1. Chapter 20
Viruses and Bacteria
Section 1: Viruses
Section 2: Bacteria

2. Section 1
Viruses
Objectives:
Describe why a virus is not considered a living organism.
Summarize the discovery of the tobacco mosaic virus.
Describe the basic structure of a virus.
Summarize the steps of viral replication.
Explain how HIV infects immune system cells.

3. Viruses Is a Virus Alive?
Section 1
Viruses
Is a Virus Alive?
Viruses do not have all the characteristics of life and are therefore not considered to be alive.
Viruses do not grow, do not have homeostasis and do not metabolize.
Viruses are pathogens-agents that cause disease.

4. Viruses Viral Structure
Section 1
Viruses
Viral Structure
Viruses consist of segments of a nucleic acid (DNA or RNA) contained in a protein coat, or capsid, and some have an envelope. It consists of lipids, and glycoproteins, which are proteins attached to carbohydrate molecules

5. Viruses Viral Reproduction
Section 1
Viruses
Viral Reproduction
Viruses replicate inside living cells. They enter a cell by injecting their genetic material into the cell, by slipping through tears in the plant cell wall, or by binding to molecules on the cell surface and triggering endocytosis.
Lytic Cycle In bacteria viruses, the cycle of viral infection, replication, and cell destruction is part of the lytic cycle.
Lysogenic Cycle In the lysogenic cycle, the viral genome replicates without destroying the host cell.

7. Viruses Viral Reproduction continued
Section 1
Viruses
Viral Reproduction continued
Host Cell Specificity Viruses are often species specific.
Structure of HIV—an Enveloped Virus HIV replicates inside only human immune system cells, specifically white blood cells.

8. Viruses How HIV Infects Cells
Section 1
Viruses
How HIV Infects Cells
Attachment HIV binds to human immune cells that contain CD4 receptors.
Entry into Macrophages Macrophages contain CD4 receptors and CCR5 co-receptors, and this allows HIV to enter these cells.
Replication HIV replicates inside the host macrophage, but does not kill the cell. Instead, the new viruses are released from the host by budding.
AIDS HIV infection leads to the destruction of the body’s T cells and weakens the immune system. This can lead to AIDS.

10. Viruses Viral Diseases Section 1
Emerging viruses are geographically isolated viruses that cause disease in humans.
Other classes of pathogens:
Prions are infectious proteins that cause disease in certain animals. They are composed of proteins but have no nucleic acid. They cause normal proteins to misfold.
Viroids are infectious RNA molecules that cause disease in plants. They are a single strand of RNA that has no capsid.

12. Section 2
Bacteria
Objectives:
List seven differences between bacteria and eukaryotic cells.
Describe three different ways bacteria can obtain energy.
Describe the external and internal structure of Escherichia coli.
Distinguish two ways that bacteria cause disease.
Identify three ways that bacteria benefit humans.

13. Bacteria Bacterial Structure Section 2
Characteristics of Bacteria Bacteria differ from eukaryotes in their
Internal compartmentalization-no nucleus
Cell size-typically much smaller
Multicellularity-all bacteria are single cells
Chromosomes-circular in shape
Reproduction-binary fission
Flagella-simple structures composed a single protein fiber
Pili-shorter, thicker outgrowths that allow bacteria to attach to surfaces
Metabolic diversity-Anaerobic and Aerobic processes

14. Bacterial Cell Shapes A bacteria is one of three shapes: rod-shaped (bacillus), round-shaped (coccus), and spiral-shaped (spirillum)

15. Bacteria Bacterial Structure continued
Section 2
Bacteria
Bacterial Structure continued
Bacteria can be classified according to their cell wall structure. Gram staining can be used to distinguish these two groups.
Gram positive
Gram negative
Antibiotics are chemicals that interfere with the life processes in bacteria. Gram staining determines which antibiotics are most effective.

17. Key Terms:
Capsule: a gel-like layer found outside the cell wall and membrane.
Endospores: a thick walled protective spore that forms inside a bacterial cell and resists harsh conditions.
Conjugation: a process in which two organisms exchange genetic material.

19. Bacteria Obtaining Energy
Section 2
Bacteria
Obtaining Energy
Photosynthetic bacteria can be classified into four major groups: purple nonsulfur bacteria, green sulfur bacteria, purple sulfur bacteria, and cyanobacteria.
Green sulfur and Purple sulfur grow in anaerobic conditions.
Chemoautotrophs obtain energy by removing electrons from inorganic molecules such as ammonia, hydrogen sulfide, or methane.
Most bacteria are heterotrophs and many are aerobic.

20. Bacteria Pathogenic Bacteria
Section 2
Bacteria
Pathogenic Bacteria
Bacteria can cause disease by metabolizing nutrients in their host. They secrete enzymes that break down organic structures.
Ex. Mycobacterium tuberculosis
Bacteria can cause disease by releasing toxins, which damage their host.
Ex. Stapylococcus aureus
Biowarfare is the deliberate exposure of people to biological toxins or pathogens such as bacteria or viruses.

21. Section 2
Bacteria
Antibiotics
Bacterial disease can be fought with soap, chemicals, and antibiotics.
Mutations that confer resistance to antibiotics are strongly favored in bacterial populations being treated with an antibiotic.

23. Bacteria Importance of Bacteria
Section 2
Bacteria
Importance of Bacteria
Bacteria are used to make foods, antibiotics, and other useful chemicals.
Mining companies use bacteria to concentrate desired elements from low-grade ore. Bacteria are also used to clean the environment and cycle important chemicals in the environment.