VIRUSES, BACTERIA &

ARCHAEA

VIRUSES

Viruses are non-living infectious particles

Lack cellular organization

Lack growth

Lack metabolic abilities

Energy production

Waste generation

Require a host cell for replication

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Viral Structure

Nucleic acid in a protein coat

Nucleic acid can be DNA or RNA

Protein coat = capsid

May be surrounded by an envelope

Size

~10-200 nm

Slide 17

Fig. 22.16, p. 364

viral RNA

protein subunits of coat

18-nm diameter,

250-nm length 80-nm diameter

lipid envelope; proteins span the envelope, line its inner surface, and spike out above it

viral RNA

reverse transcriptase

viral coat (proteins)

100-120 nm diameter

DNA

protein coat

sheath

base plate

tail fiber

65-nm diameter head,

225-nm total length 3

Examples of viruses

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Tobacco mosaic virus Bacteriophage

Influenzavirus

Adenovirus

Herpesvirus

Quick Quiz: True or false: A virus is a

living organism.

A) True

B) False

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Quick Quiz: A virus is not considered a

living organism because it cannot do

which of these functions?

A) Grow

B) Reproduce

C) Metabolize

D) Respond to their environment

E) All of the above

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Viral Replication

Steps in Viral Replication:

Attachment to host cell

Penetration of host cell

Replication and synthesis of nucleic acids

and proteins

Assembly of viral components

Release of new viral particles

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Viral Replication

Steps in Viral Replication:

Attachment to host cell

Penetration of host cell

Replication and synthesis of nucleic acids

and proteins

Assembly of viral components

Release of new viral particles

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Figure 20-5 p326

A4 Viral enzyme excises viral DNA from chromosome.

C Viral proteins self-assemble into a coat around viral DNA.

D Accessory parts are attached to viral coat.

B Host replicates viral genetic material, builds viral proteins.

A3 Cell divides; recombinant DNA in each descendant cell.

A2 Chromosome and integrated viral DNA are replicated.

Lysogenic

Pathway

Lytic

Pathway

A1 Viral DNA is inserted into host chromosome by viral enzyme action.

A Viral particle binds, injects genetic material. E Lysis of host cell lets

new viral particles escape.

Reproduction of Bacteriophage

Reproductive cycles

Lytic vs. lysogenic cycles

Quick Quiz: True or false: During the

lysogenic cycle, a virus’s DNA is

incorporated into a host cell’s genome.

A) True

B) False

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(following animation)

Quick Quiz: My mom just got shingles,

which is a localized recurrence of the

chickenpox virus, varicella zoster. If

you have chickenpox as a child, then

you can get shingles as an adult.

Which cycle does varicella zoster use?

A) Lytic

B) Lysogenic

C) Both lytic and lysogenic

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Replication of DNA Viruses of

Plants & Animals

Examples

Polio, rabies, chickenpox, herpes, influenza

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Replication of RNA Viruses

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VIROIDS & PRIONS

Viroids

Infectious RNA

Cause of Hepatitis D

Prions

Infectious proteins

Kuru

Scrapie

CJD (Creutzfeldt-Jakob disease)

Bovine spongiform encephalopathy (“mad

cow”): variant CJD (vCJD)

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Quick Quiz: Which of the following is a

living organism?

A) Virus

B) Prion

C) Prokaryote

D) Viroid

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Quick Quiz: Why was “prokaryote” the

right choice on the previous slide?

A) It is the only one that has DNA

B) It is the only one that is cellular

C) It is the only one that has proteins

D) All of the above

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PROKARYOTES

Taxonomy

Domain: Archaea Bacteria

Kingdom: Archaebacteria Eubacteria

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Prokaryotic vs. Eukaryotic Cells

Component Prokaryote Eukaryote

Plasma membrane yes yes

Cell wall most some

DNA circular linear

Nucleus no (nucleoid) yes

Membrane-bound no yes

organelles

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General Characteristics of Prokaryotes

Unicellular

Unique cell structure & organization

Extremely diverse metabolic abilities

Most abundant organisms on the planet

Found in every habitat

Most are beneficial or benign

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Size

Range: 0.2 m – 5 mm (length)

Most ~ 1 m or smaller

Slide 1

Fig. 22.1, p. 354

100 µm 20 µm 0.5 µm

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Categorization of Prokaryotes

Cell shape

Cell wall properties

Thick – gram positive

Thin – gram negative

Metabolic abilities

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Prokaryote structure

Shape

Coccus (cocci)

Bacillus (bacilli)

Spirillum (spirochete)

Organization

Single

Chains

Clusters

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Gram-negative

Gram-positive

Metabolic Classes

Two ways to categorize organisms

metabolically

What is our carbon source?

Autotrophs

Heterotrophs

What is our energy source?

Phototrophs

Chemotrophs

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Metabolic Classes

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Metabolic Classes

Third way to categorize organisms

metabolically

How does the organism handle O2?

Aerobe – requires oxygen

Obligate anaerobe – cannot survive in oxygen

Facultative anaerobe – doesn’t need it, but can live

with it

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Quick Quiz: Prokaryotes may get their

energy in which of the following ways?

A) From the sun

B) From chemicals

C) From carbon dioxide

D) A and B

E) A and C

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Quick Quiz: You are a scientist who

has discovered a new kind of

prokaryote that lives deep in the

ocean, where it’s dark. What can you

definitely say about this organism?

A) It’s an autotroph

B) It’s a heterotroph

C) It’s a chemotroph

D) It’s a phototroph

E) It’s a photoautotroph

F) It’s a chemoheterotroph

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Fig. 21-8b, p. 340

cytoplasm,

with ribosomes

DNA, in

nucleoid region

pilus

flagellum

outer capsule

cell wall

plasma membrane

Prokaryote structure

Reproduction

Asexual

Binary fission

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Gene transfer

“Horizontal” gene transfer

Conjugation from other bacteria

Transduction from viruses

Transformation – naked DNA from environment

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sex pilus

Fig. 21-11, p. 341

nicked plasmid conjugation tube

Quick Quiz: Which of the following

processes does a bacterium use to

reproduce?

A) Conjugation

B) Binary fission

C) Transduction

D) Transformation

E) Infection

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Quick Quiz: If binary fission is

analogous to a couple having a baby,

then gene transfer is analogous to…

A) Cousins having a baby together

B) A person donating bone marrow to a stranger

C) Adopting a baby from a stranger

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Types of Eubacteria

Nitrogen fixers

N fixers nitrifiers denitrifiers

N2 ammonia nitrites & nitrates N2

Food fermentations

Lactic acid bacteria (e.g., lactobacilli)

Cheese, yogurt, pickles, sauerkraut

Pathogens

Salmonella enteritidis

Staphylococcus aureus

Clostridium botulinum

Streptococcus pyogenes 33

Types of Eubacteria

Thermophiles

“Heat lovers” – Thermus aquaticus

Cyanobacteria

Photosynthetic, produce atmospheric oxygen

Proteobacteria

Large, diverse group of bacteria

Gram-positive heterotrophs

Many produce endospores and/or toxins

Spirochetes & chlamydia

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Types of Archaebacteria

Extreme environments

Chemoautotrophs

Obtain energy from inorganic compounds

Examples:

Methanogens

Extreme thermophiles

Extreme halophiles

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Quick Quiz: Pathogens causing strep

throat, staph infections, and

salmonella food poisoning are…

A) Eubacteria

B) Archaebacteria

C) Prions

D) Viruses

E) All of the above

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Quick Quiz: Pathogens causing strep

throat, staph infections, and

salmonella food poisoning are…

A) Eubacteria

B) Archaebacteria

C) Prions

D) Viruses

E) All of the above

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