Chapter 19 Biology – Miller • Levine 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

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”)

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.

Lytic Infection

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.

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… 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

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

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

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 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

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