DNA –The Language Of Life

1. DNA –The Language Of Life Chapter 11

2. 11.1 What is the chemical in genes? • Computer keyboard analogy. • > 100 keys ; correct order. • Students in the classroom. • Same parts-arms,legs, eyes etc. • All people have the same chemicals. • It’s the combination of chemicals that produces the many different characteristics. • Just as letters form sentences, chemicals form DNA.

3. DNA is the chemical of genes • In the cell cycle- DNA replicates DNA divides in mitosis/meiosis. • Each cell has genetic blueprint instructions.

4. The story of how we learned DNA was the genetic material: • Experiments- Griffith- Transforming Factor. • Pneumonia- caused by Streptococcus pneumoniae. • 2 Strains of bacteria. • Smooth strain- capsule. • Caused pneumonia in mice. • Rough strain - no capsule. • Did not cause pneumonia in mice. • Heat killed smooth strain. • Did not cause pneumonia in mice. • Combined heat-killed smooth strain and rough strain bacteria. • Caused disease in mice .

5. Griffith’s Experiment Figure 11-1 Griffith showed that although a deadly strain of bacteria could be made harmless by heating it, some factor in that strain is still able to change other harmless bacteria into deadly ones. He called this the "transforming factor."

6. What happened? • Griffith examined the blood of the dead mice and found smooth strains of bacteria. • The Rough strain was transformed to become smooth. • All descendents of the transformed bacteria were also smooth and caused disease. • Griffith called the substance “transforming factor”.

7. Experiments to identify the “transforming factor” • Scientists knew chromosomes were involved in inheritance. • Chromosomes are made up of proteins and DNA. • Most scientists thought the hereditary material was in protein rather than DNA.

8. Avery’s Experiment • Avery used enzymes. • After protein destroying enzymes were used on Griffith’s heat treated and live rough mixture. • rough bacteria were transformed showing that protein was not the transforming factor. • Then DNA destroying enzymes were used. • rough bacteria were not transformed. • DNA was the transforming factor.

9. Hershey and Chase Bacteriophage Experiment

10. Hershey & Chase’s Bacteriophage Experiment Proves DNA is the genetic material • Viruses are not cells. • nucleic acid wrapped in a protein coat. • only reproduce by infecting a living cell. • viral genetic material directs host cell to make more virus copies. • Bacteriophage -viruses that attack bacteria. • Bacteriophage of Hershey &Chase. • outer coat of protein; inner core of DNA.

11. Radioactive isotope of sulfur labels phage protein coat only. • Radioactive isotope of phosphorous labels phage DNA only. • When only phage protein coats were labeled, radioactivity was detected outside of the cell. • When phage DNA was labeled radioactivity was detected inside the cell. • Conclusion : phage DNA enters the bacterial cell , NOT protein. • DNA is the genetic material !

12. 11.2 Structure of DNA pp 229-231

13. Nucleic Acids- • Function - store and transmit genetic information. • Nucleic Acids- made up of many units of nucleotides(monomers) • Nucleotides are the building blocks. • DNA- Deoxyribonucleic Acid • 4 different nucleotides. • A=adenine • G=guanine • C=cytosine • T=thymine

14. NUCLEOTIDE STRUCTURE 3 PARTS OF A NUCLEOTIDE: • Deoxyribose - 5 Carbon sugar • Phosphate Group- Phosphorous atom with 4 atoms of oxygen • Nitrogenous base. • Single or double stranded rings of carbon and nitrogen

15. The 4 nucleotides of DNA: • The nitrogenous base is the difference. Pyrimidines- single-ring structures. • Thymine- T. • Cytosine- C. Purines- double-ring structures. • Adenine- A. • Guanine- G. • The letters T,C,A,G are used to represent the bases and also the nucleotides that contain them.

16. Sugar-phosphate DNA backboneDouble helix (ladder )model • Outside of the ladder • Repeating pattern • Sugar of one nucleotide is connected to the phosphate group of the next. • Attached nitrogenous bases are on the inside (rungs)of the double helix model.

17. Nucleotide chains can vary in length. • Nucleotides can combine in many different sequences represented by the letter symbols. • CTAGCCTTGAC Nitrogenous Base Pairing: A=T ( by 2 hydrogen bonds) G=C (by 3 hydrogen bonds) Called Complimentary Base Pairing. Base-pairing rule- each base must pair up with its complementary base.

18. Double Helix Structure • 1950s- Franklin- X-ray crystallography. • Showed basic shape to be a helix • 1953- Watson and Crick model • Used Franklin’s photos • Twisting shape-double helix ; 2 nucleotides twist around each other. • Sugar-phosphate backbone on outside • Nitrogenous bases on the inside joined by hydrogen bonds.

19. 11.3 DNA Replication-the process of copying a DNA molecule. • The cell uses a “negative” as a copy to make more DNA. • Template mechanism. • 2 strands of the double helix separate. • A series of enzymes are involved. • The enzymes “unzip” the molecule of DNA, breaking the hydrogen bonds between the base pairs. • Each strand acts as a negative template for a new, complementary strand to form. • Base-pairing rules are followed.

20. DNA Replication Continued • DNA polymerases- the principal enyme • enzymes that make the bonds between the nucleotides of the new DNA strand. • They also “proof-read” each new DNA. • DNA replication begins at specific sites called points of origin. • Replication proceeds in outward directions from the points of origin resulting in replicating bubbles. • The parent DNA strands open up as new daughter strands grow.

21. Result of DNA replication: • Result- 2 double stranded DNA molecules; each one has an old and complementary new strand. • DNA replication occurs before a cell divides.