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Bio 1010 Dr. Bonnie A. Bain CHAPTER 10 DNA Structure and Function Part 3 Viruses Don't Forget: Exam 3 November 21 Bring Scantron and #2 Pencil Point Mutations: A change in a single nucleotide Frameshift Mutations: An insertion or deletion of 1 or 2 nucleotides Remember: Mutations are the ultimate source of diversity of life on our planet Figure 10.23 Figure 10.24 Viruses: Genes in Packages Why talk about viruses here? Answer: Virus is “DNA in a Box” A Virus consists of a protein coat (the box) plus either a strand of DNA or RNA Fig. 10-24 Protein coat DNA Characteristics of Viruses 1. Has genes (DNA or RNA) 2. Reproduces by infecting other cells and hijacking their molecular machinery to make more viruses 3. Has a complex structure Figure 10.24 Adenovirus These cause respiratory infections in humans Figure 10.25 Bacteriophage 200 nm high or 0.0002 mm Infect Bacteria Fig. 10-26c Phage lambda E. coli Bacteriophage Reproduction 1. Inject their DNA into the “host” bacterium 2. The injected DNA forms a circle. The circle of DNA then hijacks the cell's machinery and makes lots more copies of itself as well as copies of the protein coat “parts” 3. New phages are assembled and then leave the bacterium (by lysing it, usually) Fig. 10-26-2 Phage Phage attaches to cell. Cell lyses, releasing phages. Phage DNA Bacterial chromosome (DNA) Phage injects DNA Many cell divisions Occasionally a prophage may leave the bacterial chromosome. LYTIC CYCLE Phages assemble Phage DNA circularizes. LYSOGENIC CYCLE Prophage Lysogenic bacterium reproduces normally, replicating the prophage at each cell division. OR New phage DNA and proteins are synthesized. Phage DNA is inserted into the bacterial chromosome. Bacteriophage Life Cycles Lytic Cycle – After lots of viral copies made, – they escape the cell by lysing it – (breaking it open) Lysogenic Cycle – Viral DNA replication occurs, – but no phage are produced – and the cell doesn't die Figure 10.28 Influenza Virus Causes the Flu Figure 10.30a Question: Are viruses alive?? Characteristics of living organisms (page 4): 1. Organization and complexity 2. Regulation (physiology) 3. Growth and development 4. Utilize Energy 5. Respond to environment 6. Reproduce 7. Evolve (change over time) How are viruses related to living organisms?? Figure 14.26 Origin of viruses 1. Regressive Theory: Viruses originated from bacteria that became intracellular parasites These became dependent upon a host Then lost most of their genetic information Origin of Viruses 2. Run-away RNA: Viruses arose from host RNA or DNA that gained a self-replicative, but parasitic existence and acquired the ability to replicate independently of their host Origin of Viruses 3. Co-evolution: Viruses originated and evolved along with the most primitive molecules (the first ones able to self-replicate) Some molecules were packaged into membranes and eventually became cells Others became packaged into protein coats and became virus particles that co-evolved with cells and parasitized them Many Viruses cause disease Animal viruses: Adenovirus HIV Ebola Polio Mumps West Nile Avian flu SARS Etc. Many Viruses cause disease Plant Viruses: Tobacco Mosaic virus infects lots of agricultural crops (tomato, squash, cantaloupe, etc.) Papaya ringspot potyvirus (PRSV) Kills papaya plants Fig. 10-27 RNA Protein Tobacco mosaic virus Treatment of Viruses Very hard to treat viral diseases Antibiotics do NOT work on viral infections (only work on bacteria) Treatment of Viruses Many treatments that kill viruses will also kill the host Antiviral Drugs: Some focus on enzymes that the virus uses High mutation rates in viruses Best treatments are vaccinations Your own immune system attacks viruses on contact Figure 10.29 Mumps Virus Life Cycle (p. 191) Virus Life Cycle (Enveloped RNA virus) This type of virus has RNA covered with protein First, the virus attaches to the cell with its protein spikes Virus Life Cycle (Enveloped RNA virus) Then: 1. Viral envelope fuses with cell membrane; allowing the viral RNA to enter the cytoplasm 2. Enzymes remove the protein covering around the viral RNA 3. Using the viral RNA as a template, a viral enzyme makes copies of the viral RNA Figure 10.29 Mumps Virus Life Cycle (p. 191) Virus Life Cycle (Enveloped RNA virus) 4. Two functions for the viral RNA copies: a. Act as mRNA to make new viral proteins (using the host cell's ribosomes) b. Act as templates for making more virus RNA Virus Life Cycle (Enveloped RNA virus) 5. The newly made viral proteins assemble around the newly made copies of the virus RNA, forming lots more new viruses 6. The new virus copies leave the cell Figure 10.29 Mumps Virus Life Cycle (p. 191) Lots of variations on the viral life cycle Viruses can replicate in the nucleus or the cytoplasm of the host cell Some viruses (Herpes simplex 1, 2; Polio virus) replicate inside nerve cells only Lots of variations on the viral life cycle Some are DNA viruses Some are RNA viruses Some reproduce like the Mumps virus Others use Reverse Transcriptase (HIV virus) Figure 10.30c HIV virus Causes AIDS Life Cycle: 1. Virus attaches to a white blood cell (T cell) and injects its RNA into the cell 2. The viral enzyme, Reverse Transcriptase, makes two copies of DNA using the RNA as a template Figure 10.30a HIV virus life cycle (con't) 3. The newly made viral DNA goes into the nucleus and inserts itself into the host cell's DNA 4. This is then transcribed and the mRNA is used to make new viral proteins (using the cell's ribosomes) 5. Newly formed viral particles leave the cell 7. Viruses bud from host cell 1. Attachment 2. Penetration 6. Viral proteins and RNA assembled into new virus 3. Viral RNA to Viral DNA 4. Viral DNA incorporated into host DNA 5. Viral proteins and RNA synthesized by host cell Figure 10.00a Anti-HIV Drugs 1. AZT Function: inhibits Reverse Transcriptase 2. Protease Inhibitors Function: block the formation of the HIV viral proteins This “drug cocktail” keeps the virus in check and extends people's lives, but it is NOT A CURE Figure 10.1 How AZT works Next Chapter: Chapter 11 How Genes are Controlled (Gene Regulation) Don't Forget: Exam 3 November 21 Bring Scantron and #2 Pencil