Chapter 12: DNA and RNA

1. Chapter 12: DNA and RNA SCCS Honors Biology

2. DNA • Deoxyribonucleic acid • A large polymer used to carry the genetic code of all living organisms

3. DNA – Heredity & Structure What we know about DNA was not discovered overnight! Many different scientists contributed information. Because of the efforts of all these scientists, we now have a model of DNA that consistently fits the observations we make. It also allows us to make useful predictions!

4. Griffith’s Experiment • Was trying to develop a vaccination for the pneumococcus bacteria.  • Vaccine- a prepared substance from killed or weakened disease-causing agents used to prevent future infections • He was working with two strains of bacteria.  • Rough - bacteria had a rough appearance in culture, non-virulent (doesn't kill) • Smooth - bacteria had a  smooth appearance in culture, virulent (kills)

5. Heat-killed, disease-causing bacteria (smooth colonies) Harmless bacteria (rough colonies Heat-killed, disease-causing bacteria (smooth colonies) Disease-causing bacteria (smooth colonies) Harmless bacteria (rough colonies) Control(no growth) Lives Dies of pneumonia Lives Dies of pneumonia Live, disease-causingbacteria (smooth colonies)

6. DNA as hereditary material • The Genetic Material is DNA – Alfred Hershey and Martha Chase, 1952 • Previously, scientists thought that proteins were the hereditary molecule • Hershey and Chase worked with viruses that infect bacteria called bacteriophages • Through a series of experiments, they were able to show that DNA, not protein, is the hereditary molecule.

7. Martha Chase (left) & Alfred Hershey (right)

8. Virus Structure DNA is located in the head. The outside and tail of the virus is made out of protein.

9. Virus ATTACKS!!

10. Bacteriophages ATTACK!!

11. Hershey – Chase Experiment – DNA in Viruses Radioactivity inside bacterium Phage infectsbacterium Bacteriophage with phosphorus-32 in DNA Phage infectsbacterium Bacteriophage with sulfur-35 in protein coat No radioactivity inside bacterium

12. Hershey & Chase Experiment • Concluded that the DNA of viruses is injected into the bacterial cells, while the viral proteins remain outside • The injected DNA molecules cause the bacterial cells to produce more viruses • DNA is the hereditary material – not proteins.

13. Wilkins & Franklin M.H.F. Wilkins and Rosalind Franklin, early 50’s Wilkins and Franklin studied the structure of DNA crystals using X-rays. They found that the crystals contain regularly repeating subunits. The X pattern produced by DNA suggested that DNA contains structures with dimensions of 2 nm, 0.34 nm, and 3.4 nm. The dark structures at the top and bottom indicate that some structure was repeated, suggesting a helix.

14. Rosalind Franklin X-ray diffraction image of DNA

15. Watson & Crick James Watson and Francis H.C. Crick, 1953 Watson and Crick used Chargaff's base data and Franklin’s X-ray diffraction data to construct a model of DNA. The model showed that DNA is a double helix with sugar-phosphate backbones on the outside and the paired nucleotide bases on the inside, in a structure that fit the spacing estimates from the X-ray diffraction data. Chargaff's rules showed that A = T and G = C, so there was complementary base pairing of a purine with a pyrimidine, giving the correct width for the helix. The paired bases can occur in any order, giving an overwhelming diversity of sequences.

16. Watson & Crick with their model of DNA

17. DNA Structure • Double Helix - twisted ladder • Made up of monomers called nucleotides • Nucleotides are composed of: • Deoxyribose sugar • Phosphate group • Nitrogenous base

18. Nitrogenous Bases • Two types: • Purines (two rings) • Pyrimidines (one ring) • Purines • Adenine and Guanine • Pyrimidines • Thymine and Cytosine

19. Purines Pyrimidines Adenine Guanine Cytosine Thymine Deoxyribose Phosphate group

20. Practice Pairing… TEMPLATE STRAND A C G G T A T G C C A T

21. Bonding TEMPLATE STRAND A C G G T A T G C C A T Weak HYDROGEN bonds form between the Nitrogen Base Pairs.

22. Chargaff’s rules: • Base pairing rule is A-T and G-C • Thymine is replaced by Uracil in RNA • Bases are bonded to each other by Hydrogen bonds • Discovered because of the relative percent of each base; (notice that A-T is similar and C-G are similar)

23. Erwin Chargaff

25. DNA Structure Backbone alternates with phosphate and sugar (deoxyribose) with the nucleotides formingthe rungs or steps of the ladder

26. The backbone of it all… TEMPLATE STRAND A C G G T A T G C C A T The backbone is made of alternating sugars and phosphates. - Remember: Sugar ALWAYS attaches to the Nitrogen base

28. Nucleotide Hydrogen bonds Sugar-phosphate backbone Key Adenine (A) Thymine (T) Cytosine (C) Guanine (G)

29. DNA (cont’d) • DNA is found packed in the nucleus of eukaryotic organisms; it is found in the cytoplasm of prokaryotic organisms • DNA is packed together and wrapped around special proteins called HISTONES • DNA bound protein is called CHROMATIN • When chromatin condenses (gets thicker) it forms CHROMOSOMES

30. So Remember: DNA  Chromatin  Chromosomes

31. Nucleosome Chromosome DNA double helix Coils Supercoils Histones

32. DNA Replication Part 2

33. DNA & RNA continued! • Before mitosis (during S phase of interphase) , a complete copy of a cell’s DNA is made through a process called replication. • When a cell divides, each daughter cell gets one complete copy of the DNA. • Similar to photocopying a document – the end result is two identical documents that contain the same information. • Now that we know something about DNA’s structure, lets look at how it replicates.

34. Steps of DNA Replication • DNA must unwind and break the hydrogen bonds • Each strand is used as a template (blueprint) • Two new strands of DNA are formed from the original strand by the enzyme DNA Polymerase

35. During replication, an enzyme called helicase “unzips” the DNA molecule along the base pairing, straight down the middle. • Another enzyme, called DNA polymerase, moves along the bases on each of the unzipped halves and connects complementary nucleotides. • What do we mean by complementary nucleotides?

36. Original strand New strand DNA polymerase Growth DNA polymerase Growth Replication fork Replication fork Nitrogenous bases Original strand New strand

37. Because of Chargaff’s rule, only the correct, complementary bases will fit, so chances are good that the DNA polymerase will make a perfect copy. • Mistakes happen!  Mutation! Is this frog likely to survive long in the wild?

38. DNA Replication Animation

39. P M A T • When DNA polymerase finishes, the nucleus has two identical (excluding mutations) copies of the original DNA molecule. Now the cell can proceed with mitosis. • The long DNA molecules condense into chromosomes. (prophase) • Chromosomes line up in center of cell (metaphase) • Spindle fibers attach to centromeres (anaphase) • Sister chromatids move to opposite sides of cell (telophase) • Cytokinesis happens, and BOOM – two new cells.

40. Protein SynthesisPart 3Transcription and Translation

41. DNA’s Purpose • DNA has genes that code for the synthesis (creation) of specific PROTEINS • Here’s the problem… • Where is DNA located? • Nucleus • Where does Protein Synthesis occur? • At ribosomes in the cytoplasm • Can DNA ever leave the nucleus? • No.

42. RNA • Ribonucleic acid • Single-stranded • Sugar is ribose • Thymine is replaced by URACIL

43. DNA Structure: Double stranded Sugar: Deoxyribose Bases: Adenine Guanine Cytosine Thymine RNA Structure: Single-stranded Sugar: Ribose Bases: Adenine Guanine Cytosine Uracil Differences between DNA and RNA

44. Transcription- how RNA is made • Just as DNA polymerase makes new DNA, a similar enzyme called RNA polymerase makes new RNA. • RNA polymerase temporarily separates the strands of a small section of the DNA molecule. • This exposes some of the bases of the DNA molecule. • Along one strand, the RNA polymerase binds complementary RNA nucleotides to the exposed DNA bases. • An exposed thymine on the DNA strand matches up with an adenine; an exposed cytosine on the DNA matches up with a guanine base; an exposed adenine DNA base matches up with URACIL!

45. As the RNA polymerase moves along, it makes a strand of messenger RNA (mRNA). • It is called messenger RNA because it carries DNA’s message out of the nucleus and into the cytoplasm. • mRNA is SINGLE STRANDED! • When the RNA polymerase is done reading the gene in the DNA, it leaves. • The separated DNA strands reconnect, ready to be read again when necessary. • mRNA moves out of the nucleus and finds a ribosome • On the ribosome, amino acids are assembled to form proteins in the process called translation.

46. DNA Transcription

47. Types of RNA: • Messenger RNA (mRNA) • carries information from DNA to ribosome • Transfer RNA (tRNA) • Carries amino acids • Ribosomal RNA (rRNA) • Makes up ribosomes

48. Messenger RNA Ribosomal RNA Transfer RNA Bringamino acids toribosome Combine with proteins tRNA mRNA Carry instructions rRNA DNA Ribosome Ribosomes RNA can be also called which functions to also called which functions to also called from to to make up

49. Part 4- • Translation- the Ultimate Goal! • Going from mRNA to the final product

50. Decoding the Information in DNA • How does DNA (a twisted latter of atoms) control everything in a cell and ultimately an organism? • DNA controls the manufacture of all cellular proteins including enzymes • A gene is a region of DNA that contains the instructions for the manufacture of on particular polypeptide chain (chain of amino acids) DNA is a set of blueprints or code from making proteins