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 structures 2. They do not carry out functions of respiration, growth or development 3. Must have host cell to replicate 4. Do not metabolize, no energy 5. They are parasitic Named after the disease they caused Bacteriaphage – virus that infects a bacterium like E.coli

Viral structure: 1. Inner core of genetic material either RNA or DNA 2. Capsid – or outer coat of protein Attachment 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 host The 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

Viruses Provirus – 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, shingles Retrovirus – RNA virus that through reverse transcriptase produces DNA HIV, cancers, tumor viruses,papilloma virus What fights them: 1.White Blood Cells-engulf virus and ingests them 2.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 O 2 Anaerobic environment that produces methane gas they live in marshes, lakes, sediments and digestive tracts of cows, sewage disposal plants High salt water concentrations like the Great Salt lake and Dead Sea Hot acidic water of sulfur springs, cracks deep in the Pacific Ocean, autotrophic producer for food chain

2. Eubacteria – heterotrophs, most commonly known as germs, live almost everywhere and use organic molecules as a food source Phyla: 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 bacteria this 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. Bacteria in Yogurt Staphylococci Infection

Structure of Bacteria Cell 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 Bacteria 1. Shape: Cocci - round bacterial cells. Bacilli - rod-shaped bacterial cells. Spirilli - spiral-shaped bacterial cells. 2. Clustering staphylo - a prefix used with the shape name to indicate clusters.clusters. strepto - a prefix used with the shape name to indicate filamentsfilaments

Respiration: Obligate anaerobes - cannot survive in the presence of atmospheric oxygen. Ex: TB Facultative anaerobes - can live with or without atmospheric oxygen. Use fermentation Obligate aerobes - cannot survive without atmospheric oxygen. Ex: syphilis Two types of cell walls in Eubacteria: hypotonic environment – higher concentration outside cell 1. 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 pressure Reproduction: Asexual, by binary fission - the DNA replicates and then the cell pinches inward and splits in two Conjugation - 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 Bacteria Nitrogen fixation – conversion of nitrogen gas N 2 into ammonia NH 3 which other bacteria then convert to nitrite and nitrate which plants than use and we can utilize the nitrogen into DNA, RNA and ATP