Presentation on theme: "DNA – The Scientists and Their Discoveries. Frederick Griffith (1928) Experiment – worked with bacteria and injected into mice Conclusion – transforming."— Presentation transcript:
DNA – The Scientists and Their Discoveries
Frederick Griffith (1928) Experiment – worked with bacteria and injected into mice Conclusion – transforming material is genetic material Transformation – when 1 cell is changed to another cell permanently
Frederick Griffith Disease-causing bacteria (smooth colonies) Harmless bacteria (rough colonies) Heat-killed, disease- causing bacteria (smooth colonies) Control (no growth) Heat-killed, disease-causing bacteria (smooth colonies) Harmless bacteria (rough colonies) Dies of pneumoniaLives Live, disease-causing bacteria (smooth colonies) Dies of pneumonia
Oswald Avery (1944 ) Experiment – to determine which molecule in a cell transformed expanded on Griffith’s experiment Conclusion – DNA stores and transmits genetic information throughout generations
Alfred Hershey and Martha Chase (1952) Experiment – used radioactive proteins and radioactive DNA in bacteriophages Bacteriophage – a virus that infects bacteria Conclusion – confirmed that DNA was genetic material
Hershey and Chase
Rosalind Franklin (1952) Experiment – used x-ray diffraction to see structure of DNA X-ray diffraction—powerful x-rays shown through a concentrated DNA sample Worked with Maurice Wilkins Conclusion – DNA is a helix
What is X-ray Diffraction?
James Watson & Francis Crick (1953) Experiment – Built many 3-D models of DNA; Used Franklin, Wilkins, Pauling’s work Conclusion – DNA is a double helix, a twisted ladder. Each nucleotide made of sugar, phosphate, and base. “ Sides”: sugar and phosphates “Rungs”: bases Bases are held together by hydrogen attraction
Erwin Chargaff (1947) Experiment – Analyzed the amounts of the four bases in different organism’s DNA Conclusion –base-pairing rules adenine = thymine (A-T) cytosine = guanine (G-C)
Erwin Chargaff Percentage of Bases in Four Organisms Source of DNAATGC Streptococcus Yeast Herring Human Streptococcus Yeast Herring Human
Nucleotides: Page 291 AdenineGuanine Cytosine Thymine Phosphate group Deoxyribose
DNA Structure and DNA Replication
DNA Structure DNA stands for Deoxyribonucleic Acid Shape: Double helix Monomers: Nucleotides Nucleotide has 3 parts: Sugar (deoxyribose), phosphate, and a nitrogenous base Bases are held together by hydrogen attractions. Why are hydrogen attractions important in DNA’s structure?
Four Nitrogenous Bases Adenine (A), Guanine (G), Cytosine (C), Thymine (T) Purines (double ring) – Adenine and Guanine P y rimidines (single ring) – Cytosine and Thymine Chargaff’s rule: Adenine pairs with thymine. A –T T – A Guanine pairs with cytosine. G – C C – G
So if every living thing has the same 4 bases, how are we so different? It’s the SEQUENCE!! The order of those 4 nitrogen bases determines whether you are a human or a dog! It also determines traits of that organism (why you look different than your shoulder partner or sibling.)
A closer look at DNA: How DNA condenses Chromosome Supercoils Chromatin Histones DNA double helix Centromere
What is DNA Replication? The process of making copies of DNA during S phase of interphase in the nucleus Makes sure that a daughter cell will have a complete set of chromosomes Original strand of DNA serves as a template for 2 new strands Template: a pattern; an original model Each new strand will be identical to the original strand because of Chargaff’s rule.
How does DNA replication work? 1) Helicase unwinds the double helix, forming a “replication fork,” where replication takes place 2) DNA polymerase bonds the necessary nucleotides to complement the parent/original DNA strand to complete 2 new DNA molecules 3) DNA polymerase also “proofreads” the new DNA strand to make sure it is an exact copy of the original DNA
DNA Replication Facts: DNA polymerase can only work in one direction so: 2 new strands of DNA are made in opposite directions One strand is made in sequence of nucleotides The other strand is what we call the “lagging strand” because nucleotides are added in fragments
1. Helicase unwinds/unzip s DNA strand 2. DNA Polymerase complements the original DNA strand using Chargaff’s Rules A-T C-G 3.. DNA Polymerase proofreads the exact copy Parent New Parent New
DNA Growth Replication fork DNA polymerase New strand Original strand DNA polymerase Nitrogenous bases Replication fork Original strand New strand