2 Kingdoms Archaebacteria and Eubacteria (P5).notebook 1 November 02, 2010 Characteristics THE LIFE OF A PROKARYOTE • Prokaryotes are single-celled organisms. They are the smallest, simplest organisms. • The group includes: o Archaebacteria are found in anaerobic and extreme conditions (high [salt], high temperature, and low pH), similar to what are believed to be the conditions on the early Earth. § Earth's early atmosphere did not contain oxygen, therefore the earliest organisms were anaerobic. o Eubacteria includes the traditional bacteria and is the larger of the two. • They are found in nearly every habitat studied, including some that no other organism is able to withstand. • Bacteria have a cell wall and cell membrane, but no membrane-bound organelles such as a nucleus, mitochondria, chloroplasts, Golgi apparatus, or ER. Some are covered by a layer of “slime” called a capsule. Early Atmosphere Primitive Earth Early Atmosphere of Primitive Earth • Probably H 2 and He -Possibly lost to space because Earth's gravity is not strong enough to hold lighter gases • Gases produced were probably similar to those created by modern volcanoes (H 2 O, CO 2 , SO 2 , CO, Cl 2 , N 2 , H 2 ) and NH 3 and CH 4 . -No free O 2 at this time (not found in volcanic gases). Back Shapes Cilia and Flagella • Some bacteria are able to move using special cell structures called cilia and flagella. o Hair-like cilia (singular, cilium) and tail-like flagella (singular, flagellum) are projections from the cell. o By repetitive beating (like a bending motion), they cause the cell to move. Think of oars in a boat. Flagella can propel the cell by waving back and forth. § If a cell is fixed in place, they can also cause water to move across the surface. . Resp/Nutr RESPIRATION • Obligate aerobes must have oxygen. • Obligate anaerobes can not survive in the presence of oxygen. • Facultative anaerobes will use oxygen if it is present but do not need it. NUTRITION • Most are heterotrophic… o Some are parasites which live off a living host. o Some are decomposers, feeding on dead organisms and waste. • Some are autotrophic… o Either use chemicals as a source of energy (chemoautotrophs) or are photosynthetic (photoautotrophs). Early symptomatic HIV infection: Mycobacterium marinum infection on the hand Bacterial Pericarditis Reproduction REPRODUCTION • Prokaryotes have a single circular chromosome attached to the inside of the plasma membrane. • Asexual reproduction o Prokaryotes reproduce by simply splitting in two in a process called binary fission. o The DNA is copied and the cell divides into two identical cells. • Sexual reproduction o Sexual reproduction combines genes from two different individuals and increases variation. Prokaryotes do not technically reproduce sexually but can mix genes with one another. o Conjugation - Two cells join briefly and one cell donates some DNA (called a plasmid) to the other one. Sometimes part of the cell‛s chromosome is donated as well. o Transformation - Bacteria can also pick up pieces of DNA from the environment. o Transduction - Sometimes viruses transfer pieces of DNA from one cell to another. • Endospores o Some bacteria form endospores when environmental conditions become unfavorable. o Endospores are DNA and a small amount of cytoplasm enclosed in a tough cell wall. They are resistant to extremes in temperature, drying, and harsh chemicals. • Mutation is a large source of genetic diversity in bacteria. Single Chromosome Conjugation Endospores Binary Fission