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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
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
The Gram Stain
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
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
Motility (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
Some bacteria form resistant cells called endospores (11,000 year old spores found)
Resist extremes of temperature, pH, etc.
Endospores (example: Anthrax)
Importance of Bacteria
Only a minority cause disease Many are essential to life on earth Decomposers
– Break down dead matter Nitrogen Fixers
– 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
– Need to infect a
living host to reproduce
Head
Tail
Tail fiber
DNA
300,
000
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
– Example:
HIV/AIDS
Envelope
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 19Viruses 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.”