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Agenda March 8th Part I • Turn in 3 HW Handouts on Scientific Method • Quiz # 1 • Video: The Double Helix • Notes: DNA Structure, DNA Scientists • Lab # 10: Extracting DNA • Break • In Class Reading and Questions: – The Structure of DNA: Cooperation and Competition 1 2 3 Review: What is DNA? • DNA is a molecule that contains ALL of an organism’s genetic material and is therefore responsible for HEREDITY • A strand of DNA contains many GENES all of which code for PROTEINS • Each of these proteins has a different function in a cell Two scientists, James Watson and Francis Crick, were the first to discover the structure of DNA They referred to it as a DOUBLE HELIX because it contains two complementary strands, each of which is shaped like a spiral staircase DNA stands for Deoxyribonucleic Acid DNA is made up of 3 main components: Deoxyribose – a sugar molecule Phosphates – which make up part of the backbone Nitrogenous bases – Thymine, Adenine, Guanine, Cytosine DNA Structure 8 DNA • Two strands coiled called a double helix • Sides made of a pentose sugar Deoxyribose bonded to phosphate (PO4) groups by phosphodiester bonds • Center made of nitrogen bases bonded together by weak hydrogen bonds 9 DNA Double Helix “Rungs of ladder” Nitrogenous Base (A,T,G or C) “Legs of ladder” Phosphate & Sugar Backbone 10 Helix • Most DNA has a right-hand twist with 10 base pairs in a complete turn • Left twisted DNA is called Z-DNA or southpaw DNA • Hot spots occur where right and left twisted DNA meet producing mutations 11 DNA • Stands for Deoxyribonucleic acid • Made up of subunits called nucleotides • Nucleotide made of: 1. Phosphate group 2. 5-carbon sugar 3. Nitrogenous base 12 DNA Nucleotide Phosphate Group O O=P-O O 5 CH2 O N C1 C4 Sugar (deoxyribose) C3 C2 Nitrogenous base (A, G, C, or T) 13 Pentose Sugar • Carbons are numbered clockwise 1’ to 5’ 5 CH2 O C1 C4 Sugar (deoxyribose) C3 C2 14 5 DNA O 3 3 P 5 O O C G 1 P 5 3 2 4 4 P 5 P 2 3 1 O T A 3 O 3 5 O 5 P P 15 Antiparallel Strands • One strand of DNA goes from 5’ to 3’ (sugars) • The other strand is opposite in direction going 3’ to 5’ (sugars) 16 Nitrogenous Bases • Double ring PURINES Adenine (A) Guanine (G) A or G • Single ring PYRIMIDINES Thymine (T) Cytosine (C) T or C 17 Base-Pairings • Purines only pair with Pyrimidines • Three hydrogen bonds required to bond Guanine & Cytosine 3 H-bonds G C 18 •Two hydrogen bonds are required to bond Adenine & Thymine T A 19 Question: • If there is 30% Adenine, how much Cytosine is present? 20 Answer: • There would be 20% Cytosine • Adenine (30%) = Thymine (30%) • Guanine (20%) = Cytosine (20%) • Therefore, 60% A-T and 40% C-G 21 Lab 10 DNA extraction from bananas !!! 22 Banana DNA Lab • Purpose: to extract DNA from the fruit of a bananas… 23 Lab Objectives • Follow steps for extracting DNA from plant cells • Observe DNA (Yes, you can actually see DNA) !!! Banana DNA Lab • Follow procedure on the handout • Complete pages 95-99 25 Lab Steps • • • • • • Read the directions !!! Squish the fruit to a slush in the baggie Mix in detergent solution Filter extract through a coffee filter Layer cold alcohol over the extract Repeat steps for the banana 26 Lab Closure Know the reason for each of these steps ! • Why do you squish the fruit to a slush ? • Why do you mix in detergent solution • Why filter extract through a coffee filter ? • Why layer cold alcohol over the extract ? 27 Match these steps 28 Review Questions 1. In what part of the cell is DNA found ? 2. What are the units (building blocks) of DNA called ? 3. Those units are made up of what 3 parts ? 4. What are the names of the 4 bases ? 5. How do the bases pair up in a DNA molecule ? What are the complementary bases to this DNA strand: TTACCTGCAGGC 6. How does DNA impact our lives ? Answers 1. DNA is found in the nucleus 2. The units (building blocks) of DNA are called nucleotides 3. Those units are made up of these 3 parts: sugar, phosphate, base 4. The names of the 4 bases are adenine, guanine, cytosine, thymine 5. A pairs with T and G pairs with C 6. TTACCTGCAGGC pairs with AATGGACGTCCG What are some common uses of DNA technology today ? • DNA evidence from crime scenes (forensics) • Genetic engineering of plants, animals • Cloning of research animals • Genetic screening of individuals for hereditary diseases • Paternity tests •Dog Poop Tests !!!! 31 Testing Dog Poop DNA • DNA testing can identify dogs through the poop they leave behind… • This is bad news for those who don’t clean up after their pets…They face some pretty stiff fines !!! 32 Objectives To create a timeline of scientists who have been important in the discovery of DNA as the molecule of heredity – List scientists and their contributions… – Explain how the discovery of DNA structure was both an example of cooperation and an example of competition 33 DNA Scientists… • Fredrich Miescher • Frederick Griffith • Oswald Avery, Colin Macleod, Maclyn McCarty • Erwin Chargaff • Alfred Hershey and Martha Chase • Rosalind Franklin and Maurice Wilkins • Linus Pauling • James Watson and Francis Crick34 Timeline of Discoveries: The Search for DNA 35 Early DNA Scientists 36 37 38 History of DNA • Early scientists thought protein was the cell’s hereditary material because it was more complex than DNA • Proteins were composed of 20 different amino acids in long polypeptide chains 39 Transformation • Fred Griffith worked with virulent S and nonvirulent R strain Pneumoccocus bacteria • He found that R strain could become virulent when it took in DNA from heat-killed S strain • Study suggested that DNA was probably the genetic material 40 Griffith Experiment (1928) 41 Avery Experiment (1943) 42 Avery Experiment 43 Erwin Chargaff (1950) 44 Discovery of DNA Structure • Erwin Chargaff showed the amounts of the four bases on DNA ( A,T,C,G) • In a body or somatic cell: A = 30.3% T = 30.3% G = 19.5% C = 19.9% 45 Erwin Chargaff 46 Chargaff’s Rule • Adenine must pair with Thymine • Guanine must pair with Cytosine • The bases form weak hydrogen bonds T A G C 47 Hershey and Chase (1952) 48 Hershey and Chase 49 History of DNA • Chromosomes are made of both DNA and protein • Experiments on bacteriophage viruses by Hershey & Chase proved that DNA was the cell’s genetic material Radioactive 32P and 32s were injected into bacteria. DNA has p (phosphorus) but not s (sulfur). The 32P showed up in the bacteria 50 Rosalind Franklin (1953) 51 Rosalind Franklin 52 Rosalind Franklin copyright cmassengale 53 DNA Structure • Rosalind Franklin took diffraction x-ray photographs of DNA crystals • In the 1950’s, Watson & Crick built the first model of DNA using Franklin’s x-rays 54 Watson and Crick (1953) 55 Linus Pauling: DNA as a Triple Helix ??? copyright cmassengale 56 Watson and Crick 57 Don’t Forget Frederick Sanger 1975 Sequencing of DNA Bases 58 Structure of DNA Reading, Questions 1. What were the four initial clues that gave insight into the importance and structure of DNA? 2. What are the 3 basic components of DNA ? 3. What are the 4 different DNA bases ? 4. How does this article show that science relies on communication within a diverse scientific community ? 59 Structure of DNA Reading, Questions 5. What technology came available in the first half of the 20th century that made solving the structure of DNA possible ? How did it help ? 6. Compare the approaches of Wilkins and Franklin and the approaches of Watson and Crick in solving DNA’s structure 60 Structure of DNA Reading, Questions 7. What was image “B51”? Who took it ?How did it help solve the puzzle of DNA’s structure ? 8. How do the bases pair in DNA? How does this agree with the previous mysterious base ratios ? 9. How is reporting one’s findings and sharing ideas essential for scientific progress ? How did it make solving 61 the structure of DNA possible ? Agenda March 8th Part II • • • • • Notes: DNA Replication Notes: Proteins, Protein Structure Lab # 5: Biomolecules II Break Protein Synthesis Video • In Class Reading and Questions: – Molecular Level of Genetics • Video: One Wrong Letter • Review for Exam I (Lectures 1,2,3,4) 62 DNA Replication 63 Essential Question • Think !!! How does the structure of a double helix ensure that all cells of an organism get the same genetic code ??? Lesson Objectives 1. Explain how DNA is replicated (copied) Replication Facts • DNA has to be copied before a cell divides • DNA is copied during the S or synthesis phase of interphase • New cells will need identical DNA strands 66 Synthesis Phase (S phase) • S phase during interphase of the cell cycle • Nucleus of eukaryotes S DNA replication takes place in the S phase. phase G1 interphase G2 Mitosis -prophase -metaphase -anaphase -telophase 67 DNADNADNADNADNADNA Replication Notes DeoxyriboNucleic Acid REPLICATION VOCABULARY • • • • • • • • Double Helix Hydrogen Bonds Sugar-Phosphate Backbone Complementary Template Replication DNA Polymerase Helicase DeoxyriboNucleic Acid REPLICATION • Replication is the duplication of DNA that occurs in the S Phase of Cell Cycle • The two strands of DNA separate and each acts as a template for the formation of a new strand. Copying DNA • Matching bases allows DNA to be easily copied Making new DNA • Copying DNA – replication – DNA starts as a double-stranded molecule • matching bases (A:T, C:G) – then it unzips… DNA replication • Strands “unzip” at the weak bonds between bases Enzyme: Helicase breaks the hydrogen bonds DNA replication DNA bases in nucleus • Enzyme DNA polymerase – DNA polymerase – adds new bases Copying DNA • Build daughter DNA strand – use original parent strand as “template” – add new matching bases – synthesis enzyme = DNA polymerase DNA Polymerase New copies of DNA • Get 2 exact copies of DNA to split between new cells DNA polymerase DNA polymerase Copied & Paired Up Chromosomes DeoxyriboNucleic Acid REPLICATION • There is only a 1 in a million chance that there will be an error – If there is an error it is called a mutation (change in DNA) • The cell proofreads the DNA and repairs any mutations it might find – So after this process a chance of mutation is 1 in a billion Question: • What would be the complementary DNA strand for the following DNA sequence? DNA 5’-CGTATG-3’ 79 Answer: DNA 5’-CGTATG-3’ DNA 3’-GCATAC-5’ 80 Review Proteins !!! Text pages 99-105 81 82 Molecular Genetics Reading and Questions • Read through the article… • Diagram in your notes the role of m-rna and t-rna • Answer questions 1-18 in your notebooks • Be prepared to share your responses… • Finished ? Work on Study Guide 83