic AcidThe Genetic Material

Introduction to DNA (PART 1)

Ms. Kim Honors Biology

What does DNA stand for?

• Deoxyribonucleic acid

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

information/instructions for making proteins

• DNA is found in nucleus of eukaryotic cells

• Found in nucleoid region in prokaryotes

What is DNA made of?

• DNA is a macromolecule– Made up of nucleotides– Covalently and hydrogen bonded together

• Double stranded– Helix– “Spiral”

What is a nucleotide?

• Molecule made of– Deoxyribose sugar– A phosphate group– A nitrogenous base

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.

• Thomas Hunt Morgan (1910): – 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.

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 the harmfulness of S strain• When heated S is mixed with live R and

injected into mice, the mouse dies. • WHY?

Searching for Genetic Material

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

Searching for Genetic MaterialOswald 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)

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.

• Noticed that:# of Adenine = # of Thymine# of Cytosine = # of Guanine

• “Chargaff’s Rule”

Chargaff's Rule (Data)Relative Proportions (%)

of Bases in DNA

ORGANISM A T G CHuman 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

C and G are held more tightly together because they are connected by three hydrogen bonds, whereas A and T are held by only two.

Discovering the structure of DNA

Maurice Wilkins (1952)• Studied DNA using x-ray

crystallography with another scientist named Rosalind Franklin

• He showed Franklin’s x-ray photograph without Franklin’s consent to Watson and Crick, which helped them discover DNA’s structure.

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

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

• 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

How was the structure of DNA discovered?

• 1953 – Watson and Crick– Wilkins shows Watson and Crick the x-ray

pictures from Franklin• This information gave Watson & Crick the evidence

to conclude DNA has a helical shape– Made model of DNA which was made up of

two chains of nucleotides

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

DNA Structure (PART 2)

Ms. Kim Honors Biology

DNA and Its Structure

• From 1953

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

DNA - basics• Deoxyribonucleic Acid• Stores and transmits genetic

info• Tells the cells which proteins to

make and when to make them• Made up of nucleotides

– Phosphate group– Sugar– Nitrogen bases

• Double helix structure

The Structure of DNA • Made out of nucleotides • Includes a phosphate group, nitrogenous base and 5-carbon pentose sugar

Nucleotide Structure

1 “link” in a DNA chain

A Polynucleotide• MANY

nucleotides (“links”) bonded together

Nucleotide Structure

DNA has a overall

negative charge b/c of

the PO4-3

(phosphate group)

The Structure of DNA Backbone = alternating P’s and 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 P & deoxyribose sugar

–STRONG!!!

Major Groove

Minor Groove

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

Nitrogen Bases (2 types)• Purines (small word, big base)

– Adenine– Guanine

• Pyrimidines– (big word, small base)

– Cytosine– Thymine

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

stacked pairs; WEAK bonds

Why Does a Purine Always Bind with A Pyrimidine?

DNA Double Helix• http://www.sumanasinc.com/webcont

ent/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…• Complementary strand:5’AATCGCTATAC3’

Template strand: 3’TTAGCGATATG5’