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

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. 2

Viruses Is a Virus Alive? Section 1 Viruses Is a Virus Alive? Discovery of Viruses Viruses do not have all the characteristics of life and are therefore not considered to be alive. 3

Viruses Viral Structure Section 1 Viruses Viral Structure Characteristics of Viruses Viruses consist of segments of a nucleic acid (DNA or RNA) contained in a protein coat, and some have an envelope. 4

Viruses Viral Reproduction Section 1 Viruses Viral Reproduction Viral Replication 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. 5

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. 6

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. 7

Viruses Viral Diseases Section 1 Viruses Viral Diseases Emerging Viruses Emerging viruses are geographically isolated viruses that cause disease in humans. Prions and Viroids Viroids are infectious RNA molecules that cause disease in plants, and prions are infectious proteins that cause disease in certain animals. 8

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. 9

Bacteria Bacterial Structure Section 2 Bacteria Bacterial Structure Characteristics of Bacteria Bacteria differ from eukaryotes in their cellular organization, cell structures, and metabolic diversity. Bacteria are grouped according to their ribosomal RNA sequences and the way they obtain energy. Bacterial Cell Shapes A bacteria is one of three shapes: rod-shaped (bacillus), round-shaped (coccus), and spiral-shaped (spirillum). 10

Bacteria Bacterial Structure continued Section 2 Bacteria Bacterial Structure continued Gram Staining Bacteria can be classified according to their cell wall structure. Gram staining can be used to distinguish these two groups. 11

Bacteria Obtaining Energy Section 2 Bacteria Obtaining Energy Photosynthesizers Photosynthetic bacteria can be classified into four major groups: purple nonsulfur bacteria, green sulfur bacteria, purple sulfur bacteria, and cyanobacteria. Chemoautotrophs Chemoautotrophs obtain energy by removing electrons from inorganic molecules such as ammonia, hydrogen sulfide, or methane. Heterotrophs Most bacteria are heterotrophs and many are aerobic. 12

Bacteria Pathogenic Bacteria Section 2 Bacteria Pathogenic Bacteria Bacteria Can Metabolize Their Host Bacteria can cause disease by metabolizing nutrients in their host. Bacterial Toxins Bacteria can cause disease by releasing toxins, which damage their host. Biowarfare Biowarfare is the deliberate exposure of people to biological toxins or pathogens such as bacteria or viruses. 13

Section 2 Bacteria Antibiotics Fighting Bacteria Bacterial disease can be fought with soap, chemicals, and antibiotics. Antibiotic-Resistant Bacteria Mutations that confer resistance to antibiotics are strongly favored in bacterial populations being treated with an antibiotic. 14

Bacteria Importance of Bacteria Section 2 Bacteria Importance of Bacteria Food and Chemical Production Bacteria are used to make foods, antibiotics, and other useful chemicals. Mining and Environmental Uses of Bacteria 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. 15