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’