Seeking the Genetic Messenger DNA

1. Seeking the Genetic MessengerDNA St. John’s University Science Inquiry Sci1000C Prof. Victor Santos

2. DNA • Deoxyribonucleic acid • The most celebrated molecule of the 20th century • The structure was finally discovered by James Watson and Francis Crick in 1953, they won the Nobel Prize in 1962.

4. DNA • Structure? • Role? • Location?

5. structure

6. 2 strands • Helix • Made up of repeating subunits known as nucleotides • DNA interacts with proteins called histones to make chromosomes

7. Role • DNA controls the production of proteins in our body. • By controlling the production of proteins, it can control every aspect of our body.

8. location • DNA makes up our chromosomes located in the nucleus • The mitochondrion/chloroplast has DNA as well.

9. Help wanted! If you were to place an ad seeking DNA, what qualities would you list in the ad?

10. The genetic material must 1- Information 2- transmission 3- replication 4- variation

11. Seeking the genetic messenger • Since the time of Gregory Mendel (1865) it has been known that physical traits are passed on by discrete units. • What are these units made up of? • Protein vs Nucleic acid dilemma

12. Frederick Griffith Experiments with Streptococcus pneumoniae • Griffith studied a bacterium (pneumococci) now known as • Streptococcus pneumoniae • S. pneumoniaecomes in two strains • S = Smooth • Secrete a polysaccharide capsule • Protects bacterium from the immune system of animals • Produce smooth colonies on solid media

13. R = Rough • Unable to secrete a capsule • Produce colonies with a rough appearance

14. experiment • In 1928, Griffith conducted experiments using two strains of S. pneumoniae:type S and type R

16. conclusion • One of the first experiments to show that bacteria are capable of transferring genetic information through a process known as transformation. • But what is the transforming principle?

17. Avery/MacCleod/McCarty • In 1944, they demonstrated that the transforming principle was indeed nucleic acid and not proteins!

19. Hershey and Chase experiment (1952) • Used bacteriophages to finally prove that DNA is indeed the genetic material in a cell!!!!!!

21. Conclusion • DNA is indeed the genetic material

22. Experiments that led to the conclusion that the genetic material is found in the nucleus 1- J. Hammerling’s classic experiment demonstrated that the genetic material is indeed located in one part of the cell and not distributed all over. He worked with a type of Algae called Acetabularia. Acetabularia are single celled and asymmetrical.

24. How can he determine where the genetic material is found from these cells knowing that they are single celled organisms, capable of regeneration and are asymmetrical?

25. What conclusion can you draw from these results?

26. Let’s think • 1- what other experiment can be done to confirm that the foot actually contains the genetic material?

27. He decided to switch the top halves of each algae with the feet of the other.

29. Conclusion • The genetic material must be localized in the foot of the cell. • Hammerling looked under the microscope and was able to identified the nucleus on the foot of the cell!

30. Watson and Crick • In 1953 determined the structure of DNA only by drawing on the work of many scientists including Rosalind Franklin. • Prior to this, Rosalind Franklin, a chemist had used x-ray diffraction to discover that DNA is indeed a double helix.

31. DNA and RNA are large macromolecules with several levels of • complexity • 1. Nucleotides form the repeating units • 2. Nucleotides are linked to form a strand • 3. Two strands can interact to form a double helix • 4. The double helix folds, bends and interacts with proteins • resulting in 3-D structures in the form of chromosomes

32. NUCLEIC ACID STRUCTURE • The nucleotide is the repeating structural unit of DNA and RNA • It has three components • A phosphate group • A pentose sugar • A nitrogenous base

34. 4 bases

35. Complementary base pairs • Chargaff’s rule

38. recap • Film on DNA discovery