Monday, March 8thMonday, March 8th Check Chapter #20 PretestCheck Chapter #20 Pretest Discuss Section 20-1 NotesDiscuss Section 20-1 Notes 20-1 Review Sheet due next time20-1 Review Sheet due next time Quiz next time: 20-1 NotesQuiz next time: 20-1 Notes Chapter #20 Vocabulary Quiz Friday, Chapter #20 Vocabulary Quiz Friday,

March 12thMarch 12th

Chapter #20Chapter #20Viruses &Viruses &BacteriaBacteria

Section 20-1Section 20-1VirusesViruses

A. History of VirusesA. History of Viruses1) The first viruses discovered were ones 1) The first viruses discovered were ones

that infected that infected tobaccotobacco plants, a disease plants, a disease called called TMVTMV ( (tobacco mosaic virustobacco mosaic virus))

2) One experiment that attempted to 2) One experiment that attempted to identify the virus involved the use of a identify the virus involved the use of a fine porcelain filter:fine porcelain filter:a) a) The pores in these filters were so The pores in these filters were so

small that bacteria could not pass small that bacteria could not pass through.through.

b) b) However, the infectious agent of However, the infectious agent of TMV passed through the filters TMV passed through the filters without difficulty.without difficulty.

c) Scientists concluded that the infectious c) Scientists concluded that the infectious agent must be agent must be smallersmaller than a than a bacterialbacterial cell.cell.

d) They discovered the agent could only d) They discovered the agent could only reproduce inside reproduce inside livingliving cells. cells.

e) They called the agent a e) They called the agent a virusvirus, a Latin , a Latin word for “word for “poisonpoison”.”.

3) For many years after their discovery, 3) For many years after their discovery, viruses were erroneously regarded as viruses were erroneously regarded as primitive forms of life. Scientists thought primitive forms of life. Scientists thought viruses were tiny viruses were tiny cellscells that might have been that might have been the ancestors of the ancestors of bacteriabacteria..

4) The true nature of viruses was discovered 4) The true nature of viruses was discovered in 1933 by biologist Wendell Stanleyin 1933 by biologist Wendell Stanley

a) a) When Stanley tried to purify an extract When Stanley tried to purify an extract of TMV, the extract formed crystals…a of TMV, the extract formed crystals…a property of chemicals.property of chemicals.

b) b) The crystals retained the ability to infect The crystals retained the ability to infect healthy tobacco plants & were therefore healthy tobacco plants & were therefore the virus itself.the virus itself.

c) Stanley concluded that TMV is c) Stanley concluded that TMV is chemical chemical mattermatter rather than a living organism. rather than a living organism.

5) Within a few years of Stanley’s findings, 5) Within a few years of Stanley’s findings, scientists were able to disassemble TMV scientists were able to disassemble TMV & confirm Stanley’s conclusion that & confirm Stanley’s conclusion that viruses were in fact chemicals and not viruses were in fact chemicals and not living cells.living cells.In fact, each particle of TMV is made of In fact, each particle of TMV is made of only two kinds of molecules:only two kinds of molecules:a) a) RNARNAb) b) ProteinProtein

6) Later, scientists were able to separate the 6) Later, scientists were able to separate the RNA from the protein. When they RNA from the protein. When they reassembled the two components, the reassembled the two components, the reconstructed TMV particles were fully reconstructed TMV particles were fully able to infect healthy tobacco plants.able to infect healthy tobacco plants.

7) Biologists have concluded that viruses 7) Biologists have concluded that viruses are NOT living organisms.are NOT living organisms.Instead, a virus is Instead, a virus is a strand of nucleic acid a strand of nucleic acid encased in a protein coat that an infect encased in a protein coat that an infect cells and replicate within them.cells and replicate within them.

B. Structure of VirusesB. Structure of Viruses1) Most viruses have a protein sheath 1) Most viruses have a protein sheath

called a called a capsidcapsid surrounding a core of surrounding a core of nucleic acidnucleic acid..a) a) Many plant viruses as well as some Many plant viruses as well as some

animal viruses contain RNA.animal viruses contain RNA.b) b) The nucleic acid found in most viruses The nucleic acid found in most viruses

is DNA.is DNA.

2) Many viruses found in animals, such as the 2) Many viruses found in animals, such as the influenza virus, have a membranous influenza virus, have a membranous envelopeenvelope surrounding the capsid. surrounding the capsid.

a) a) The envelope helps it gain entry into The envelope helps it gain entry into cells.cells.

b) b) It contains proteins, lipids, & It contains proteins, lipids, & glycoproteins derived from the host cell.glycoproteins derived from the host cell.

3) Viruses differ greatly in appearance3) Viruses differ greatly in appearancea) The simplest viruses consist of a single a) The simplest viruses consist of a single

molecule of a nucleic acid & a capsid molecule of a nucleic acid & a capsid made of a single protein or a few made of a single protein or a few different protein molecules repeated different protein molecules repeated several times.several times.

b) More complex viruses may consist of b) More complex viruses may consist of several different segments of DNA or several different segments of DNA or RNA contained within a capsid made of RNA contained within a capsid made of several different kinds of protein.several different kinds of protein.

c) c) TMV is rodlike in appearance, with TMV is rodlike in appearance, with capsid proteins winding around the core capsid proteins winding around the core like a helix.like a helix.

d) The capsid of most polyhedral viruses is d) The capsid of most polyhedral viruses is in the shape of an in the shape of an icosahedronicosahedron, which is a , which is a shape with shape with 2020 triangular faces and triangular faces and 1212 corners.corners.

The The adenovirusadenovirus, which causes upper , which causes upper respiratory infections in humans, has the respiratory infections in humans, has the icosahedral shape.icosahedral shape.

e) e) BacteriophagesBacteriophages are viruses that infect are viruses that infect bacteria. They have a very complicated bacteria. They have a very complicated structure shown in Figure 20-5 on p. 457structure shown in Figure 20-5 on p. 457

C. Viruses Reproduce Inside Living Cells C. Viruses Reproduce Inside Living Cells 1) 1) Viruses lack the enzymes for Viruses lack the enzymes for

metabolism & have no ribosomes or metabolism & have no ribosomes or other equipment for protein synthesis. other equipment for protein synthesis. Therefore they must rely on living cells Therefore they must rely on living cells for reproduction.for reproduction.

2) Before a virus can reproduce, it must 2) Before a virus can reproduce, it must first infect a living cell.first infect a living cell.a) Bacteriophages punch a hole in the a) Bacteriophages punch a hole in the

bacterial cell wall & inject their bacterial cell wall & inject their DNADNA into the cell like a hypodermic needle.into the cell like a hypodermic needle.

b) Plant viruses, like TMV, enter plant b) Plant viruses, like TMV, enter plant cells through cells through tiny ripstiny rips in the in the cell wallcell wall at at points of points of injuryinjury..

c) Animal viruses enter the host cell by c) Animal viruses enter the host cell by endocytosisendocytosis..

3) Once they are inside a cell, many viruses 3) Once they are inside a cell, many viruses are are pathogenspathogens….agents that cause disease.….agents that cause disease.

4) Before any virus can be engulfed by a cell, 4) Before any virus can be engulfed by a cell, it must first bind to the cell membrane.it must first bind to the cell membrane.a) The envelope of an animal virus has a) The envelope of an animal virus has

spikes of spikes of glycoproteinsglycoproteins & lipids that are & lipids that are able to bind to specific able to bind to specific receptor receptor moleculesmolecules on the cell membrane. on the cell membrane.

b) An animal virus is able to infect only b) An animal virus is able to infect only cells with surface receptor proteins to cells with surface receptor proteins to which the virus’ envelope molecules can which the virus’ envelope molecules can attach.attach.

c) This is why viruses affect very specific c) This is why viruses affect very specific cells in their host, the spikes of the virus cells in their host, the spikes of the virus will only attach to will only attach to specific receptor specific receptor proteinsproteins..

5) Mammals protect themselves from viral 5) Mammals protect themselves from viral infection by producing infection by producing antibodiesantibodies to the to the virus envelope’s glycoprotein.virus envelope’s glycoprotein.a) a) An antibody is a protein secreted by An antibody is a protein secreted by

cells in the immune system in response to cells in the immune system in response to a foreign substance in the body.a foreign substance in the body.

b) However, b) However, mutationsmutations in viruses often in viruses often change their glycoproteins & make it change their glycoproteins & make it difficult for the antibodies to difficult for the antibodies to recognizerecognize the virus.the virus.

c) Mutations in the virus genes that encode c) Mutations in the virus genes that encode the structure of its glycoproteins may the structure of its glycoproteins may also enable the virus to bind to a receptor also enable the virus to bind to a receptor protein it failed to recognize earlier.protein it failed to recognize earlier.

D. How HIV Infects Human WBC’sD. How HIV Infects Human WBC’s1) HIV gains access to a WBC by first 1) HIV gains access to a WBC by first

binding to the binding to the cell membranecell membrane..2) The binding triggers 2) The binding triggers endocytosisendocytosis..3) The virus enters the cell within a 3) The virus enters the cell within a

membrane-bound membrane-bound vesiclevesicle, which soon , which soon releases the virus into the cell releases the virus into the cell cytoplasmcytoplasm..

4) Once within the host, HIV sheds its 4) Once within the host, HIV sheds its envelopeenvelope & & capsidcapsid, leaving two strands of , leaving two strands of the virus’ the virus’ RNARNA floating in the cytoplasm. floating in the cytoplasm.

5) HIV utilizes the enzyme 5) HIV utilizes the enzyme reverse reverse transcriptasetranscriptase, which manufactures , which manufactures DNADNA from its from its RNARNA. This ability makes HIV a . This ability makes HIV a retrovirusretrovirus..

6) After the viral RNA is transcribed into 6) After the viral RNA is transcribed into DNA, the DNA, the genesgenes are translated into HIV are translated into HIV proteinsproteins..

7) The host cell’s machinery is then used to 7) The host cell’s machinery is then used to produce & assemble many copies of the produce & assemble many copies of the HIV virus.HIV virus.

8) Some of the newly assembled virus 8) Some of the newly assembled virus particles leave the cell by particles leave the cell by exocytosisexocytosis, and , and eventually the host cell eventually the host cell rupturesruptures, releasing , releasing thousands of additional virus particles.thousands of additional virus particles.

9) These newly released virus particles are 9) These newly released virus particles are then free to infect other WBC’s and then free to infect other WBC’s and continue the cycle of infection.continue the cycle of infection.

E. Origins of VirusesE. Origins of Viruses

1) 1) Viruses are considered to be escaped Viruses are considered to be escaped fragments of host genomes.fragments of host genomes.

2) This is why viruses are almost always 2) This is why viruses are almost always highly specific to the host they infect.highly specific to the host they infect.

Tuesday, March 16thTuesday, March 16th

Check Directed & Active ReadingCheck Directed & Active Reading

Discuss Sections 20-2 & 20-3 NotesDiscuss Sections 20-2 & 20-3 Notes

Review Sheet due ThursdayReview Sheet due Thursday

Quiz Thursday: 20-2 & 20-3 NotesQuiz Thursday: 20-2 & 20-3 Notes

Section 20-2Section 20-2BacteriaBacteria

A. Bacteria are small, single cells and are the A. Bacteria are small, single cells and are the only ones characterized by only ones characterized by prokaryoticprokaryotic organization.organization.

B. A bacterial cell is usually one of three B. A bacterial cell is usually one of three basic shapes:basic shapes:

1) 1) Bacillus: Rod-shaped cellsBacillus: Rod-shaped cells

2) 2) Coccus: Spherical cellsCoccus: Spherical cells

3) 3) Spirillum: Spiral cellsSpirillum: Spiral cells

C. Bacteria differ in cell wall structure.C. Bacteria differ in cell wall structure.

1) A bacterium’s plasma membrane is 1) A bacterium’s plasma membrane is encased within a encased within a cell wallcell wall..

2) Some 2) Some eubacteriaeubacteria have a cell wall have a cell wall covered with an outer membrane layer covered with an outer membrane layer made of large molecules called made of large molecules called lipopolysaccharideslipopolysaccharides..

3) Outside of the cell wall & membrane, 3) Outside of the cell wall & membrane, many bacteria have a gelatinous layer many bacteria have a gelatinous layer called a called a capsulecapsule..

D. Bacteria are commonly classified by D. Bacteria are commonly classified by differences in their cell walls.differences in their cell walls.

1)1) Gram Positive bacteria have a cell wall Gram Positive bacteria have a cell wall containing a large amount of containing a large amount of peptidoglycan.peptidoglycan.

2)2) Gram Negative bacteria have a cell wall Gram Negative bacteria have a cell wall containing a thin layer of peptidoglycan containing a thin layer of peptidoglycan covered by an outer membrane.covered by an outer membrane.

E. Danish microbiologist E. Danish microbiologist Hans GramHans Gram developed a staining procedure in 1884 that developed a staining procedure in 1884 that allows scientists to distinguish between allows scientists to distinguish between Gram+ and Gram- bacteria.Gram+ and Gram- bacteria.

F. F. The staining method is based on the fact The staining method is based on the fact that the thick cell wall of Gram+ bacteria that the thick cell wall of Gram+ bacteria will hold on to a stain, while the stain will will hold on to a stain, while the stain will be washed out of the thin cell wall of Gram- be washed out of the thin cell wall of Gram- bacteria.bacteria.

G. Steps in the Gram StainG. Steps in the Gram Stain1) Cover the smear with crystal violet stain 1) Cover the smear with crystal violet stain

and let it react for 60 seconds.and let it react for 60 seconds.2) Pour off the excess stain and gently rinse 2) Pour off the excess stain and gently rinse

with water.with water.3) Cover the smear with Gram’s iodine 3) Cover the smear with Gram’s iodine

and let it react for 60 seconds.and let it react for 60 seconds.4) Gently rinse the smear with ethanol 4) Gently rinse the smear with ethanol

until no stain rinses off.until no stain rinses off.

5) Rinse off the alcohol with water.5) Rinse off the alcohol with water.6) Cover the smear with Safranin & let it 6) Cover the smear with Safranin & let it

react for 15 seconds.react for 15 seconds.7) Rinse the slide with water.7) Rinse the slide with water.8) Gently blot the slide dry.8) Gently blot the slide dry.

H. Medical Importance of Gram StainingH. Medical Importance of Gram Staining1) 1) Gram+Gram+ bacteria tend to be killed by bacteria tend to be killed by

penicillin.penicillin.2) 2) Gram-Gram- bacteria tend to be resistant to bacteria tend to be resistant to

penicillin, but are much more susceptible penicillin, but are much more susceptible to tetracycline.to tetracycline.

3) This is why doctors try to identify the 3) This is why doctors try to identify the type of bacteria causing a disease before type of bacteria causing a disease before prescribing a certain antibiotic.prescribing a certain antibiotic.

I. Some bacteria form thick-walled I. Some bacteria form thick-walled endosporesendospores around their chromosomes and around their chromosomes and a small bit of cytoplasm when they are a small bit of cytoplasm when they are exposed to harsh conditions.exposed to harsh conditions.

1) These endospores are highly resistant to 1) These endospores are highly resistant to environmental stress & may germinate environmental stress & may germinate after years to form new, active bacteria.after years to form new, active bacteria.

2) Endospores of 2) Endospores of Clostridium botulinumClostridium botulinum are responsible for are responsible for botulismbotulism, a very , a very serious form of food poisoning.serious form of food poisoning.

J. Bacteria vs. EukaryotesJ. Bacteria vs. Eukaryotes

1) Bacteria are prokaryotic. They lack a 1) Bacteria are prokaryotic. They lack a nucleus & membrane-bound organelles.nucleus & membrane-bound organelles.

2) Eukaryotic cells are about 10x larger 2) Eukaryotic cells are about 10x larger than bacterial cells.than bacterial cells.

3) All bacteria are single-celled. 3) All bacteria are single-celled. Eukaryotes can be unicellular or Eukaryotes can be unicellular or multicellular.multicellular.

4) Bacterial chromosomes consist of a 4) Bacterial chromosomes consist of a single circular strand of DNA. single circular strand of DNA. Eukaryotes have more complex DNA.Eukaryotes have more complex DNA.

5) Bacteria divide by binary fission. Most 5) Bacteria divide by binary fission. Most eukaryotes divide by mitosis & meiosis.eukaryotes divide by mitosis & meiosis.

6) Eukaryotic flagella are more complex 6) Eukaryotic flagella are more complex than bacterial flagella. Some bacteria than bacterial flagella. Some bacteria have shorter, thicker outgrowths called have shorter, thicker outgrowths called pili.pili.

7) Bacteria have many different types of 7) Bacteria have many different types of metabolism. All eukaryotes have the metabolism. All eukaryotes have the same general metabolic requirements.same general metabolic requirements.

K. Bacterial MetabolismK. Bacterial Metabolism1) 1) PhotosyntheticPhotosynthetic bacteria utilize sunlight bacteria utilize sunlight

for their energy source. Examples for their energy source. Examples include cyanobacteria, green sulfur include cyanobacteria, green sulfur bacteria, purple sulfur bacteria, and bacteria, purple sulfur bacteria, and purple nonsulfur bacteriapurple nonsulfur bacteria

2) 2) ChemoautotrophicChemoautotrophic bacteria utilize bacteria utilize electrons in inorganic molecules. electrons in inorganic molecules. Examples include Examples include NitrosomonasNitrosomonas and and NitrobacterNitrobacter..

3) 3) HeterotrophicHeterotrophic bacteria utilize organic bacteria utilize organic material from other organisms. Most material from other organisms. Most bacteria are heterotrophic.bacteria are heterotrophic.

Section 20-3:Section 20-3:Bacteria & VirusesBacteria & Viruses

as Pathogensas Pathogens

Diseases caused by Bacteria: Table 20-1Diseases caused by Bacteria: Table 20-1

Diseases caused by Viruses: Table 20-2Diseases caused by Viruses: Table 20-2

B. Treating Bacterial DiseasesB. Treating Bacterial Diseases1) In 1928, the British bacteriologist 1) In 1928, the British bacteriologist

Alexander FlemingAlexander Fleming observed a observed a PennicilliumPennicillium mold growing on a bacterial culturemold growing on a bacterial culture

2) He noticed the 2) He noticed the bacteriabacteria did not grow near did not grow near the the moldmold..

3) He isolated the substance that killed the 3) He isolated the substance that killed the bacteria and named it bacteria and named it penicillinpenicillin..

4) Penicillin is an 4) Penicillin is an antibioticantibiotic, which is a drug , which is a drug used to fight pathogenic microorganisms.used to fight pathogenic microorganisms.a) a) Antibiotics work by interfering with the Antibiotics work by interfering with the

microorganism’s cellular processes.microorganism’s cellular processes.b) b) Antibiotics can’t be used to fight viral Antibiotics can’t be used to fight viral

diseases.diseases.5) Scientists are concerned because many 5) Scientists are concerned because many

microorganisms are becoming microorganisms are becoming resistantresistant to to antibiotics.antibiotics.