18.1 Section Objectives – page 475

1. 18.1 Section Objectives – page 475 Section Objectives: 18.1 • Identify the different kinds of viruses and their structures. • Compare and contrast the replication cycles of viruses.

2. Section 18.1 Summary – pages 475-483 • You’ve probably had the flu—influenza—at some time during your life. • Nonliving particles called _______ cause influenza. • Viruses are composed of _____ ______ enclosed in a ______ coat and are smaller than the smallest bacterium.

3. Section 18.1 Summary – pages 475-483 • Most biologists consider viruses to be _______ because they don’t exhibit all the ______ for life. • They don’t carry out respiration, grow, or develop. All viruses can do is _______—make copies of themselves—and they can’t even do that without the help of living cells. • A cell in which a virus replicates is called the _____cell.

4. Section 18.1 Summary – pages 475-483 • Viruses, such as _____ viruses and _____ viruses, were named after the diseases they cause. • Other viruses were named for the _____ or ______ they infect.

5. Section 18.1 Summary – pages 475-483 • Today, most viruses are given a ______ name ending in the word “virus” and a ______ name. • However, sometimes scientists use ____ numbers to distinguish among similar viruses that infect the same ____. • A virus that infects a bacterium is called a __________ (bak TIHR ee uh fayj), or phage for short.

6. Section 18.1 Summary – pages 475-483 • A virus has an inner core of nucleic acid, either ___ or ___, and an outer protein coat called a ____. Capsid Nucleic acid Envelope

7. Section 18.1 Summary – pages 475-483 • Some relatively large viruses, such as human ___ viruses, may have an additional layer, called an _______, surrounding their capsids. Capsid Nucleic acid Envelope

8. Section 18.1 Summary – pages 475-483 • Envelopes are composed primarily of the same materials found in the ______ membranes of all cells. Capsid Nucleic acid Envelope

9. Section 18.1 Summary – pages 475-483 Nucleic acid • ___ nucleic acid is either DNA or RNA and contains instructions for making copies of the virus. Capsid • Some viruses have only four _____, while others have hundreds.

10. Section 18.1 Summary – pages 475-483 Nucleic acid • The _____ _____ virus has a long, narrow _______ shape. Capsid

11. Section 18.1 Summary – pages 475-483 • The arrangement of _____ in the capsid of a virus determines the virus’s _____. Capsid Nucleic acid • ________ viruses resemble small crystals.

12. Section 18.1 Summary – pages 475-483 • The protein arrangement also plays a role in determining what cell can be _______ and how the virus infects the cell. Nucleic acid Capsid

13. Section 18.1 Summary – pages 475-483 • Before a virus can replicate, it must ____ a host cell. • A virus recognizes and ______ to a host cell when one of its ______ interlocks with a molecular shape that is the ______ site on the host cell’s plasma membrane.

14. Section 18.1 Summary – pages 475-483 • A protein in the ___ fibers of the bacteriophage __ recognizes and attaches the T4 to its bacterial host cell. Capsid Nucleic acid Tail Tail fiber

15. Section 18.1 Summary – pages 475-483 Capsid • In other viruses, the attachment protein is in the ____ or in the envelope. Nucleic acid Tail Tail fiber

16. Section 18.1 Summary – pages 475-483 • Each virus has a ________ shaped attachment protein. Therefore, each virus can usually attach to only a few kinds of cells. • In general, viruses are species specific, and some also are ____-type specific. For example, polio viruses normally infect only intestinal and nerve cells.

17. Section 18.1 Summary – pages 475-483 • The species specific characteristic of viruses is significant for controlling the spread of _____ diseases.

18. Section 18.1 Summary – pages 475-483 • Once attached to the plasma membrane of the host cell, the virus _____ the cell and takes over its ________. • Only then can the virus ________. • Viruses have ____ways of getting into host cells.

19. Section 18.1 Summary – pages 475-483 • The virus may _____its nucleic acid into the host cell like a syringe injects a vaccine into your arm. • The _____ of the virus stays attached to the outside of the host cell. • An ________ virus enters a host cell in a different way.

20. Section 18.1 Summary – pages 475-483 • After attachment, the plasma membrane of the host cell surrounds the virus and produces a virus-filled vacuole inside the host cell’s cytoplasm. • Then, the virus bursts out of the vacuole and releases its nucleic acid into the cell.

21. Section 18.1 Summary – pages 475-483 • Once inside the host cell, a virus’s genes are _________ and the substances that are produced take over the host cell’s genetic material. • The ____ genes alter the host cell to make new viruses.

22. Section 18.1 Summary – pages 475-483 Bacteriophage Bacterial DNA Nucleic acid Bacterial host cell B. Entry A. Attachment The bacteriophage injects its nucleic acid into the bacterial cell. E. Lysis and Release The host cell breaks open and releases new virus particles. C. Replication D. Assembly The host’s metabolic machinery makes viral nucleic acid and proteins. New virus particles are assembled.

23. Section 18.1 Summary – pages 475-483 • The host cell uses its own _______, raw materials, and energy to make copies of viral genes that along with viral proteins are assembled into new viruses, which _____ from the host cell, killing it.

24. Section 18.1 Summary – pages 475-483 • The new viruses can then infect and kill other host cells. This process is called a ____ (LIH tik) _____.

25. Section 18.1 Summary – pages 475-483 • Not all viruses ____ the cells they infect. • Some viruses go through a ________ cycle, a replication cycle in which the virus’s nucleic acid is ________ into the host cell’s chromosome.

26. Section 18.1 Summary – pages 475-483 • A ________ cycle begins in the same way as a lytic cycle. • However, in a lysogenic cycle, instead of _________ taking over the host’s genetic material, the viral DNA is integrated into the host cell’s chromosome.

27. Section 18.1 Summary – pages 475-483 • Many disease-causing ______ have lysogenic cycles. • Three examples of these viruses are ____ _____ I, herpes simplex II that causes ______ herpes, and the _______ B virus that causes hepatitis B.

28. Section 18.1 Summary – pages 475-483 • Another lysogenic virus is the one that causes _____ ___.

29. Section 18.1 Summary – pages 475-483 • Having chicken pox, which usually occurs before age ten, gives lifelong protection from another infection by the ___. However, some chicken pox viruses may remain as _________ in some of your body’s nerve cells.

30. Section 18.1 Summary – pages 475-483 • Later in your life, these proviruses may enter a lytic cycle and cause a disease called _______—a painful infection of some nerve cells.

31. Section 18.1 Summary – pages 475-483 • Either lysis, the bursting of a cell, or ______, the active transport process by which materials are expelled from a cell, release new viruses from the host cell.

32. Section 18.1 Summary – pages 475-483 • In exocytosis, a newly produced virus approaches the inner surface of the host cell’s _______ membrane. • The plasma membrane surrounds the virus, enclosing it in a _____ that then fuses with the host cell’s plasma membrane. • Then, the ______are released to the outside.

33. Section 18.1 Summary – pages 475-483 • Many viruses, such as the _____ _______________ ____(HIV) that causes the disease AIDS, are RNA viruses—RNA being their only nucleic acid. HIV virus

34. Section 18.1 Summary – pages 475-483 • Once inside a human host, HIV infects _____ blood cells. Normal white blood cells • Newly made viruses are released into the blood stream by ________ and infect other white blood cells.

35. Section 18.1 Summary – pages 475-483 • Infected host cells still function normally because the viral genetic material is a ______ that produces only a small number of new viruses at a time. • Because the infected cells are still able to function normally, an infected person may not appear _____, but they can still ____ the virus in their body fluids.

36. Section 18.1 Summary – pages 475-483 • Most people with an HIV infection eventually get ____ because, over time, more white blood cells are infected and produce new viruses. • Because white blood cells are part of a body’s ______-fighting system, their destruction interferes with the body’s ability to protect itself from organisms that cause disease, a symptom of AIDS.

37. Section 18.1 Summary – pages 475-483 • Some viruses have been linked to certain ______ in humans and animals. • These viruses disrupt the normal growth and division of cells in a host, causing abnormal growth and creating _______.

38. Section 18.1 Summary – pages 475-483 • Researchers have recently discovered some particles that behave somewhat like viruses and cause infectious diseases. • Prions are composed of proteins but have no nucleic acid to carry genetic information.

39. Section 18.1 Summary – pages 475-483 • Prions are thought to act by causing other proteins to fold themselves incorrectly, resulting in improper functioning. • Prions are responsible for many animal diseases, such as mad cow disease and its human equivalent, Creutzfeldt-Jakob disease.

40. Section 18.1 Summary – pages 475-483 • Viroids are composed of a single circular strand of RNA with no protein coat. • Viroids have been shown to cause infectious diseases in several plants. • The amount of viroid RNA is much less than the amount found in viruses.

41. Section 18.1 Summary – pages 475-483 • The first virus to be identified was a plant virus, called tobacco mosaic virus, that causes disease in tobacco plants. Tobacco mosaic virus causes yellow spots on tobacco leaves, making them unmarketable.

42. Section 18.1 Summary – pages 475-483 • Viruses cause as many as 1000 plant diseases and are named according to their host plant. • Viruses can cause stunted growth and yield losses in their host plants.

43. Section 18.1 Summary – pages 475-483 • Plant viruses require wounds or insect bites to enter and infect a host, and do not use surface recognition. • They do not undergo lytic or lysogenic phases.

44. Section 18.1 Summary – pages 475-483 • Not all viral plant diseases are fatal or even harmful. • Some mosaic viruses cause striking patterns of color in the flowers of plants. Rembrandt tulips

45. Section 18.1 Summary – pages 475-483 • For replication, viruses need host cells; therefore, scientists suggest that viruses might have originated from their host cells. • Some scientists suggest that viruses are nucleic acids that break free from their host cells while maintaining an ability to replicate parasitically within the host cells.

46. Section 2 Objectives – page 484 Section Objectives 18.2 • Compare the types of prokaryotes. • Explain the characteristics and adaptations of bacteria. • Evaluate the economic importance of bacteria.

47. Section 18.2 Summary – pages 484-495 • Recall that prokaryotes are _________ organisms that do not have a nucleus or membrane-bound organelles. • They are classified in two kingdoms— _________ and ________. • Many _________ differences exist between these two types of prokaryotes.

48. Section 18.2 Summary – pages 484-495 • Because they are so different, many scientists propose that archaebacteria and eubacteria arose from a _______ ancestor several billion years ago.

49. Section 18.2 Summary – pages 484-495 • There are ____ types of archaebacteria that live mainly in extreme habitats where there is usually no free ______ available. • One type of archaebacterium lives in oxygen-free environments and produces ______ gas.

50. Section 18.2 Summary – pages 484-495 • These methane-producing archaebacteria live in marshes, lake sediments, and the digestive tracts of some ________, such as cows.