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BIOLOGY CONCEPTS & CONNECTIONS Fourth Edition Neil A. Campbell • Jane B. Reece • Lawrence G. Mitchell • Martha R. Taylor CHAPTER 10 Molecular Biology of the Gene Modules 10.1 – 10.5 From PowerPoint® Lectures for Biology: Concepts & Connections Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Saboteurs Inside Our Cells • The invasion and damage of cells by the herpesvirus can be compared to the actions of a saboteur intent on taking over a factory – The herpesvirus hijacks the host cell’s molecules and organelles to produce new copies of the virus Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Viruses provided some of the earliest evidence that genes are made of DNA • Molecular biology studies how DNA serves as the molecular basis of heredity Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings In 1928, Frederick Griffith, an English army doctor, wanted to make a vaccine against a bacteria named Streptococcus pneumoniae, which caused a type of pneumonia. Since the time of Pasteur, about 50 years before, vaccines had been made using killed microorganisms which could be injected into patients to elicit the immune response of live cells without risk of disease. Though he failed in making the vaccine he stumbled on a demonstration of the transmission of genetic instructions by a process we now call the "transformation principle". Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Experiments showed that DNA is the genetic material Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • What was the transforming principal?????? Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Experiments showed that DNA is the genetic material Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • DNA was the genetic, transforming principal…. Oswald Avery: the professor, DNA, and the Nobel Prize that eluded him. Professor Emeritus of Pathology, Dalhousie University. In 1944, two Canadians, Oswald Avery and Colin MacLeod, and an American, McCarty, published a paper in The Journal of Experimental Medicine that demonstrated genes to be the chemical, deoxyribonucleic acid (DNA). Even though this paper is now regarded as the single most important publication in biology of the 20th century, Avery was not awarded the Nobel Prize. This raises the question as to why his work did not earn him the Prize. These are several possible reasons: the discovery may have been ahead of tis time; all three authors were physician-scientists and not recognized chemists or geneticists; and Avery, the principal author, had reached an advanced age and characteristically took an extremely cautious and low-key approach to his work. Discussion of these reasons in turn raises other issues surrounding the recognition of the work of celebrated scientist, from Galileo and Copernicus onwards. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Experiments showed that DNA is the genetic material • The Hershey-Chase experiment showed that certain viruses reprogram host cells to produce more viruses by injecting their DNA Head DNA Tail Tail fiber Figure 10.1A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Phage reproductive cycle Phage attaches to bacterial cell. Phage injects DNA. Phage DNA directs host cell to make more phage DNA and protein parts. New phages assemble. Cell lyses and releases new phages. Figure 10.1C Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • The Hershey-Chase Experiment 1 Mix radioactively labeled phages with bacteria. The phages infect the bacterial cells. Phage 2 Agitate in a blender to separate phages outside the bacteria from the cells and their contents. Radioactive protein Bacterium 3 Centrifuge the mixture so bacteria form a pellet at the bottom of the test tube. 4 Empty protein shell Measure the radioactivity in the pellet and liquid. Radioactivity in liquid Phage DNA DNA Batch 1 Radioactive protein Centrifuge Pellet Batch 2 Radioactive DNA Radioactive DNA Figure 10.1B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Centrifuge Pellet Radioactivity in pellet For his fundamental contributions to molecular biology, Hershey received the 1958 Albert Lasker Award and the 1965 Kimber Genetics Award. However, it was not until 1969 that Hershey, together with Delbrück and Luria, was awarded the Nobel Prize for physiology or medicine. Martha Chase was a lab assistant in the 1950’s and did not receive the Nobel Prize for her work. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings DNA and RNA are polymers of nucleotides • DNA is a nucleic acid, made of long chains of nucleotides Phosphate group Nitrogenous base Sugar Phosphate group Nitrogenous base (A, G, C, or T) Nucleotide Thymine (T) Sugar (deoxyribose) DNA nucleotide Polynucleotide Sugar-phosphate backbone Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 10.2A • DNA has four kinds of bases, A, T, C, and G Thymine (T) Cytosine (C) Pyrimidines Adenine (A) Guanine (G) Purines Figure 10.2B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Note the designation of the Carbons as 1-5. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 10.3 DNA is a double-stranded helix • James Watson and Francis Crick worked out the three-dimensional structure of DNA, based on work by Rosalind Franklin Figure 10.3A, B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • The structure of DNA consists of two polynucleotide strands wrapped around each other in a double helix 1 chocolate coat, Blind (PRA) Twist Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 10.3C • Hydrogen bonds between bases hold the strands together – Each base pairs with a complementary partner – A pairs with T – G pairs with C Chargaff’s Rule Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Three representations of DNA Hydrogen bond Ribbon model Partial chemical structure Computer model Figure 10.3D Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Z-form A-form right-handed B-form right-handed Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings left-handed DNA REPLICATION 10.4 DNA replication depends on specific base pairing • In DNA replication, the strands separate – Enzymes use each strand as a template to assemble the new strands A Nucleotides Parental molecule of DNA Both parental strands serve as templates Two identical daughter molecules of DNA Figure 10.4A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Untwisting and replication of DNA Figure 10.4B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 10.5 DNA replication: A closer look • DNA replication begins at specific sites Origin of replication Parental strand Daughter strand Bubble Two daughter DNA molecules Figure 10.5A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Tid Bits • 1. If multiple sites were not being replicated simultaneously: – Fruit fly DNA would take 16 days to replicate only 8 chromosomes – In bacteria, 500 nucleotides are being added per second/ eukaryotes are adding 50 nucleotides per second. 2. Replication must take place in a 5’ to 3’ direction and the DNA strand is antiparallel 3. Eukaryotes have directional issues and telomere issues!!! (To be discussed soon, stay tuned) Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Each strand of the double helix is oriented in the opposite direction 5 end 3 end P P • There is only 1 error per billion base pairs!! Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings P Figure 10.5B P P P • Nucleotides can only be added to the free 3’ end of the DNA strand. P P 3 end 5 end • How DNA daughter strands are synthesized DNA polymerase molecule 5 end • The daughter strands are identical to the parent molecule Daughter strand synthesized continuously Parental DNA 5 3 – 5’ – 3’ direction Daughter strand synthesized in pieces 3 5 P 5 3 3 5 P DNA ligase Overall direction of replication Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 10.5C • The Enzymes of DNA Synthesis Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings DNA polymerase I fills in the spaces between the Okasaki Fragments. DNA polymerase III adds nucleotides to the “free 3.” Gyrase unwinds the DNA by catalyzing the formation of negative supercoils. Helicase separates the strands. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings DNA polymerase II is a prokaryotic DNA polymerase most likely involved in DNA repair Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The initial requirement for a free 3' hydroxyl group is fulfilled by the RNA primers that are synthesized at the initiation sites by primase enzymes. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • RNA is also a nucleic acid – RNA has a slightly different sugar – RNA has U instead of T Nitrogenous base (A, G, C, or U) Phosphate group Uracil (U) Sugar (ribose) Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 10.2C, D