Ch 18 Viruses and Bacteria

04 Biology 2008

From Mrs. C. Phillips, DHS

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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

• The arrangement of proteins in the capsid of a virus determines the virus’s shape.

Nucleic acidCapsid

• 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 and2. Lysogenic Cycle

Each cycle first involves attachment to the host cell.

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. ReplicationD. 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 calleda provirus when it becomespart of the host’s

chromosome.

C. Cell Division

Althoughthe provirusis inactive,it replicatesalong withthe host cell’schromosome.

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.

Retrovirus Cycle

Exiting cell

Reverse transcriptase

Retrovirus

Enteringcell

RNA

RNA

DNA

DNA is made from the viral RNA.

mRNA

New virus parts

New virus forming

Provirus in host chromosome

Retrovirus Cycle

Question 1Which 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.

Question 2

Which is NOT a component of a virus?

D. phage

C. DNA

B. capsid

A. RNA

The answer is D.

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.

Question 4What two ways do viruses have of getting into host cells?

AnswerThe 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 5In 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

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.

What is a pilus used for in a bacterium?

Question 8

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

PlasmidPilus

Plasma membrane

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

Question 10Explain why you can be infected with a virus but may have no symptoms of disease for years after the initial infection.

AnswerThe 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.

Question 11What is the difference between lysis and exocytosis with respect to host cells that contain viruses?

AnswerLysis, 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.

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.

Question 13Particles that are composed of proteins but have no nucleic acid to carry genetic information are _______.

D. retroviruses C. viroids

B. prionsA. proviruses

The answer is B.

During ______, a bacterium transfers all or part of its chromosome to another bacterium.

D. chemosynthesisC. conjugation

B. attachment A. binary fission

The answer is C.

Question 14

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

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.

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

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.