Unraveling DNA: The Molecule of Life and Its Crucial Functions

1. DNA Instructions for life

2. What does DNA do? • This very large molecule called Deoxyribonucleic acid contains information. • DNA information codes for proteins that make up muscle, enzymes, & the structures of organisms. • A gene is a section of DNA coding for a protein.

3. Four Key Features • DNA has a uniform diameter (Franklin) • DNA is a double helix (Watson and Crick) • Adenine pairs with Thymine & Guanine pairs with Cytosine (Chargaff) • The two strands are built in opposite directions.

4. The parts—backbone • Backbone or rails of the ladder: alternating deoxyribose and phosphate. • Deoxyribose: a sugar • Phosphate: a negative ion containing phosphorus • Alternating pattern

5. The rungs of the ladder • Nitrogenous bases contain nitrogen • Pairs: • A-T • G-C • Pyrimidines: 1 ring • Thymine • Cytosine • Purines: 2 rings • Adenine • Guanine

6. Join 2 strands • Hydrogen bonds connect A-T or G-C pairs. • H bonds are weak forces between partial positive and negative charges on atoms—works like magnets.

7. History of DNA’s Discovery • Patterns of Inheritance--1857 • Gregor Mendel studied peas the and passage of traits from one generation to another. • What could carry the information from one individual to another?

8. Frederick Griffith--1928 • Experiment: mice and 2 types of pneumonia (virulent and non-virulent). • Proved chemical transfer of information.

9. Erwin Chargaff—1950’s • Chargaff studied the DNA of different species from different kingdoms and different phyla. • The amount of Adenine was close to equal to the amount of Thymine. • The amount of Guanine was close to the amount of Cytosine. • Chargaff’s Rule • http://www.dnalc.org/resources/3d/21-chargaff-ratios.html

10. Rosalind Franklin—1950’s • Studied the structure of DNA using a technique called X-ray diffraction. • The repeating ‘x’ patterns imply a twisting coiled shape: helix. • The molecule has uniform diameter and uniform repeat to the twist.

11. Francis Crick and James Watson—1952 • They worked to develop three dimensional model of DNA that would explain properties of the molecule. • Franklin’s work gave them a vital clue. • The molecule was a double helix with the bases making the rungs of a ladder. • One page paper was published April 1953

12. DNA Replication • To pass information to another organism, the data which is stored in the DNA must be copied. • Process is called DNA Replication • A replica is an exact copy • How does DNA replicate? • How does its structure work to make copies?

13. Replication • Both strands carry the same information. • 1) Unwind the helix. • 2) Unzip the strands to make two templates to use in making copies. • 3) Build a complementary strand one nucleotide at a time for two identical molecules. Replication Fork

14. Build a complementary strand • Follow Chargaff’s Rule: A=T and G=C • Find the bases that complement this strand: A T TT GCG TAACCGA TAAA CGCAT T GGCT

15. Does the new DNA have any of the original molecule in it? • Which model would work?

16. Helicase • Enzyme that unwinds the double helix. • Name comes from the helix shape of DNA that the enzyme straightens out. Helicase

17. DNA Polymerase • This protein enzyme that connects the nucleotides together to make the polymer. • It proofreads the sequences. • Most accurate enzyme Polymerase DNA Polymerase

18. DNA Packaging • DNA is an enormously long molecule. • How do you pack and move DNA? • http://www.dnalc.org/resources/3d/07-how-dna-is-packaged-basic.html

19. CoilingSupercoiling • Wind DNA around histone core like a spool of thread. • Nucleosome • Wind coiled DNA into second supercoil. • Condensed chromosome

20. Resources • http://www.dnai.org/timeline/