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DNA Chapter 2 – read principal points TimelineTimeline for genetics
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Deoxyribonucleic acid Functional Properties 1. Replication – DNA is copied prior to cell division why?
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2. Storage of information DNA inherited from parent to offspring from cell to cell Gene expression – Genes encode proteins 3. Mutation – DNA changes to allow variation and adaptation, the basis of evolution
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A six-legged green frog. (Reproduced by permission of JLM Visuals http://www.isogenic.info/assets/images/autogen/a_image16.jpg http://3quarksdaily.blogs.com/3quarksdaily/images/wolfe_seal_1.jpg Neutral, harmful, adaptive?
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DNA History 1869 Meischer extracted nuclein from pus 1900s – chromosomes discovered The genetic material must have the 3 functional properties microscopy.bio.cmich.edu
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Griffith finds “transforming factor” 1928 London Streptococcus pneumoniae bacterium pneumonia in mice, deadly to humans sputum with bacteria
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Smooth strain (IIIS) virulent polysaccharide capsule capsule allows bacteria to evade immune system Fluorescent stain of capsule
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isolate live IIIS from mouse
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S pneumococcus kills mouse in 24 hours. But 100 million IIR strain bacterial cells is harmless SRSR (Research photographs of Dr. Harriet Ephrussi-Taylor, courtesy of The Rockefeller University.) Appearance when grown on an agar plate
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http://biology.kenyon.edu/courses/biol114/KH_lecture_images/How_DNA_works/how_ DNA-works.html
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Rough strain IIR is avirulent IIR lacks capsule -> isolate live IIR
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The experiment: Heat kill IIIS strain mouse ?
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Heat killed IIIS strain + live strain IIR mouse ? Which strain is isolated?
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Griffith’s experiment and conclusion A “transforming factor” in killed S strain transformed live R strain into S DNA or protein?
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1944 Avery, McCarty, Macleod 1. Heat kill IIIS 2. Remove lipids and sugars – how? FYI iGenetics: DNA as Genetic Material: Avery’s Transformation Experiment
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3. Divide into 3 and treat with: protease RNase DNase next, add live R cells to each
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1952 Hershey and Chase Used T2 bacteriophage + E. coli A phage is a virus that infects bacteria
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How phage work 1. phage adsorbs onto bacterial surface 2. Genetic material injected 3. Cell makes progeny phage IS the genetic material DNA, or protein?
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Experiment 1. Label phage protein with 35 S infect E. coli strip phage off cell surface New phage are not radioactive
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2. Label phage DNA with 32 P -> infect E.coli -> blend -> New phage contain 32 P
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http://osulibrary.orst.edu/specialcollections/coll/pauling/dna/pictures/hersheych ase-experiment.html
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Hershey and Chase conclusion DNA is responsible for function and reproduction of phage virus = the genetic material
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Structure of DNA = nucleotide polymers NUCLEOTIDES 1. Nitrogenous base Purines = guanine and adenine G A Purines attached to 1 carbon of sugar at 9 nitrogen, covalent bond, pyrimidines attached to 1 carbon at 1 nitrogen How big IS a nucleotide? UTAH cell scale
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Pyrimidines Thymine T Cytosine C RNA contains uracil U
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2. Deoxyribose sugar RNA (ribose) 2’ OH makes RNA less stable than DNA Sugar + base = nucleoside
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3. Phosphate (PO 4 ) Nucleotide = base + sugar + phosphate Phosphate covalently (phosphodietster bond) attached to 5’C of sugar Phosphodiester bond - Covalent bond between phosphate of one nucleotide and 3’ sugar carbon of another 9 N (purine) or 6N (pyrimidine) covalently bonded to 1C of sugar
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DNA is a polymer of nucleotides polarity 5’carbon to 3’hydroxyl
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DNA (double helix) Watson and Crick 1953 X-ray diffraction data Rosalind Franklin, Maurice Wilkins
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DNA properties include:
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Complementary base pairing 1. Hydrogen bonds between complementary bases How many bonds in a G-C pair? A-T? Which is stronger?
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Complementary base pairs Which are the G-C pairs?
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2. antiparallel stands 5’ 3’ and 3’ 5’
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3. Sugar phosphate backbones
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4. Base composition DNA 50% purine 50% pyrimidine A = TG = C A/T = 1C/G = 1 A +T does not equal C+G A + G = C + T Chargaff (1950)
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5. DNA can denature and renature Melt hydrogen bonds (chemical or heat)
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And 5. Right handed helix 6. Complete turn of the helix is 0.34 nm, 10 bases per turn 7. Major and minor grooves
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Major and minor grooves
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Forms of DNA B DNA right helix 10 bp/ turn A DNA right helix 10.9 bp/ turn Z DNA left helix 12 bp/turn (role?) Cellular DNA closest to B DNA 10.4 bp/turn
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Replication of DNA by Complementary Base Pairing HHMI interactive DNA replicationHHMI interactive DNA replication advanced
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Organization of DNA in chromosomes Genome Full amount of genetic material in a single cell
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Influenza ssRNAHIV ssRNA Bacteriophage ds DNA Viral chromosome Single or double stranded DNA or RNA Circular or linear Herpes ds DNA Parvovirus ssDNA
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Genetic material in prokaryotes 1 (usually) chromosome Circular (most) chromosome Supercoiled DNA located in nucleoid region Neisseria gonorrhoeae
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E. coli = 4.6 million bp, circular chromosome 1500 um genome stuffed into a 1 um cell via supercoiling E. Coli cellsE. coli DNA map of chromosome
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Some bacteria contain extra-chromosomal DNA called a plasmid
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Eukaryotic Chromosomes C value - Amount of DNA varies among species
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The structure of chromatin DNA + proteins Highly conserved
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Histones and non-histones Histone proteins basic net + charge interacts with – charged DNA Package DNA Highly conserved Non-histone proteins vary among species http://faculty.jsd.claremont.edu/jarmstrong/images/chromatin.gif
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What do histones do? 1. pack DNA into chromatin Condense DNA 10,000X (2 meters nanometers) 1. Modifications to histone proteins affect gene expression
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5 histone proteins Histone type #amino acidscontent_________________ H1 200-26527%lysine, 2%arginine H2A 129-155 11% lysine, 9% arginine H2B 121-155 6% lysine, 6% arginine H3 135 10%lysine, 15% arginine H4 102 11% lysine, 4% arginine Note: all are lysine/arginine rich, they contain other amino acids, but at small percentages. Basic, + charge
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Gel electrophoresis
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epigenetics Modification of histone proteins changes gene expression. Chemical tags can be inherited and are stable in cell division
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Pbs: A Tale of Two Mice Pbs: A Tale of Two Mice Epigenetics with deGrassi http://www.pbs.org/wgbh/nova/scienceno w/3411/02.html http://www.pbs.org/wgbh/nova/scienceno w/3411/02.html Agouti Mice Epigenetics and gene silencing Mouse and twin studies Diet and the epigenome Methyl group tags
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Chromosome packaging 1. Nucleosomes 1 nucleosome “beads on a string” The 10 um chromatin fiber 2(H2A).2(H2B) 2(H3).2(H4) octomer
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Dual role of nucleosomes stable to shelter DNA and compact it labile to allow DNA information to be used
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2. The 30 nm chromatin fiber Histone H1 a ttaches linker DNA to nucleosomes
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The 30 nm chromatin fiber (11nm string-> 30 nm helical fiber) See Science article
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3. Further packaging into loops and scaffolds……
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Summary of DNA packaging 30nm chromatin fiber Nucleosomes DNA helix
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Metaphase chromosome is 10,000 X condensed compared to double helix Condensed scaffold The scaffold with loops
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Euchromatin and Heterochromatin
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1. Heterochromatin Condensed Transcriptionally inactive Ex. centromeres
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Heterochromatin stains darkly
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Heterchromatin example Barr body (facultative, extent of inactivity varies) Inactivated X chromosome in females
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2. Euchromatin Lighter staining regions of DNA that contain genes Transcriptionally active
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Unique Sequences and Repetitive DNA
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What genes are on a chromosome? http://www.dnalc.org/ddnalc/resources/chr11.html Chromosome 11 flyover Terms: Transposon Pseudogene Olfactory Polymorphism
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1. Unique Sequence DNA (1 to a few copies) a. Genes Encode proteins ~60% of DNA Only 2% of DNA is coding (H. sapiens) Estimated 20,000 genes in humans
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b. Gene families encodes embryonic beta globin encode fetal beta globin is a pseudogene (not functional) encodes normal beta globin encodes normal adult beta globin Example: Beta globin (encode subunits of hemoglobin)
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2. Repetitive DNA Repeated 10 – 1000sX in the genome a. Dispersed repeated DNA LINES = long interspersed elements 1000 – 7000 bp Ex. humans have 500,000 copies of L1 = 15 % of genome. some are transposons = copy and move
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SINES 100 – 400 bp Ex. Alu repeats repeated 1 million times = 10% of genome
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b. Tandem repeats 1 – 10 bp long tandemly repeated Centromeres, telomeres, rRNA genes Ex. telomere sequence repeated 2000X 5'...TTAGGG TTAGGG TTAGGG TTAGGG TTAGGG TTAGGG..3' 3'...AATCCC AATCCC AATCCC AATCCC AATCCC AATCCC..5'
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Ex. rRNA genes
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