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http://faculty.uca.edu/~johnc/mbi1440.htm DNA and RNA Chapter 12-1 http://www.wappingersschools.org/RCK/staff/teacherhp/johnson/visualvocab/mRNA.gif GENETIC MATERIAL In the 1900’s scientists began asking questions about genes: • What is a gene made of? • How do genes work? • How do genes determine characteristics of organisms? SEE GRIFFITH’s EXPERIMENT 1928 – Frederick Griffith looked at pneumonia bacteria trying to figure out what made people die S (SMOOTH) strain - killed mice R (Rough) strain -mice lived Images from: http://microvet.arizona.edu/Courses/vsc610/mic205/griffith.jpg If he heated the LETHAL strain first _______________ . . . mice lived. The heat killed bacteria were no longer LETHAL. Images from: http://microvet.arizona.edu/Courses/vsc610/mic205/griffith.jpg Images from: http://microvet.arizona.edu/Courses/vsc610/mic205/griffith.jpg BUT. . . If he mixed heat-killed LETHAL bacteria with live harmless bacteria . . . mice DIED ! ________________ When he looked inside dead mice, he found LIVE LETHAL ______________ bacteria! Somehow the heat killed LETHAL bacteria passed their characteristics to the harmless bacteria. See a video clip about GRIFFITH’S EXPERIMENTS) Griffith called this process TRANSFORMATION __________________ because one strain of bacteria had been changed permanently into another. But what was the factor that caused the transformation? A protein ? A lipid ? A nucleic acid ? A carbohydrate ? DO PROTEINS CARRY THE GENETIC CODE? At the time most scientists believed proteins that _________ had to be the molecules that made up genes. There were so many different kinds proteins and DNA seemed to be too monotonous . . . repeating the same 4 subunits. ___ http://en.wikipedia.org/wiki/Oswald_Avery 1944Oswald Avery’s team of scientists repeat Griffith’s experiments looking for the transforming molecule. After heat killing the LETHAL Pneumonia bacteria, he treated them with digestive enzymes that destroy specific kinds of molecules. If proteins, polysaccharides, lipids, or RNA’s were destroyed .. . Transformation still occurred! ______________________________ http://cystitis-cystitis.com/Images/testtube.jpg http://faculty.uca.edu/~johnc/mbi1440.htm But when they treated the heat-killed LETHAL bacteria with enzymes to DNA there was NO destroy _____ transformation! . . . the mice lived! DNA was the molecule that caused the genetic change. http://web.jjay.cuny.edu/~acarpi/NSC/12-dna.htm GRIFFITH EXPERIMENT (PNEUMONIA-RAT) Showed genetic ____________ material could be passed between bacteria & cause a change. AVERY EXPERIMENT (Digestive enzymes) showed that the genetic material DNA was _____ Scientists are skeptical… it takes more than one experiment to convince them. 1952-Alfred Hershey and Martha Chase experimented with viruses that infect bacteriophages bacteria = _________________ Knew bacteriophages were made of proteins and _______ DNA ________ Hear about their cool experiment http://www.mun.ca/biology/scarr/Chase_&_Hershey_1953.jpg BACTERIAL VIRUSES http://faculty.uca.edu/~johnc/mbi1440.htm http://www.mun.ca/biology/scarr/hersheychase-experiment.jpg HERSHEY-CHASE BLENDER EXPERIMENT only DNA not protein Showed_______________ entered cell during infection. Conclusion: Genetic material ______________in virus was DNA _____ not protein But what is the structure of DNA? 1. Structure must allow it to carry info from generation to generation 2. Structure must allow info to be put to work in the form of traits 3. Structure must be easily copied during mitosis Chargaff’s rule • Percent of G and C are equal in any DNA sample • Percent of A and T are equal in any DNA sample • No one had any idea why!!! Rosiland Franklin (1950) • Shot X rays at DNA molecule and got a pattern that reveals 2 strands in a helix with nitrogenous bases in center. DNA is a DOUBLE HELIX http://www.time.com/time/time100/scientist/profile/watsoncrick.html James Watson and Francis Crick discovered of the structure of DNA in 1953 By using models of nucleotides and evidence NUCLEIC ACIDS are built from subunits called ____________________ NUCLEOTIDES Image by: Riedell SUGAR in DNA is deoxyribose ________________ Figure 12–7 Structure of DNA Section 12-1 Nucleotide Hydrogen bonds Sugar-phosphate backbone Key Adenine (A) Thymine (T) Cytosine (C) Guanine (G) NITROGEN BASES in DNA _____________= A ADENINE _____________ =G GUANINE _____________ CYTOSINE = C ______________ THYMINE = T No URACIL DEOXYRIBONUCLEIC ACID DOUBLE ______________ STRANDED Image from: http://www.tokyo-med.ac.jp/genet/picts/dna.jpg Backbone (sides of ladder) made of PHOSPHATES _____________ and sugars _____________ Nitrogen bases =“Steps of ladder” A Phosphate group G C Deoxyribose sugar T Purines (2 rings) Pyrimidines (1 ring) © Pearson Education Inc, publishing as Pearson Prentice Hall. All rights reserved CHARGAFF’S RULES A = T G = C _________ _________ At time no one knew why… now we know its because Adenine always bonds THYMINE across with____________ Guanine always bonds CYTOSINE across with ____________ Image from: http://evolution.berkeley.edu/evosite/evo101/images/dna_bases.gif DOUBLE HELIX Hydrogen _____________ bonds between nitrogen bases hold the two strands together. Image from: http://evolution.berkeley.edu/evosite/evo101/images/dna_bases.gif Check your understanding • • • • • What did Griffith discover? How? What did Avery discover? How? What did Hershey and Chase discover? How? What is Chargaff’s rule? What did Rosiland Franklin contribute to the discovery of DNA? • Who solved the structure of DNA? • Describe the structure of DNA. CHROMOSOMES & DNA REPLICATION 12-2 Part 1: Chromosomes Chromosome Structure in Prokaryotes Approximately 5 million base pairs 3,000 genes Chromosome E. coli bacterium Bases on the chromosome Chromosome in bacteria is: SINGLE ______________ CIRCULAR ______________ CYTOPLASM (NO nucleus) Found in __________ © Pearson Education Inc, publishing as Pearson Prentice Hall. All rights reserved DNA in EUKARYOTES is packaged into chromosomes http://www.paternityexperts.com/images/DNA-of-life.jpg Humans have approximately 3 billion base pairs (1 m long) 30,000 genes THINK ABOUT IT How could you get this piece of string into this small container? http://www.artzooks.com/files/3966/AZ533823_320.jpg http://www.mivaroo.com/sites/toyconnection.com/ Chromosome Structure of Eukaryotes © Pearson Education Inc, publishing as Pearson Prentice Hall. All rights reserved Chromosome Nucleosome DNA double helix Coils Supercoils DNA is: in multiple ______________ chromosome bundles ______________ Found in __________ nucleus Histones Chromosome Structure of Eukaryotes © Pearson Education Inc, publishing as Pearson Prentice Hall. All rights reserved Eukaryotic chromosomes are Nucleosome made of PROTEINS DNA _____ & __________ called ___________ HISTONES Together the DNA & histone proteins forms a bead-like NUCLEOSOME structure called a ______________ Histones DNA double helix © Pearson Education Inc, publishing as Pearson Prentice Hall. All rights reserved Chromosome Structure of Eukaryotes Nucleosome Chromosome DNA double helix Coils Supercoils Histones Nucleosomes pack together to form thick coiled fibers. When cell is NOT dividing, DNA is spread out in nucleus as CHROMATIN (Allows reading of code) ___________. Chromosome Structure of Eukaryotes © Pearson Education Inc, publishing as Pearson Prentice Hall. All rights reserved Chromosome Nucleosome DNA double helix Coils Supercoils When cell gets ready to divide, the fibers pack even more tightly to form chromosomes ___________.(Makes it easier to move DNA during mitosis) Histones Part 2: DNA replication Image from: http://evolution.berkeley.edu/evosite/evo101/images/dna_bases.gif HOW IS DNA COPIED? The structure of DNA explains how it can be copied. Each strand has all the info needed to construct matching the __________other half. If strands are separated, base-pairing _____________ rules allow you to fill in the complementary bases. Figure 12–11 DNA Replication Section 12-2 New strand Original strand DNA polymerase Growth DNA polymerase Growth Replication fork Replication fork New strand Original strand Nitrogenous bases Sites where strand separation and replication forks replication occur are called _____________ REPLICATION STEPS 1.Enzymes “unzip” molecule by breaking _______________ Hydrogen bonds that hold the strands together and unwind it. DNA polymerase joins nucleotides 2. _______________ using original strand as template and spell checks ______________for errors. opposite directions 3. Copying happens in ________ along the two strands & in __________ multiple places at once. REPLICATION ANIMATION See a video clip about DNA REPLICATION