Ch 18 Viruses and Bacteria 04 Biology 2008 From Mrs. C. Phillips, DHS black

Ch 18.1 Viruses What kinds of diseases are caused by viruses? Measles Mumps Rubella Chicken pox Polio Cold sores Herpes Rabies Flu Cold HIV Viral pneumonia Hepatitis Mono (if caused by Epstein-Barr virus)

What kingdom do viruses belong to? None- they are not alive!! They are nonliving particles that cause disease pathogens: agents that cause disease Characteristics: –1/2 -1/100 the size of the smallest bacteria –Do not grow, respire, metabolize, develop, respire, maintain homeostasis –Do not have scientific names (named for the disease or tissue they infect) Ex: adenovirus (cold virus) infects adenoid tissue

Viral Structure A virus has an inner core of nucleic acid, either RNA or DNA, and an outer protein coat called a capsid. Capsid Nucleic acid Envelope Some relatively large viruses may have an additional layer, called an envelope, surrounding their capsids. Viral Structure 1

Section 18.1 Summary – pages The arrangement of proteins in the capsid of a virus determines the virus’s shape. Nucleic acid Capsid Polyhedral viruses resemble small crystals.

The tobacco mosaic virus has a long, narrow helical shape. Nucleic acid Capsid

Replication of Viruses There are two ways in which a virus can repilcate: 1. Lytic Cycle and 2. Lysogenic Cycle Each cycle first involves attachment to the host cell. Section 18.1 Summary – pages

Attachment A virus recognizes and attaches to a host cell when one of its proteins interlocks with a molecular shape that is the receptor site on the host cell’s plasma membrane. Viruses are specific to only certain types of cells.

Host specificity The T4 bacteriophage can only infect E. Coli cells. HIV can only infect certain white blood cells. Polio can only infect intestinal and nerve cells. Capsid Nucleic acid Tail Tail fiber

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

Lysogenic Cycle LYSOGENIC CYCLE LYTIC CYCLE The provirus leaves the chromosome. Viral nucleic acid and proteins are made. The cell breaks open releasing viruses. A lysogenic virus injects its nucleic acid into a bacterium. Bacterial host chromosome A. Attachment and Entry B. Provirus Formation Provirus The viral nucleic acid is called a provirus when it becomes part of the host’s chromosome. C. Cell Division Although the provirus is inactive, it replicates along with the host cell’s chromosome. Lysogenic Cycle

Either lysis, the bursting of a cell, or exocytosis, the active transport process by which materials are expelled from a cell, release new viruses from the host cell. Release of Viruses

Retroviruses Have RNA as their nucleic acid Once inside cell, the RNA is turned into DNA by a process called reverse transcription HIV virus

Reverse Transciption This requires the enzyme reverse transcriptase which is carried along in the virus. Then the viral DNA becomes part of the host’s DNA as a provirus.

Section 18.1 Summary – pages Retrovirus Cycle Exiting cell Reverse transcriptase Retrovirus Entering cell RNA DNA DNA is made from the viral RNA. mRNA New virus parts New virus forming Provirus in host chromosome Retrovirus Cycle

Section 1 Check Question 1 Which of the following is NOT a reason that viruses are considered to be nonliving? D. Viruses don’t develop. C. Viruses don’t grow. B. Viruses don’t respire. A. Viruses don’t replicate. The answer is A.

Section 1 Check Question 2 Which is NOT a component of a virus? D. phage C. DNA B. capsid A. RNA The answer is D.

Section 1 Check Question 3 Which of the following is NOT determined by the arrangement of proteins in the capsid of a virus? D. how the virus infects a cell C. whether or not the virus will have an envelope around it B. what cell can be infected by the virus A. shape The answer is C.

Section 1 Check Question 4 What two ways do viruses have of getting into host cells? Answer The virus can inject its nucleic acid into the host cell, or attach to the host cell ’ s membrane and become surrounded by the membrane and placed in a vacuole. The virus then bursts out of the vacuole and releases its nucleic acid into the cell.

Question 5 In the lytic cycle, after the host ’ s metabolic machinery makes viral nucleic acid and proteins the next phase is _______. D. attachment C. assembly B. replication A. lysis and release The answer is C. In the assembly phase, the new virus particles are assembled.

Ch 18.2 Bacteria Bacteria Bacteria Importance Bacteria Diseases Bacterial Reproduction

Section 2 Check Which of the following is not a way to identify bacteria? Question 6 D. lack of a plasma membrane C. characteristic growth patterns B. shape A. the way in which their cell walls reflect Gram stain The answer is D.

Given their rapid reproductive rates, why aren ’ t there more bacteria than there actually are? Question 7 Answer Bacteria don’t always have ideal growing conditions. They run out of nutrients and water, they poison themselves with their own wastes, and predators eat them.

Section 2 Check What is a pilus used for in a bacterium? Question 8

Section 2 Check A pilus helps a bacterium stick to a surface. It is also a bridge through or on which two bacteria can exchange DNA. Capsule Cell Wall Chromosome Flagellum Plasmid Pilus Plasma membrane

Chapter Assessment Question 9 With lysogenic viruses, what two phases of the lytic cycle are replaced by the lysogenic cycle? D. attachment and entry C. assembly and lysis and release B. replication and assemble A. entry and replication

The answer is D. LYSOGENIC CYCLE LYTIC CYCLE A. Attachment and Entry Chapter Assessment

Question 10 Explain why you can be infected with a virus but may have no symptoms of disease for years after the initial infection. Answer The virus enters a lysogenic phase remaining inactive but replicating along with the host cell’s chromosomes. Eventually, the virus enters a lytic phase where it destroys its host cells and causes symptoms of disease.

Chapter Assessment Question 11 What is the difference between lysis and exocytosis with respect to host cells that contain viruses? Answer Lysis, the bursting of the host cell, is caused when viruses break out of it. In exocytosis, the virus is enclosed in a vacuole that then fuses with the host cell’s plasma membrane. The virus is then released to the outside.

Chapter Assessment Question 12 What is the importance of reverse transcriptase to a retrovirus? Answer The enzyme reverse transcriptase allows the retrovirus to make DNA from its RNA so the DNA may attach to the chromosomes of the host cell and divide with the host cell.

Chapter Assessment Question 13 Particles that are composed of proteins but have no nucleic acid to carry genetic information are _______. D. retroviruses C. viroids B. prions A. proviruses The answer is B.

Chapter Assessment During ______, a bacterium transfers all or part of its chromosome to another bacterium. D. chemosynthesis C. conjugation B. attachment A. binary fission The answer is C. Question 14

Chapter Assessment What causes botulism? Answer Endospores of C. botulinum bacteria get into an anaerobic environment like improperly canned food, germinate, and produce a toxin as they grow. This toxin is then ingested by humans and causes poisoning called botulism. Question 15

Chapter Assessment What causes anthrax? Question 16

Endospores of B. anthracis bacteria produce endospores that can become airborne, and if inhaled in large amounts, can germinate in a person’s lungs causing a deadly infection that damages lung tissue and the circulatory system. Chapter Assessment

Question 17 Describe the process in which bacteria make nitrogen in the air accessible for use by plants.

Several species of bacteria have enzymes that convert nitrogen gas into ammonia. Other bacteria then convert the ammonia into nitrite and nitrate that plants can use. Answer Chapter Assessment

Question 18 What are the two ways in which bacterial diseases harm people? Answer The growth of the bacteria can interfere with the normal function of body tissue, or the bacteria can release a toxin that directly attacks the host.