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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 lipidsVarious sizes and structuresIn 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 RNAA protein coat called a capsid that
surrounds the DNA or RNA
Viral Infection
Viruses are very specific to the organism they infect
Plant viruses do not infect animal cellsAnimal viruses infect only certain
species of animalBacteriophages – viruses that infect
bacteria (“bacteria eaters”)
Lytic Infection
1. The virus injects its DNA or RNA into the host cell.
2. The virus takes over the cell and makes thousands of copies of itself.
3. The cell lyses, or bursts, and releases the new viruses.
4. The new viruses go and infect more cells.
Lytic Infection
Lysogenic Infection
1. A virus injects its DNA or RNA into the host cell.
2. The viral DNA is inserted into the host cell’s DNA, called a prophage.
3. Each time the cell reproduces, the viral DNA is copied and passed on.
4. 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
Are Viruses Alive?
Yes…Viruses reproduceThey have DNA or RNAThey evolve
No…They must reproduce inside a host cellThey are not made of cellsThey do not have the other characteristics
of living things
Prokaryotes
Single-celled organisms that lack a nucleus
Used to be in a single kingdom – MoneraAre now divided into two kingdoms:
EubacteriaLive almost anywhereCell walls contain peptidoglycan
ArchaebacteriaCell walls lack peptidoglycanLive in extremely harsh environments
Identifying Prokaryotes
ShapesBacilli – rod shapedCocci – sphericalSpirilla – spiral shaped
Cell WallsGram-positive – appear purpleGram-negative – appear red
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
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
Bacteria and Disease
Pathogens – disease-causing agentsBacteria cause disease such as
tuberculosis, strep throat, pneumonia and cholera
Bacteria cause disease in one of two ways:Damage tissues by breaking them down for
foodRelease toxins (poisons) that harm the body
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