1. BIOLOGY CONCEPTS & CONNECTIONS Fourth Edition Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Neil A. Campbell Jane B. Reece Lawrence G. Mitchell Martha R. Taylor From PowerPoint ® Lectures for Biology: Concepts & Connections CHAPTER 10 Molecular Biology of the Gene Modules 10.17 – 10.22

2. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings VIRUSES: GENES IN PACKAGES The Molecular Genetics of Viruses Viral DNA may become part of the host chromosome Phage New phage DNA and proteins are synthesized Phage DNA inserts into the bacterial chromosome by recombination Attaches to cell Phage DNA Bacterial chromosome Phage injects DNA Occasionally a prophage may leave the bacterial chromosome Many cell divisions Lysogenic bacterium reproduces normally, replicating the prophage at each cell division Prophage Phage DNA circularizes LYSOGENIC CYCLE Cell lyses, releasing phages Phages assemble LYTIC CYCLE OR

3. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Translation of viral genes in Prokaryotes Prophage genes inserted in the DNA of essentially harmless bacteria cause botulism, diptheria, and scarlet fever. This occurs when prophage genes become active in the host genome. Also, an environmental signal such as radiation or a certain chemical triggers a switchover from the lysogenic cycle to the lytic cycle.

4. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Many viruses have RNA, rather than DNA, as their genetic material RNA viruses include: flu, cold, measles, mumps as well as AIDS and polio. DNA viruses include: hepatitis, chicken pox, herpes Not all viruses reproduce in the cytoplasm, some like herpes reproduce in the nucleus. 10.18 Connection: Many viruses cause disease in animals Figure 10.18A Membranous envelope RNA Protein coat Glycoprotein spike

5. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Viral Classification 20 - 300 nm, origin not clear because ther is no fossil record. The smallest genomes code for only four proteins and weigh about 106 daltons, while the largest weigh about 108 daltons and code for over one hundred proteins.nmdaltons Baltimore Classification IdsDNA virusesdsDNA viruses IIssDNA virusesssDNA viruses IIIdsRNA virusesdsRNA viruses IV(+)ssRNA viruses(+)ssRNA viruses V(-)ssRNA viruses(-)ssRNA viruses VIssRNA-RT virusesssRNA-RT viruses VIIdsDNA-RT virusesdsDNA-RT viruses ss: single-stranded ds: double stranded RT: reverse transcribing

6. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings In taxonomy, the classification of viruses is rather difficult due to the lack of a fossil record and the dispute over whether they are living or non-living. They do not fit easily into any of the domains of biological classification and therefore classification begins at the family rank. However, the domain name of Acytota (without cells) has been suggested. This would place viruses on a par with the other domains of Eubacteria, Archaea, and Eukarya. Not all families are currently classified into orders, nor all genera classified into families.taxonomydomains biological classification familyAcytotaEubacteriaArchaeaEukarya.

7. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings As an example of viral classification, the chicken pox virus belongs to family Herpesviridae, subfamily Alphaherpesvirinae and genus Varicellovirus. It remains unranked in terms of order. The general structure is as follows:chicken poxHerpesviridae AlphaherpesvirinaeVaricellovirus OrderOrder (-virales) FamilyFamily (-viridae) SubfamilySubfamily (-virinae) GenusGenus (-virus) SpeciesSpecies (-virus) The International Committee on Taxonomy of Viruses (ICTV) developed the current classification system.International Committee on Taxonomy of Viruses

8. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Some animal viruses steal a bit of the host cell’s membrane (Herpes virus) Some remain latent unless cell is stressed How quickly we fight them off with our immune system and how quickly our cells go through mitosis is a factor in how and IF we recover 100% from a viral infection. Figure 10.18B VIRUS Glycoprotein spike Protein coat Envelope Viral RNA (genome) 1 Plasma membrane of host cell Entry 2 Uncoating Viral RNA (genome) 3 RNA synthesis by viral enzyme 4 Protein synthesis 5 RNA synthesis (other strand) mRNA New viral protein New viral proteins 6 Assembly 7 Exit Template New viral genome

9. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Most plant viruses have RNA –Example: tobacco mosaic disease –These viruses enter damaged plants and spread through the plasmodesmata 10.19 Connection: Plant viruses are serious agricultural pests Figure 10.19 ProteinRNA

10. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The deadly Ebola virus causes hemorrhagic fever (1976, Africa) –Each virus is an enveloped thread of protein-coated RNA Hantavirus is another enveloped RNA virus caused by a virus infecting rodents (1993) Viral Encephalitis-inflammation of the brain West Nile (1999-48 states by 2004) SARS (severe acute respiratory syndrome) (China 2003-3months 8,450 infected) 10.20 Connection: Emerging viruses threaten human health Figure 10.20A, B

11. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings HIV is a retrovirus using reverse transcriptase to make a DNA copy of its genome. 10.21 The AIDS virus makes DNA on an RNA template Figure 10.21A Envelope Glycoprotein Protein coat RNA (two identical strands) Reverse transcriptase

12. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Inside a cell, HIV uses its RNA as a template for making DNA to insert into the host chromosome Figure 10.21B Viral RNA 1 2 3 5 4 6 DNA strand Double- stranded DNA Viral RNA and proteins CYTOPLASM NUCLEUS Chromosomal DNA Provirus DNA RNA

13. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Spread of Lethal viruses Viral disease can go from a small population to an epidemic or even pandemic Lethal viruses are more threatening due to biological and technological factors: international travel, blood transfusions, sexual promiscuity, IV drug abuse, jumping the “species barrier”

14. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Bacteria replicate through binary fission Bacteria can transfer DNA in three ways –Bacteria can transfer genes from cell to cell by one of three processes Transformation, transduction, or conjugation DNA enters cell Fragment of DNA from another bacterial cell Bacterial chromosome (DNA ) Phage Fragment of DNA from another bacterial cell (former phage host) Phage Sex pili Mating bridge Donor cell (“male”) Recipient cell (“female”) The Molecular Genetics of the Simplest Living Organisms

15. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings –Once new DNA gets into a bacterial cell Part of it may then integrate into the recipient’s chromosome Recipient cell’s chromosome Recombinant chromosome Donated DNA Crossovers Degraded DNA Figure 10.22D

16. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 10.23 Bacterial F factors and plasmids can serve as carriers for gene transfer F Factor (fertility) is integrated into the host genome Plasmids are not integrated Are small circular DNA molecules separate from the bacterial chromosome Confers antibiotic resistence The ability of E.coli to carry out conjugation

17. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings –Plasmids can serve as carriers For the transfer of genes Plasmids Colorized TEM 2,000  Cell now male Plasmid completes transfer and circularizes F factor starts replication and transfer Male (donor) cell Bacterial chromosome F factor (plasmid) Recombination can occur. Cell still female Only part of the chromosome transfers F factor starts replication and transfer of chromosome Origin of F replication Bacterial chromosome Male (donor) cell F factor (integrated) Recipient cell Figure 10.23A–C

18. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Virus studies help establish molecular genetics Molecular genetics helps us understand viruses –such as HIV, seen here attacking a white blood cell 10.22 Virus research and molecular genetics are intertwined Figure 10.22