Bacteria and Viruses
Chapter 19
Bacteria & Viruses
19.1 Bacteria

Come in many shapes and sizes

Most common microorganisms are prokaryotes

Average size of 1-5 micrometers
–
Compared to eukaryotic cells that are 10-100
micrometers in diameter
2 Branches of Bacteria (Domains)

Archebacteria (similar to early Earth)
–
Confined to extreme environments
Methanogens - reduce CO2 to CH4
Extreme halophiles - salt loving
–
Thermoacidophiles
–
Similar to early earth
More closely related to eukaryotes than to modern
bacteria
–
–
–

Eubacteria (most modern)
–
very diverse
Bacterial Classification
Prokaryotic Phylogeny
Prokaryotic & Eukaryotic Cells
Classifying Prokaryotes

Eubacteria
–
–
–
–
–
Largest prokaryote Domain
Lack nuclei
Cell wall of a carbohydrate- Peptidoglycan
Cell membrane around cytoplasm
Some have an extra cell wall on the outside to resist
damage
Classifying Prokaryotes

Archaebacteria
–
–
–
–
Lack nuclei
Have cell walls without
peptidoglycan
Are chemically different
from Eubacteria
Many live in extremely
harsh environments
Bacteria Shapes
Identifying Prokaryotes

Shapes
–
–
–
Bacilli- Rod shaped
Cocci- Spherical shaped
Sprilla- spiral shaped
Colorized SEM 9,000
Colorized SEM 12,000
Identifying Prokaryotes

Cell walls
–
Gram staining used to tell them apart
–
Gram+ bacteria look purple
–
Gram- bacteria look pink
The Bacterial Cell Wall

Instead of cellulose, contain peptidoglycan
–


A polymer of modified sugars cross-linked with
amino acids
The gram stain distinguishes many disease
causing bacteria based on the type of cell wall
Many antibiotics work by attacking the
bacterial cell wall
The Gram Stain

Gram (+) Purple
–
–

accept gram stain
have simpler cell walls with large amounts of
peptidoglycan
Gram (-) Pink
–
–
–
–
–
do not stain
have more complex cell walls with less peptidoglycan
cell walls contain lipopolysaccharides
are more likely to be pathogenic (cause disease)
more resistant to antibiotics
Cell Wall & Gram Stain
Gram (+) & Gram (-)
Gram (+)Purple & Gram (-)Pink
Identifying Prokaryotes

Movement
–
Flagella
–
Lash, snake or spiral forward
–
They do not move at all
Motility (movement)


About half are capable of directional movement.
3 mechanisms:
–
–
–

flagella - different from eukaryotes
spiral shaped bacteria (spirochetes) have a filament
that spirals around the cell under the outer sheath
some bacteria secrete slimy chemicals & glide
Taxis
–
–
movement toward or away from a stimulus
many bacteria exhibit this form of movement
Structures of
Movement
Structure of Prokaryotic Flagella
Metabolic Diversity

Heterotrophs
–
Chemoheterotrophs: must take in organic molecules
for energy and carbon
–
Photoheterotrophs: Use sunlight for energy but
need organic compounds for a carbon source
Metabolic Diversity

Autotrophs
–
Chemoautotrophs: perform chemosynthesis to
make carbon from carbon dioxide. Does not require
sunlight
–
Photoautotrophs: use light to convert carbon dioxide
and water into carbon compounds and oxygen gas.
Getting Energy

Bacteria need a constant supply of energy

Obligate aerobes- require constant supply of oxygen

Obligate anaerobes- need no oxygen, for some
oxygen will kill it

Facultative anaerobes- survive with or with out
oxygen
Growth and Reproduction

Binary fission (to split)

Conjugation

Spore formation
Binary Fission
Bacterial Conjugation
Endospores (example: Anthrax)

Some bacteria form resistant cells called

Resist extremes of temperature, pH, etc.
endospores (11,000 year old spores found)
Importance of Bacteria



Only a minority cause disease
Many are essential to life on earth
Decomposers
–

Nitrogen Fixers
–


Break down dead matter
Converts nitrogen into a form plants can use
Humans use Bacteria
Often live in symbiotic relationships with other
organisms
19.2 Viruses

What is a virus?
–
Particles of nucleic acid and proteins
–
Core made up of DNA or RNA surrounded by a
capsid
Head
–
Need to infect a
living host to reproduce
Tail
Tail fiber
DNA
Viral Structure
Bacteriophage
Are Viruses Alive?






Viruses contain nucleic acids & proteins
Viruses, by themselves, cannot make or use food, grow
or reproduce
Some scientists believe viruses were never
independently living organisms
Others believe viruses evolved from simple bacteria like
mycoplasmas & rickettsiae
Another hypothesis: viruses are genes that have
escaped from the genomes of living cells
Not much evidence to support any one of these
Viral Infection

Lytic Cycle
–
–
–
–
–
–
Virus attaches to host cell
Injects its DNA
Host makes RNA from viral DNA
Cell begins to make copies of virus
New viruses form
Host cell bursts
Lytic Cycle of the T4 Phage
Viral Infection

Lysogenic Cycle
–
–
–
–
–
Virus attaches to host cell
Injects DNA
Viral DNA incorporates itself into the host DNA
Viral DNA can be dormant
Once it becomes active, it follows the 4 processes in
the lytic cycle
Lytic and Lysogenic Cycle (video)

http://www.youtube.com/watch?v=gU8XeqI7yts
&feature=related
Phage Lytic and
Lysogenic Cycles
Viral Infection

Retrovirus: Genetic information is RNA
–
Produces DNA copy and creates a prophage
Envelope
–
Example:
HIV/AIDS
Glycoprotein
Protein coat
RNA (two
identical strands)
Reverse transcriptase
19.3 Diseases Caused by
Bacteria and Viruses

Pathogens- disease causing agents

Bacterial Disease

Viral Diseases
Diseases Caused By Bacteria

How does bacteria produce disease?
–
Damage the cells and tissues by breaking down the
cells for food
–
Releasing toxins (poisons into the body)
Preventing Diseases

Vaccines

Immunity

Antibiotics
Controlling Bacteria

Sterilization

Disinfectants

Proper food storage
Diseases Caused by Viruses

Viruses disrupt the body’s normal equilibrium

Cannot be treated with antibiotics

Viruses can infect humans and plants
Virus-like Particles (Viroids)

Viroids- single stranded RNA molecule with no
capsid
–
They cause diseases in plants
–
Infect cell and produce more viroids by disrupting
the plant metabolism
Virus-like Particles (Prions)

Prions- contain only protein; no DNA or RNA
–
They cause diseases in animals and humans
–
Prions clump and cause normal protein to clump
with it- creating new prions
Prion Action
Chapter 19
Viruses and Bacteria
Multiple Choice Practice
Questions
19–1
–Which
characteristic distinguishes eubacteria from
archaebacteria?




Eubacteria lack peptidoglycan in their cell walls.
Eubacteria contain peptidoglycan in their cell walls.
Eubacteria lack a nucleus.
Eubacteria do not possess mitochondria.
19–1
–Which
characteristic distinguishes eubacteria from
archaebacteria?




Eubacteria lack peptidoglycan in their cell walls.
Eubacteria contain peptidoglycan in their cell walls.
Eubacteria lack a nucleus.
Eubacteria do not possess mitochondria.
19–1
–
Rod-shaped prokaryotes are called




bacilli.
cocci.
spirilla.
streptococci.
19–1
–
Rod-shaped prokaryotes are called




bacilli.
cocci.
spirilla.
streptococci.
19–1
–
Bacteria that must live without oxygen are called




obligate aerobes.
facultative anaerobes.
obligate anaerobes.
facultative aerobes.
19–1
–
Bacteria that must live without oxygen are called




obligate aerobes.
facultative anaerobes.
obligate anaerobes.
facultative aerobes.
19–1
–
Prokaryotes that make their own food molecules
from carbon dioxide and water but live where there
is no light are called




photoautotrophs.
photoheterotrophs.
chemoautotrophs.
chemoheterotrophs.
19–1
–
Prokaryotes that make their own food molecules
from carbon dioxide and water but live where there
is no light are called




photoautotrophs.
photoheterotrophs.
chemoautotrophs.
chemoheterotrophs.
19–1
–
Bacteria that attack and digest the tissue of dead
organisms are called




decomposers.
nitrogen fixers.
chemoautotrophs.
archaebacteria.
19–1
–
Bacteria that attack and digest the tissue of dead
organisms are called




decomposers.
nitrogen fixers.
chemoautotrophs.
archaebacteria.
19–2
–
Viruses that contain RNA as their genetic
information are known as




prions.
oncoviruses.
retroviruses.
bacteriophage.
19–2
–
Viruses that contain RNA as their genetic
information are known as




prions.
oncoviruses.
retroviruses.
bacteriophage.
19–2
–
The first type of virus to be studied was the




bacteriophage.
tobacco mosaic virus.
influenza virus.
AIDS virus.
19–2
–
The first type of virus to be studied was the




bacteriophage.
tobacco mosaic virus.
influenza virus.
AIDS virus.
19–2
–Which




of the following statements about viruses is true?
Viruses appear similar to bacteria when studied with a light
microscope.
Viruses display the essential characteristics of living things.
Viruses can reproduce independently if they contain DNA.
Viruses cannot reproduce unless they infect a living cell.
19–2
–Which




of the following statements about viruses is true?
Viruses appear similar to bacteria when studied with a light
microscope.
Viruses display the essential characteristics of living things.
Viruses can reproduce independently if they contain DNA.
Viruses cannot reproduce unless they infect a living cell.
19–2
–
A virus integrates its DNA into the DNA of the host
cell but remains inactive for a while in




a lytic infection.
a lysogenic infection.
neither a lytic nor a lysogenic infection.
retroviral infection.
19–2
–
A virus integrates its DNA into the DNA of the host
cell but remains inactive for a while in




a lytic infection.
a lysogenic infection.
neither a lytic nor a lysogenic infection.
retroviral infection.
19–2
–
Retroviruses are considered unique because




they have RNA in their capsid and not DNA.
they have DNA in their capsid and not RNA.
after infection of a host cell, their RNA makes DNA.
after infection of a host cell, their DNA makes RNA.
19–2
–
Retroviruses are considered unique because




they have RNA in their capsid and not DNA.
they have DNA in their capsid and not RNA.
after infection of a host cell, their RNA makes DNA.
after infection of a host cell, their DNA makes RNA.
19–3
–Biologists




know that bacteria can cause human disease by
entering cells and using the cell to make new bacteria.
producing toxic substances that interfere with normal cell functi
decomposing the remains of dead organisms.
changing atmospheric nitrogen into nitrogen compounds.
19–3
–Biologists




know that bacteria can cause human disease by
entering cells and using the cell to make new bacteria.
producing toxic substances that interfere with normal cell functio
decomposing the remains of dead organisms.
changing atmospheric nitrogen into nitrogen compounds.
19–3
–
A process that destroys bacteria by subjecting them
to great heat is known as




refrigeration.
sterilization.
pickling.
boiling.
19–3
–
A process that destroys bacteria by subjecting them
to great heat is known as




refrigeration.
sterilization.
pickling.
boiling.
19–3
–
Which of the following diseases is transmitted by a
mosquito bite?




influenza
measles
West Nile virus
chickenpox
19–3
–
Which of the following diseases is transmitted by a
mosquito bite?




influenza
measles
West Nile virus
chickenpox
19–3
–
Which of the following diseases is thought to be
caused by prions?




diphtheria
mad cow disease
tuberculosis
smallpox
19–3
–
Which of the following diseases is thought to be
caused by prions?




diphtheria
mad cow disease
tuberculosis
smallpox
19–3
–
The best way to combat viral diseases is




to use antibiotics.
to treat individual symptoms.
to use preventive vaccines.
to let the disease “cure itself.”
19–3
–
The best way to combat viral diseases is




to use antibiotics.
to treat individual symptoms.
to use preventive vaccines.
to let the disease “cure itself.”