Bio 100 Chapter 16

Chapter 16Evolution of

Microbial LifeLecture Outline

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

16.1 Viruses have a simple structure

Viruses are noncellular /nonliving

Size comparable to large protein macromolecule Ranging from 0.2 to 2 μm

Basic anatomy of a Virus Outer capsid composed of protein

May be surrounded by outer membranous envelope

Inner core of nucleic acid (DNA or RNA)16-2

Figure 16.1A Adenovirus, a naked virus, with a polyhedral capsid and a fiber at each corner

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protein unit

capsid

fiber

TEM 80,000×

DNA

(Right): © Dr. Hans Gelderblom/Visuals Unlimited

Figure 16.1B Influenza virus, surrounded by an envelope with spikes

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capsid

spikeenvelope

20 nm

RNA

(Right): © K.G. Murti/Visuals Unlimited

Classification of Viruses:1. Their type of nucleic acid – DNA or RNA

2. Whether nucleic acid is single-stranded or double-stranded

3. Size and shape

4. Presence or absence of an outer membrane

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16.2 Some viruses reproduce inside bacteria

Bacteriophages (phages) Viruses that infect bacteria

Two types of life cycles Lytic cycle

Most common 5 stages

Lysogenic cycle Phage becomes latent – called prophage Environmental factors trigger entry into lytic cycle

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Figure 16.2 The lytic and lysogenic cycles in prokaryotes

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1

5 2a

34

bacterialcell wall

nucleic acid

bacterialDNA

capsid

ATTACHMENTCapsid combines with receptor.

RELEASENew viruses leave host cell.

PENETRATIONViral DNA enters host.

viralDNA

prophage

daughter cells

capsid

viralDNA

BIOSYNTHESISViral components are synthesized.

MATURATIONViral components are assembled.

LYTICCYCLE

LYSOGENICCYCLE

2b

viralDNA

INTEGRATION Viral DNA isintegrated into bacterial DNAand then is passed on whenbacteria reproduce.

16.3 Plant diseases caused by Viruses

Most plant viruses are RNA viruses

Generalized symptoms Stunted growth; discoloration of leaves, flowers, and fruits; death

of stems, leaves, and fruits; irregularities in fruit size; etc.

Viruses seldom kill their plant hosts

Spread by variety of mechanisms

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Figure 16.3A The tobacco mosaic virus (TMV) is responsible for discoloration in the leaves of tobacco plants

Figure 16.3B A virus is responsible for the variegation and streaking in Rembrandt tulips

Viruses used intentionally to produce streaking

Weakens plant and it does not live long

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HOW BIOLOGY IMPACTS OUR LIVES

16A Humans Suffer from Emergent Viral Diseases

Emergent diseases – newly recognized as infectious

Viruses are constantly in a state of evolutionary flux Can acquire new spikes to allow entry into new cells

Virus that cannot pass from human to human after jumping from an animal host will not be capable of causing an epidemic A large-scale infection of many persons

Some emergent diseases are transmitted by vectors Mosquitoes used by several viral diseases

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16A Humans Suffer from Emergent Viral Diseases

H1N1 virus Usually found in pigs, in humans it causes the symptoms of flu Named after spikes H1 and N1

Severe acute respiratory syndrome (SARS) Causes high fever, body aches, and pneumonia

Avian influenza (or bird flu) Disease does not often spread from chickens to humans, nor is

it efficiently transmitted among humans Ebola

1 of a number of viruses that cause hemorrhagic fever Highly contagious and fatal Vector and animal reservoir unknown

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16.4 Viruses reproduce inside animal cells and cause diseases

Life cycle of a DNA virus in animals and humans Attachment: Glycoprotein spikes projecting through

the envelope allow the virus to bind to host cells Penetration: After the viral particle enters the host

cell, uncoating follows and viral DNA enters the host Biosynthesis: The capsid and other proteins are

synthesized by host cell ribosomes according to viral DNA instructions

Maturation: Viral proteins and DNA replicates are assembled to form new viral particles

Release: In an enveloped virus, budding occurs and the virus develops its envelope

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Figure 16.4 Replication of an animal virus

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ER

Attachment: Spikecombines with receptor.

1

capsid

Cytoplasm

nuclearpore

nucleicacid (DNA)

plasmamembrane

spike

Biosynthesis: Viralproteins are synthesized.

3a

viral mRNA

capsidprotein

Biosynthesis:Many strands ofDNA are produced.

Nucleus

viral DNA

3b

envelope

Penetration: Virusenters cell, anduncoating occurs.

2

uncoating

ribosome

Figure 16.4 Replication of an animal virus(Cont.)


capsid

viral spikes

Release: Budding givesvirus an envelope.

5

4 Maturation: Viralcomponents areassembled.

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16.5 HIV (the AIDS virus) is a retroviruses

Genome consists of RNA, instead of DNA Retrovirus

Uses reverse transcription from RNA into DNA in order to insert a complementary copy of its genome into the host’s genome

Uses reverse transcriptase enzyme

HIV provirus Viral DNA integrated into host DNA. Usually transmitted to another person by means of cells that

contain proviruses

Emergent viral disease that jumped from chimpanzees to humans

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Figure 16.5 Reproduction of HIV

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ribosome

reverse transcriptase

capsid

spike

envelope

receptor

Reverse transcription

Penetration

Replication

Attachment

ER

Biosynthesis

1

2

3

4

5

viral RNA

cDNA

nuclearpore

viralmRNA

hostDNA

provirus

viralenzyme

Integration


Figure 16.5 Reproduction of HIV (Cont.)

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ribosome

Replication

ER

spike

Biosynthesis

Maturation

Release

5

6

7

viralmRNA

hostDNA

provirus

viralenzyme

capsidprotein

Integration

viral RNA

4


Prions

Prions Protein infectious particles

Misfolded proteins whose presence causes other proteins to also become misfolded

Cause rare but serious brain diseases, such as Creutzfeldt-Jakob Disease (CJD)

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Figure 16B.1 A virus is less complex than a prokaryote, because all it takes is a capsid surrounding a genetic material. Like this one, some viruses use RNA as their genetic material


caspid

protein unit

RNA

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Figure 16B.2 A prokaryote is more complex, both metabolically and structurally, than a virus. Like this one, prokaryotes always use DNA as their genetic material


DNA

plasmamembrane

cellwall

phospholipidbilayer

enzymaticproteins

ribosomes

Figure 16.6B Chemical evolution at hydrothermal vents

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plume of hot waterrich in iron sulfides

hydrothermalvent

© Ralph White/Corbis

16.9 Prokaryotes have unique structural features

Bacteria & Archaea are in separate domains due to molecular and cellular differences

Unicellular organisms / Prokaryotic Lack a eukaryotic nucleus and membranous

organelles Nucleoid – dense area with a single chromosome May have plasmids – accessory rings of DNA

Cell wall strengthened by peptidoglycan May have capsule or slime layer

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16.9 Prokaryotes have unique structural features

Appendages: Pili – short, for attachment Flagella – longer, for movement

Three Basic Shapes of Prokaryotes Cocci (sing., coccus) – round or spherical Bacilli (sing., bacillus) – rod-shaped Spirilla (sing., spirillum) – spiral- or helical-shaped

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Figure 16.9A Anatomy of bacterium

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flagella

pili

1 µmribosome

nucleoid

plasma membrane

cell wall

capsule

(bacterium, whole): © Ralph A. Slepecky/Visuals Unlimited; (bacterium, circle): Courtesy Harley W. Moon, U.S. Dept. of Agriculture

Figure 16.9B The three shapes of bacteria

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16.10 Prokaryotes reproduce by binary fission

Reproduce asexually using binary fission Results in two prokaryotes of equal size Genetically identical (but higher mutation rate) Not mitosis Three steps:

1. DNA replication 2. Chromosome segregation 3. Cytokinesis

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Figure 16.10 Binary fission results in two bacteria

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DNA replication1

Chromosome segregation2

3 Cytokinesis

Daughter cells

Figure 16.10 Binary fission results in two bacteria (Cont.)

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cytoplasm

cell wall

nucleoid

Cytokinesis

0.5 µm© CNRI/SPL/Photo Researchers, Inc.

Some bacteria form Endospores

When faced with unfavorable environmental conditions, some bacteria form endospores

A portion of the cytoplasm and a copy of the chromosome dehydrate and are then encased by a heavy, protective spore coat

Spores survive in the harshest of environments and for very long periods of time

Not a means of reproduction

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endospore

© Alfred Pasieka/SPL/Photo Researchers, Inc.

endospore withinClostridium tetani.

16.11 Gene are transfer between bacteria

1. Transformation Recipient picks up “free DNA” from its surroundings

2. Conjugation Donor bacterium passes DNA to the recipient by way

of a conjugation pilus Plasmid – small circle of DNA

3. Transduction Bacteriophages carry portions of bacterial DNA from a

donor cell to a recipient

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Figure 16.11A Gene transfer by transformation

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donor cell recipient cell

DNALysis ofdonor cellreleasesDNA.

Donor DNA is taken up by recipient.

Figure 16.11B Gene transfer by conjugation

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DNA

donor cellplasmid

Donor DNA is transferred directly torecipient through a conjugation pilus.

Figure 16.11C Gene transfer by transduction

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Bacteriophageinfects a cell.

Donor DNAis picked up bybacteriophage

Donor DNAtransferred when bacteriophageinfects recipient.

Prokaryotes have various means of nutrition

Obligate Anaerobes Unable to grow in the presence of free oxygen A few serious illnesses – such as botulism, gas

gangrene, and tetanus – are caused by anaerobic bacteria

Facultative anaerobes Able to grow in either presence or absence of oxygen

Most prokaryotes are aerobic and require a constant supply of oxygen

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Autotrophic Prokaryotes Produce their own organic nutrients / “self-feeding”

Photoautotrophs Use solar energy to reduce carbon dioxide to organic

compounds

Chemosynthetic Remove electrons from inorganic compounds use them to

reduce CO2 to an organic molecule

Ex: Bacteria in a hydrothermal vent

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Figure 16.12A Some anaerobic photosynthetic bacteria live in the muddy bottoms of eutrophic lakes

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Figure 16.12B Some chemosynthetic prokaryotes live at hydrothermal vents

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© Science VU/Visuals Unlimited

clamclam

tubeworm

Heterotrophic Prokaryotes (“other feeding”) Take in organic nutrients Saprophytic bacteria

Ex: Decomposers in soil

Symbiosis: Two different species living together. Mutualism – both species benefit Commensalism– one species benefits, no effect on

the other species. Parasitism – one species benefits, one is harmed.

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16.13 The cyanobacteria are ecologically important organisms

Pigments occur in the membrane of flattened disks called thylakoids

Perform photosynthesis like plants Believed to be responsible for introducing

oxygen into the atmosphere Some possess heterocysts for nitrogen fixation Common in water, soil, and moist surfaces Some are symbiotic with other organisms

(e.g. lichens are cyanobacteria and fungi)

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16-43FIGURE 16.13 Diversity among the cyanobacteria


Gloeocapsa, a unicellular form Oscillatoria, a filamentous formAnabaena, a colonial form

heterocyst

Oscillatoria cell

storagegranule

thylakoids

DNA

cell wall

plasmamembrane

(Gloeocapsa): © Runk/Schoenberger/Grant HeilmanPhotography; (Anabaena): © Philip Sze/Visuals Unlimited; (Oscillatoria): © Tom Adams/Visuals Unlimited

16.14 Archaea live in extreme environments

Structure and Function No peptidoglycan in cell wall

Ex: Methanogens-produce methane from the decomposition of organic matter

Archaea are found in extreme environments Halophiles-organism that requires a salty environment

Thermoacidophiles-environments are extremely acidic with high temperatures

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Figure 16.14A Methanogen habitat and structure 16-45


(swamp): © altrendonature/Getty Images; (inset): © Ralph Robinson/Visuals Unlimited

Methanosarcinamazei

Figure 16.14B Halophile habitat and structure

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(Great Salt Lake): © John Sohlden/Visuals Unlimited; (inset): FromJ.T. Staley, et al., Bergey's Manual of Systematic Bacteriology, Vol. 13, © 1989Williams and Wilkins Col, Baltimore. Prepared by A.L. Usted Photography by Dept. of Biophysics, Norwegian Institute of Technology

Halobacteriumsalinarium

Great SaltLake, Utah

Figure 16.14C Thermoacidophile habitat and structure

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(geysers): © JeffLepore/Photo Researchers, Inc.; (inset): Courtesy Dennis W. Grogan, University of Cincinnati

Sulfolobusacidocaldarius

Boiling springs and geysers inYellowstone National Park

16.15 Prokaryotes have medical and environmental importance

Vast majority of bacterial species are not pathogenic to humans

Some bacteria are pathogenic

Tuberculosis (TB) kills more people worldwide than any other infectious disease

Caused by Mycobacterium tuberculosis

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Prokaryotes are important in the environment

Ancient photosynthetic cyanobacteria released copious amounts of oxygen

Bacteria break down and recycle nutrients in the soil

Prokaryotes play an essential role in the carbon nitrogen, sulfur, and phosphorus environmental cycles

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16D Disease-causing Microbes Can Be Biological Weapons

Biological warfare is the use of viruses and bacteria, or their toxins, as weapons of war

Bioterrorists prefer pathogens that are Highly contagious, consistently produce a desired

detrimental effect on a population, have a short incubation period, and are easy to disseminate and deliver to a population

In addition to humans, valuable animals and crops can be the targets of biological attacks

Vaccines and preventives may be the best way to counter biological agents

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Connecting the Concepts:Chapter 16

Viruses are noncellular, disease-causing agents

Prokaryotes are cellular, but their structure is simpler than that of eukaryotes

Many prokaryotes can live in extreme environments.

Not all bacteria cause diseases, but the few that do infect humans can be deadly.

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Bio 100 Chapter 16

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