Viruses and Bacteria

Chapter 18

Viruses–small ½-1/100 size of bacterium 20

nm - Considered non–living because:1. They are not cells with cell structures2. They do not carry out functions of respiration, growth or development3. Must have host cell to replicate4. Do not metabolize, no energy5. They are parasitic

Named after the disease they causedBacteriaphage – virus that infects a bacterium like E.coli

Viral structure:1. Inner core of genetic material either RNA or DNA2. Capsid – or outer coat of proteinAttachment specific to receptor proteins

2 types of Viral Replication:1. Lytic Cycle – virus reproduces with

host cell than bursts from it killing it

1. Attachment: Virus attaches itself to the cell.

2. Entry: Enzymes weaken the cell wall and nucleic acid is injected into the cell, leaving the empty capsid outside the cell. Many viruses actually enter the host cell intact.

3. Replication: Viral DNA takes control of cell activity.

4. Assembly: All metabolic activity of the cell is directed to assemble new viruses.

5. Release: Enzymes disintegrate the cell in a process called lysis, releasing the new viruses

2. Lysogenic Cycle – replication cycle that integrates virus’s nucleic acid into chromosome

of hostThe virus attaches itself and injects its DNA into the cell. The viral DNA attaches itself to the host DNA, becoming a new set of cell genes called a prophage. When the host cell divides, this new gene is replicated and passed to new cells. This causes no harm to the cell, but may alter its traits. Now there are two possibilities: The prophage survives as a permanent part of the DNA of the host organism. Some external stimuli can cause the prophage to become active, using the cell to produce new viruses

VirusesProvirus – the viral DNA is integrated into the host’s genetic material, continues to replicate and may become active at any time

Cold sores, Hepatitis B, chicken pox, shinglesRetrovirus – RNA virus that through reverse transcriptase produces DNAHIV, cancers, tumor viruses ,papilloma virus

What fights them:1.White Blood Cells-engulf virus and ingests them2.Interferons – protein that interferes with ability

of the virus to penetrate host cell Origination of viruses from host cells newer form of life

Prokaryotes – unicellular organisms without membrane bound organelles

2 Kingdoms:1. Arachaebacteria – extreme habitats, no O2

Anaerobic environment that produces methane gas they live in marshes, lakes, sediments and digestive tracts of cows, sewage disposal plantsHigh salt water concentrations like the Great Salt lake and Dead SeaHot acidic water of sulfur

springs, cracks deep in the Pacific Ocean, autotrophic producer for food chain www.physics.uc.edu

2. Eubacteria – heterotrophs, most commonly known as germs, live almost everywhere and use organic molecules as a food sourcePhyla:Cyanobacteria: these bacteria are photosynthetic, carrying on the same chemical processes as green plants. Spirochetes: gram-negative, spiral-shaped, heterotrophic bacteria that move with a corkscrew-like rotation. These bacteria live freely in the environment or have a symbiotic or parasitic relationship with other organisms.

Phyla (cont)

Proteobacteria: this group of gram-negative bacteria includes the human intestinal bacteria Escherichia coli, bacteria that extract energy from minerals, and nitrogen-fixing bacteria that convert atmospheric nitrogen into nitrates in the soil.

Gram-positive bacteriathis large group of bacteria includes the streptococci bacteria that cause strep throat, the lactic acid producing bacteria that turn milk into yogurt, the lactobacilli that cause tooth decay, and soil bacteria that produce many antibiotics.

www.carnegieinstitution.org Bacteria in Yogurt

StaphylococciInfection

Structure of BacteriaCell wall - some rigid and others flexible. Cell membrane - same as other cells. Cytoplasm - same as other cells. DNA - a single, circular chromosome located in the cytoplasm. Remember, bacteria cells do not have a nucleus. Capsule - a thick, gel-like, protective coating on some bacteria cells. Pili - short, hair like protein

structures on the surface of some bacteria that help them stick to host cells.

Flagella - long protein structures that turn to propel some bacteria cells.

Identifying Bacteria1. Shape:

Cocci - round bacterial cells. Bacilli - rod-shaped bacterial cells. Spirilli - spiral-shaped bacterial cells.

2. Clusteringstaphylo - a prefix used with the shape name to indicate clusters. strepto - a prefix used with the shape name to indicate filaments

Respiration:Obligate anaerobes - cannot survive in the presence of atmospheric oxygen. Ex: TBFacultative anaerobes - can live with or without atmospheric oxygen. Use fermentationObligate aerobes - cannot survive without atmospheric oxygen. Ex: syphilisTwo types of cell walls in Eubacteria: hypotonic environment – higher concentration outside cell1. Gram-positive bacteria - have a thick peptide layer, retain the crystal violet, and appear purple when viewed under a microscope. 2. Gram-negative bacteria - have a thin peptide layer, take up the pink stain, and appear pink when viewed under a microscope.

Sir Alexander Flemming 1928 – discovered penicillin because it destroyed the cell walls in the bacteria – bacteria bursts due to pressureReproduction: Asexual, by binary fission - the DNA replicates and then the cell pinches inward and splits in twoConjugation - two cells exchange a portion of their DNA material replaces old material in the cell. While this increases the genetic variability in the organisms, it is not true sexual reproduction. Endospores - during adverse conditions, the DNA is encased in a protective envelope. This endospore can lie dormant for years or until favorable conditions return. Tetanus, botulism

Importance of BacteriaNitrogen fixation – conversion of nitrogen gas N2 into ammonia NH3 which other bacteria then convert to nitrite and nitrate which plants than use and we can utilize the nitrogen into DNA, RNA and ATP