Transcript Bacteria and Viruses (Chapter 19)

Bacteria and Viruses
Chapter 19
Biology – Miller • Levine
What is a Virus?
From the Latin word for “poison”
 Particles of nucleic acid (DNA or RNA),
protein and occasionally lipids
 Various sizes and structures
 In order to reproduce, they must infect a
living cell

Virus Structures
Virus Structure
So small they can only be seen with a
powerful electron microscope
 A typical virus:

A core of either DNA or RNA
 A protein coat called a capsid that
surrounds the DNA or RNA
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Viral Infection
Viruses are very specific to the organism
they infect
 Plant viruses do not infect animal cells
 Animal viruses infect only certain
species of animal
 Bacteriophages – viruses that infect
bacteria (“bacteria eaters”)
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Lytic Infection
1.
2.
3.
4.
The virus injects its DNA or RNA into
the host cell.
The virus takes over the cell and
makes thousands of copies of itself.
The cell lyses, or bursts, and releases
the new viruses.
The new viruses go and infect more
cells.
Lytic Infection
Lysogenic Infection
1.
2.
3.
4.
A virus injects its DNA or RNA into the
host cell.
The viral DNA is inserted into the host
cell’s DNA, called a prophage.
Each time the cell reproduces, the viral
DNA is copied and passed on.
Eventually, the cell enters the lytic
cycle.
Lysogenic Infection
Viruses and Disease
Cause human diseases such as polio,
measles, AIDS, mumps, influenza,
rabies and the common cold
 Vaccine – a weakened or killed virus or
viral proteins that provides immunity
against a virus
 Oncogenic viruses – viruses that cause
cancer

Viruses and Disease
Retroviruses – viruses that contain
RNA as their genetic information
 They must produce DNA from their RNA
and then insert it into the host cell’s DNA
 HIV is a retrovirus
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Are Viruses Alive?

Yes…
Viruses reproduce
 They have DNA or RNA
 They evolve
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No…
They must reproduce inside a host cell
 They are not made of cells
 They do not have the other characteristics
of living things

Prokaryotes
Single-celled organisms that lack a
nucleus
 Used to be in a single kingdom – Monera
 Are now divided into two kingdoms:
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Eubacteria
Live almost anywhere
 Cell walls contain peptidoglycan
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Archaebacteria
Cell walls lack peptidoglycan
 Live in extremely harsh environments
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Identifying Prokaryotes
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Shapes
Bacilli – rod shaped
 Cocci – spherical
 Spirilla – spiral shaped
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Cell Walls
Gram-positive – appear purple
 Gram-negative – appear red
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Movement – flagella, wiggling, or don’t
move at all
Shapes of Prokaryotes
Obtaining Energy
Photoautotrophs – carry out
photosynthesis
 Chemoautotrophs – carry out
chemosynthesis
 Photoheterotrophs – capture sunlight for
energy, but feed on organic compounds for
nutrition
 Chemoheterotrophs – obtain their energy
and nutrition from organic compounds

Releasing Energy
Obligate aerobes – organisms that
require oxygen for respiration
 Obligate anaerobes – organisms that do
not require oxygen and may be poisoned
by it
 Facultative anaerobes – can survive with
or without oxygen

Growth and Reproduction
Binary fission – a type of asexual
reproduction where a bacterial cell divides
in half, producing identical “daughter” cells
 Conjugation – the exchange of genetic
information between two bacterial cells
 Endospore – when a bacterium forms a
tough wall that encloses the DNA & some
cytoplasm; allows it to survive harsh
conditions
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Conjugation
Bacteria in Nature
Decomposers – break down dead matter
into reusable nutrients
 Nitrogen fixers – convert nitrogen gas
into a form that is usable by plants
 Humans use bacteria to make certain
foods – yogurt, cheese, sour cream
 Can be used in industry to clean up
waste products & oil spills
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Bacteria and Disease
Pathogens – disease-causing agents
 Bacteria cause disease such as
tuberculosis, strep throat, pneumonia and
cholera
 Bacteria cause disease in one of two ways:
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Damage tissues by breaking them down for
food
 Release toxins (poisons) that harm the body
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Antibiotics – chemicals that block the
growth & reproduction of bacteria
Bacteria and Disease
Controlling Bacteria
Sterilization – destroys bacteria by
subjecting them either to great heat or to
chemicals
 Refrigeration can stop food from spoiling
due to bacteria
 Canning can be done to preserve food
for a long period of time
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