Chapter 18: Viruses and Prokaryotes



Chapter 18: Viruses and Prokaryotes

Resources

Student Edition Labs

Examining Bacteria in Yogurt p. 560

Leaf Print Bacteria p. 562

Options for Inquiry

Using Bacteria to Break Down Oil p. 566

Modeling Viruses p. 567

Lab Binder

Additional Investigation: Viruses and Cancer p. 23-25

Biotechnology Lab: Bacteria’s Role in Wastewater Treatment p. 39-42

Virtual Lab Worksheet: Testing Antibacterial Agents p. 54

Power Presentations

Presentation Chapter 18

Media Gallery

Bacteriophage

Antibiotics and Illness

Streptococcus bacteria

Ebola Virus Testing

Power Notes

Video

Examine bacteria and antibiotic resistance.

Animated Biology

Viral Infections

What Would You Prescribe?

Transparencies

Viral Structure T77

Lytic and Lysogenic Infections T78

Prokaryotic Structures T79



18.1: Studying Viruses and Prokaryotes

Objectives: Compare and contrast different types of infectious agents.

Warm Up: Why is it that when you go to a doctor, explain your symptoms, and undergo testing, sometimes you are given an antibiotic and sometimes you are not?

Words to Know: Virus, Pathogen, Viroid, Prion, prokaryote, archaea

Viruses, Bacteria, Viroids, and Prions

• A Virus is an infectious particle made only of a strand of DNA or RNA surrounded by a protein coat.

• A virus is NON LIVING

• Bacteria are one-celled microorganisms that can also cause infection.

• A Pathogen is any organism or particle that can cause an infectious disease.

• Viroids are infectious particles that cause disease in plants.

• Made of single-stranded RNA without a protein coat.

• They are passed through seeds or pollen.

• A Prion is an infectious particle made only of proteins that can cause other proteins to fold incorrectly.

• When proteins misfold they do not work correctly.

• Ex: mad cow disease.

Why are viruses, viroids, and prions not included in the Linnaean system of biological classification?

18.1 Assessment p. 545 (1-5)

Trends in Infectious Disease p. 546

18.2: Viral Structure and Reproduction

Objectives: Identify the structures and shapes of viruses.

Describe different types of viral infection.

Warm Up: At what point does the virus become dangerous. How do viruses enter the human population?

Words to Know: Capsid, Bacteriophage, Lytic Infection, Lysogenic Infection, Prophage, Endocytosis, lipid

Viruses

• Virus comes from the Latin word for “poison”.

The Structure of Viruses

• A single viral particle (virion) is made up of genetic material surrounded by a protein shell called a Capsid.

• Capsids have different shapes due to the proteins that make them up.

• Some viruses attach to host cells by spikes.

• Viruses can only reproduce after they have infected host cells.

• The structure and shape of viruses play an important role in how they work.

• Each type of virus can infect only certain hosts.

• A virus identifies its host cell, by fitting its surface proteins to receptor molecules on the surface of the host cell, like a key fitting a lock.

• Viruses can have DNA or RNA, but NEVER both.

Viruses that Infect Bacteria

• Bacteriophages are viruses that prey on bacteria.

• A bacteriophage will attach to the host cell.

• The bacteriophage’s tail releases an enzyme that breaks down part of the bacterial cell wall.

• The tail core punches through the cell wall, injecting the phage’s DNA.

Describe how the structures of a bacteriophage are well-suited for their functions.

Viruses Cause Two Types of Infections

• Once inside the host cell, phages follow one of two general paths in causing disease.

• Neither path is good for the host.

Lytic Infection

• A Lytic infection pathway in which the host cell bursts, releasing the new viral offspring into the host’s system, where each then infects another cell.

• 1. Virus ATTACHES to the host cell.

• 2. Virus INJECTS its DNA into the host cell.

• 3. The viral DNA forms a circle.

• 4. The viral DNA directs the host cell to produce new viral parts that assemble into new viruses.

• 5. The host cell breaks apart (lyses), releases new viruses to infect other cells.

Lysogenic Infection

• A Lysogenic Infection is an infection pathway in which the host cell bursts releasing the new viral offspring into the host’s system, where each then infects another cell.

• 1. Virus ATTACHES to the host cell.

• 2. Virus INJECTS its DNA into the host cell.

• 3. The viral DNA forms a circle.

• 4. The viral DNA is called a prophage when it combines with the hot cell’s DNA.

• 5. Although the prophage is not active, it replicates along with the host cell’s DNA.

• 6. Many cell divisions produce a bunch of cells infected with prophage.

• 7. The prophage leaves the host’s DNA and enters the lytic cycle.

• 8. The viral DNA directs the host cell to produce new viral parts that assemble into new viruses.

• 9. The host cell break apart (lyses), releases new viruses to infect other cells.

Using the analogy of viral infections resembling houseguests, explain which describes a lytic and which describes a lysogenic infection.

18.2 Assessment p. 551 (1-5)

18.3: Viral Diseases

Objectives: Identify the names and symptoms of several viral diseases.

Describe how vaccines are made.

Warm Up: What vaccinations are commonly given to young children?

Words to Know: Epidemic, Vaccine, Retrovirus

Viruses and Disease

• Viruses go through several defense systems before they reach their targets and cause illness.

First Defenses

• In vertebrates, a virus must pass through the skin, but in other organisms it may be outer skeletons or cell walls.

• They can also enter through an opening (cuts, mucous membranes, nose, genital area, eyes and ears).

• Once inside the body, the virus finds its way to its target organ or tissue.

Examples of Viral Infections

Influenza

• The flu spreads quickly and can result in frequent local epidemics.

• An Epidemic is a rapid outbreak of an infection that affects many people.

• There is a vaccine – a substance that stimulates the body’s own immune response against invasion by microbes – for the flu to help contain outbreaks.

SARS

• Severe Acute Respiratory Syndrome (SARS) is another viral respiratory disease.

• It has symptoms similar to the flue such as coughing, difficulty and difficulty breathing.

• There are current clinical trials for a SARS vaccine.

HIV

• Human Immunodeficiency Virus (HIV) is a retrovirus.

• A Retrovirus is a virus that contains RNA and uses an enzyme called Reverse Transcriptase to make a DNA Copy.

• Double stranded DNA then enters the nucleus and combines with the host’s genes as a lysogenic infection.

• The viral DNA can they remain dormant for years as a provirus causing NO symptoms.

• When the virus becomes active, it directs the formation of new viral parts and infects more cells.

• HIV attacks human white blood cells and the loss of these cells eventually causes AIDS (Acquired Immune Deficiency Syndrome).

How do retroviruses work differently from regular viruses?

Vaccines are made from Weakened Pathogens

• In the U.S. children are vaccinated at an early age against disease such as measles, mumps, rubella (MMR) and chickenpox.

• A vaccine is made from the same pathogen – disease causing agent – that it is supposed to protect against.

• Vaccines consist of weakened versions of the virus, or parts of the virus, that will cause the body to produce a response.

• The body then builds up immunity to the virus so that when it comes in contact with the actual virus it is able to protect itself.

• Vaccines cause a mild immune response.

Before the chickenpox vaccination was available, children were often purposely exposed to the virus at a young age. What was the reason for doing this?

18.3 Assessment p. 554 (1-5)

18.4: Bacteria and Archaea

Objectives: Describe different types of prokaryotes.

Summarize the similarities and differences between bacteria and archaea.

Describe the survival strategies of bacteria.

Warm Up: What kinds of products and innovations can we use that kill bacteria or keep them away from us?

Words to Know: Obligate Anaerobe, Obligate Aerobe, Facultative Aerobe, Plasmid, Flagellum, Conjugation, Endospore.

Prokaryotes on Earth

• Prokaryotes are the most widespread and abundant organisms on Earth.

• Scientists estimate that there are more than 1 billion types of bacteria and more than 1030 individual prokaryotic cells on, above and under Earth’s surface.

• Prokaryotes can be grouped base don their need for oxygen.

• Prokaryotes that cannot live in the presence of oxygen are called Obligate Anaerobes.

• They are actually Poisoned by Oxygen.

• Archaea are prokaryotes that live in extreme environments and are obligate anaerobes.

• In contrast, some prokaryotes need the presence of oxygen in their environment.

• Organisms that need oxygen are called Obligate Aerobes.

• There are also prokaryotes that can survive whether oxygen is present in the environment or not.

• This type of prokaryote is called a Facultative Aerobe.

Bacteria and Archaea

• Domain Bacteria and Domain Archaea comprise all of Earth’s prokaryotes.

• Domain Bacteria is the more diverse and widespread of the two domains while Domain Archaea are found in the more extreme conditions.

Structural Comparisons

• Both Bacteria and Archaea have similar structures.

• Bacteria are often named based upon their shapes:

• Rod-shaped are Bacilli

• Spiral-shaped are Spirilla

• Spherical-shaped are Cocci

• Bacteria are also named for how they grow:

• Those that grow in Pairs are Diplo

• Those that grow in Chains are Strepto

• Those that grow in Clusters are Staphlo

• Prokaryotes do NOT have any membrane-bound organelles, such as a nucleus containing double-stranded DNA.

• Instead their DNA is in a circle surrounded by the cytoplasm.

• A Plasmid is a small piece of genetic material that can replicate separately from the prokaryote’s main chromosome.

• Many bacteria and archaea move by gliding or using flagella – a long whip-like structure used for movement.

• Many prokaryotes also contain structures called pili that are thinner, shorter and often more numerous than flagella.

• They help the prokaryote to stick to surfaces and to other prokaryotes.

Molecular Comparisons

• Molecular comparisons show where the differences are in archaea and bacteria.

• Archaea cell walls and membranes are chemically different from those of bacteria.

• The membranes of archaea contain lipids that are NOT found in any other type of organism on earth and bacteria have peptidoglycan in their cell walls which archaea do not.

• The amount of peptidoglycan in their cell walls is an important characteristic of bacteria.

• A staining method called a Gram stain is used to tell the two groups apart.

• The Gram stain is important for diagnosing infectious bacterial diseases and it sometimes help determine the type of medicine a doctor chooses to fight infection.

• Archaea are typically Gram Negative.

• Bacteria that can be treated with antibiotics like Penicillin.

Archaea were first named archaeabacteria, a term that you may still find in some books and articles. What are two differences between archaea and bacteria.

Bacteria Survival

Gene Exchange in Prokaryotes

• Prokaryotes divide by Binary Fission.

• DNA (plasmid) is copied.

• Cell divides into two new identical cells.

• In Conjugation, genetic material transfers between prokaryotes, producing genetic variation.

• A conjugation bridge forms from the donor cell to a recipient cell.

Surviving Harsh Conditions

• Some bacteria can produce an Endospore, a specialized cell with a thick, protective wall.

• The Endospore can then survive harsh climates until a better situation comes along.

Why are disinfectants alone not enough to kill ALL types of bacteria?

18.4 Assessment p. 558 (1-6)

18.5: Beneficial Roles of Prokaryotes

Objectives: Describe way prokaryotes provide nutrients to humans and other animals.

Recognize the roles prokaryotes play in ecosystems.

Warm Up: What kinds of foods require bacteria for their production? What role do bacteria play in agriculture?

Words to Know: Bioremediation, nitrogen fixation.

Prokaryotes Provide Nutrients to Humans and Other Animals

• Prokaryotes are a key part of animal digestive systems.

• Prokaryotes have a mutualistic relationship with the host animal and break down food while getting a place to live.

• Without this bacteria, harmful bacteria would come in and replace that niche.

• Many food we enjoy are fermented by bacteria.

• Yogurt, cheese, pickles, soy sauce, sauerkraut, and vinegar.

What are two ways in which prokaryotes that live within our bodies are helpful to us?

Quick Lab: Examining Bacteria in Yogurt p. 560

Prokaryotes Play Important Roles in Ecosystems

• Cyanobacteria produce oxygen through photosynthesis.

• Remember fossil evidence suggest that there was VERY LITTLE oxygen before cyanobacteria.

• Others help recycle carbon, nitrogen, hydrogen and sulfur through the ecosystem.

• Some colonies of photosynthesizing cyanobacteria, as well as other bacteria, are able to fix nitrogen.

• Nitrogen Fixation is the process of converting atmospheric nitrogen into ammonia and other nitrogen compounds that plants can use.

• One important use of bacteria is in Bioremediation, a process that uses microbes and other living things to break down pollutants.

• Ex: Some bacteria can break down oil from oil spills.

• Ex: Most bacteria can break down poisons and are therefore useful in recycling and composting.

When there is a toxic chemical spill, sometimes workers will spray bacteria over the contaminated area. Why might they do this?

18.5 Assessment p. 561 (1-5)

Investigation: Leaf Print Bacteria p. 562

18.6: Bacterial Diseases and Antibiotics

Objectives: Explain how bacteria cause diseases.

Describe how antibiotics work and the potential for antibiotic resistance.

Warm Up: If we regard ourselves as being under attack by a viruses and bacteria, how do we fight back? Who can adapt faster ot the tactics of the other – humans or bacteria?

Words to Know: Toxin, Antibiotic, homeostasis

Some Bacteria Cause Disease

• Some bacteria cause disease in plants and animals by disrupting the host organism’s homeostasis, internal stable environment.

• There are two ways bacteria can cause illness:

• 1. Invading Tissues

• Ex: Tuberculosis (TB) invades the tissues in the lungs and destroys white blood cells.

• 2. Creating Toxins (poisons) that can be carried by the blood through the body.

• Ex: Staphylococcus aureus can cause food poisoning.

Antibiotics are Used to Fight Bacterial Disease.

• Why do you get antibiotics for strep. throat but not a cold?

• Viruses cause colds and cannot be destroyed antibiotics.

• Antibiotics are chemicals that kill or slow the growth of bacteria.

• They work by preventing the bacterial cells from making their cell walls.

• Antibiotics are produced naturally by some species of bacteria and fungus.

• Antibiotics should NOT be the first line of defense, prevention should.

• Antibiotics can not only destroy the bad bacteria, but the good bacteria as well.

Bacteria can Evolve Resistance to Antibiotics

• The inappropriate and incomplete use of antibiotics has produced a serious public health issue – multi-drug resistant bacteria.

• Resistance occurs as a result of natural selection, as individuals who are more resistant survive and reproduce.

• There are three causes for drug resistant bacteria:

• 1. Overuse – the use of antibiotics when not necessary lead to stronger strains.

• 2. Underuse – failure to take the entire course of antibiotics when ill allows surviving bacteria to reproduce.

• 3. Misuse – when dealing with animals, healthy animals can be exposed to antibiotics used for growth.

How can you use “superbugs” as an example of natural selection?

18.6 Assessment p. 565 (1-6)

Options for Inquiry: Using Bacteria to Break Down Oil p. 566

Investigation: Modeling Viruses p. 567



Chapter Assessment p. 569-571

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