Chapter 19 Bacteria & Viruses

Bacteria Microscopic life covers nearly every square centimeter of Earth. Prokaryotes are most common microorganism - singled celled and lack a nucleus - cell walls of peptidoglycan or lipopolysaccharides - various shapes and sizes a. bacilli – rod shaped b. cocci – spherical shaped c. spirilla – twisting spiral

Bacteria Differences in cell wall composition can be detected through Gram stain *presence of peptidoglycan will give a purple stain or gram positive *less peptidoglycan, more complex structure with lipopolysaccharide outer layer, will give a pink stain or gram negative Locomotion or movement is another feature that can separate different types of bacteria - presence or absence of flagella

Bacteria Metabolism modes 1. Chemoheterotrophs – consume organic molecules for energy (carbon) 2. Photoheterotrophs – produce food from sunlight, but also consume organic molecules for energy (carbon) 3. Photoautotrophs – produce all sources of food and energy 4. Chemoautotrophs – produce all food and energy sources from organic molecules

Energy Release Bacteria need a constant supply of energy for life processes and in order to carry out respiration or fermentation or both. - obligate aerobes – require oxygen - obligate anaerobes – must live without oxygen - facultative anaerobes – can survive with or without oxygen

Reproduction When conditions are favorable bacterial growth can be exponential in a short time - binary fission – replication of DNA and dividing or separate to produce new organism *form of asexual reproduction - conjugation – exchange of genetic information between two bacterium in which a mating bridge connects them

Importance of Bacteria Bacteria are vital to the living world in 3 ways: 1. Some are producers 2. Some are decomposers - nitrogen fixers – convert N2 into usable form for plants and organisms to use 3. Human symbiotic relationship Ex: E. coli in the small intestine

Viruses Viruses are smaller and more simple than prokaryotes Lack structures and metabolic machinery found in most cells – not living Most are a nucleic acid enclosed in a protein coat called a capsid Genomes have many possibilities -double stranded DNA -single stranded DNA -double stranded RNA -single stranded RNA

Common Virus Structures

Viruses Isolated virus cannot produce or survive long without a host cell Each virus has a host range of cells it can infect -lock and key fit occurs between outside of virus and specific receptor molecules on the surface of the cell -some have wide range, Ex: West Nile -target specific tissues – Ex: cold virus in upper respiratory tract

Viral Infection & Replication 1. Virus enters cell and uncoats, releasing viral DNA and capsid proteins 2. Host enzymes replicate the viral genome 3. Host enzymes transcribe viral genome to make mRNA then translate to make viral proteins 4. Viral genomes and capsids self assemble into new virus particles and exit cell

Lytic Cycle Lytic cycle – reproductive cycle that results in death of host cell -refers to last stage in which bacterium lyses and releases phages produced

Lysogenic Cycle Lysogenic cycle – replication of phage genome without destroying host -viral DNA is incorporated by genetic recombination into specific site in host’s chromosome – creates a prophage -prophage remains silent but is passed each time the host cell divides and synthesizes its DNA *prophage can switch to lytic cycle and release from host -triggers include exposure to radiation or presence of certain chemicals

Lysogenic Cycle

Retroviruses Virus that contains RNA, upon infection replicates a copy of DNA to be incorporated into host genome -can be dormant for long periods of time -backward copying of genetic information Ex: Human Immunodeficiency Virus (HIV) which leads to AIDS

Viruses vs. Cells