Download Viruses and Evolution Student Recording Sheet

Student Name: __________________________ Viruses and Evolution Student Recording Sheet 1 Viruses and Evolution, Part 1 1. What natural processes have shaped viruses? Natural selection Evolution 2. What are the three parts of a pathogen’s “job”? a. evade the host’s immune system b. make copies of itself c. spread to other hosts 3. Briefly, what is one way that hosts protect themselves from a pathogen such as a virus? They produce antibodies that attach to viral surface proteins. 4. What may happen to a viral lineage if the viruses kill their hosts? They may become extinct. 5. How do viruses adapt to a host’s immunity? Viruses adapt to hosts with constantly changing surface proteins. 6. What is the advantage of constantly changing viral surface proteins? The host has no antibodies for viruses that look different. Viruses and Evolution © 2014 The College of Physicians of Philadelphia page 1 Student Name: __________________________ Viruses and Evolution Student Recording Sheet 2 Web Article: Evolution from a Virus’s View 1. How would a virus describe itself? as part of a rapidly evolving population of organisms that inhabit the bodies of living things such as humans 2. How would a virus describe its pathogenic characteristics that make destroy our cells and make us feel sick? as adaptations, or characteristics favored by natural selection 3. Name four transmission strategies viruses have developed for escaping a host’s immune system. a. airborne transmission b. vector transmission c. waterborne transmission d. sit-­‐and-­‐wait transmission 4. What is the evolutionary trade-­‐off between virulence and transmission? A high level of virulence reduces the chances of transmission because the host is dead or too sick to interact with other hosts. Low levels of virulence increase the chances of transmission because the host is not too sick to go about its business, interacting with many new hosts in the process. 5. Why, from an evolutionary standpoint, did improving sanitation reduce the virulence of the cholera pathogen? Improving sanitation cuts off the main pathway of rapid cholera transmission. The less virulent pathogens become the most likely ones to be transmitted and to reproduce. Viruses and Evolution © 2014 The College of Physicians of Philadelphia page 2 Student Name: __________________________ Viruses and Evolution Student Recording Sheet 3 Web Article: HIV: The Ultimate Evolver 1. What may be the way to control the spread of the human immunodeficiency virus, or HIV? Controlling the evolution of HIV may be the way to control this constantly adapting virus. 2. What two factors contribute to the fact that HIV is one of the fastest evolving entities known? a. It reproduces in a way that allows lots of mutations to accumulate. b. It reproduces at a lightning-­‐fast rate. 3. Which other viruses is HIV closely related to? SIVs, simian immunodeficiency viruses, and FIVs, feline immunodeficiency viruses 4. What is an important difference between HIV infections and SIV and FIV infections? Non-­‐human primates and wild cats live with the viruses, unlike humans with HIV 5. What is CCR5? CCR5 is a remnant of human evolutionary battles with pathogens that has given researchers hope of developing new treatments for HIV infections. 6. Where is the protective mutant CCR5 allele most prevalent and least prevalent? Mutant CCR5 is most prevalent in Europe and least prevalent in Africa. 7. Why does treatment for HIV involve the use of “drug cocktails”? Drug resistant strains evolve rapidly during treatment with a single drug. Viruses and Evolution © 2014 The College of Physicians of Philadelphia page 3 Student Name: __________________________ Viruses and Evolution Student Recording Sheet 5 Viruses and Evolution, Part 2 8. How are influenza viruses and HIV similar? Both are RNA viruses. 9. Are DNA viruses or RNA viruses more stable and less likely to evolve new forms through mutation? Explain. DNA viruses; they have a proofreading check that corrects errors made during replication and can also use a host cell’s error correction system 10. Why do RNA viruses evolve so quickly? RNA is less stable, so it mutates more often, and RNA viruses have no systems for proofreading mistakes made in copying RNA. 11. What is the basic structure of an influenza virus? It consists of 7 or 8 segments of RNA surrounded by a protein envelope. 12. What causes evolution in influenza viruses? Mutations in RNA and recombinations of RNA from different sources both cause evolution of influenza viruses. ANTIGENIC DRIFT: 13. What are HA and NA? HA stands for hemagglutinin. NA stands for neuraminidase. Both are viral surface proteins encoded by viral genes that mutate often. 14. What does the designation H1N1 refer to? H refers to HA, or hemagglutinin. N refers to NA, or neuraminidase. The 1 digits refer to versions of these surface proteins that result from mutations of the RNA code for the proteins. Viruses and Evolution © 2014 The College of Physicians of Philadelphia page 4 ANTIGENIC SHIFT: 15. What are the three main types of influenza viruses? The main types of influenza viruses are A, B, and C strains. 16. Which type of influenza virus evolves through antigenic shift? What is the key to its ability to do so? Only A strains evolve through antigenic shift. They are able to do so because they infect many different kinds of animals, including birds, pigs, and humans. Recombination possibilities with Influenza B and C viruses are very limited. 17. Describe the two ways in which antigenic shift occurs. a. One way is by genetic recombination. This happens when two or more different influenza viruses such as a pig virus and a human virus infect the same cell. As the viral particles are reproduced, reassortment of the RNA strands from the two strains produces new strains very different from the original one. b. Another way is by one viral strain jumping from one kind of animal such as a bird to individuals of different species without undergoing any genetic change. If the virus can reproduce and infect other cells, it will be able to mutate. If some of the mutants are easily able to spread to other humans, a pandemic can result. 18. Why didn’t the 2003 outbreak of bird flu become a pandemic? A strain of the H5N1 influenza A virus that was easily spread among humans has never evolved. Viruses and Evolution © 2014 The College of Physicians of Philadelphia page 5