1. Chapter 19 Biology – Miller • Levine
Bacteria and Viruses
Chapter 19
Biology – Miller • Levine

2. 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

3. Virus Structures

4. 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

5. 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”)

6. Lytic Infection 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.

7. Lytic Infection

8. Lysogenic Infection 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.

9. Lysogenic Infection

10. 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

11. 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

12. Are Viruses Alive? Yes… No… Viruses reproduce They have DNA or RNA
They evolve
No…
They must reproduce inside a host cell
They are not made of cells
They do not have the other characteristics of living things

13. Prokaryotes Single-celled organisms that lack a nucleus
Used to be in a single kingdom – Monera
Are now divided into two kingdoms:
Eubacteria
Live almost anywhere
Cell walls contain peptidoglycan
Archaebacteria
Cell walls lack peptidoglycan
Live in extremely harsh environments

14. Identifying Prokaryotes
Shapes
Bacilli – rod shaped
Cocci – spherical
Spirilla – spiral shaped
Cell Walls
Gram-positive – appear purple
Gram-negative – appear red
Movement – flagella, wiggling, or don’t move at all

15. Shapes of Prokaryotes

16. 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

17. 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

18. 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

19. Conjugation

20. 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

21. 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:
Damage tissues by breaking them down for food
Release toxins (poisons) that harm the body
Antibiotics – chemicals that block the growth & reproduction of bacteria

22. Bacteria and Disease

23. 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