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Prokaryotes Prokaryotes • Classification of prokaryotes has dramatically changed due to analysis of the genomes of various types of cells: • The description of these organisms as members of Kingdom Monera, has been abandoned and replaced with a three domain system. These Domains are as follows: – Domain Bacteria – Domain Archaea – Domain Eukarya • The domains bacteria and archaea contain the prokaryotic organisms. • Domain Eukarya include the protists and the other multicellular kingdoms. General Bacterial Structure General Characteristics •Bacteria are the smallest "living" organisms •Are prokaryotic cells •Lack Nucleus •DNA is naked. - a single loop - not bound into a chromosome. •May contain plasmids (small circular fragments of DNA) •Lack membrane-bound organelles •Usually have an outer Cell Wall. •Sometimes have an Outer Capsule - These stain red in a Gram Stain test and are called Gram Negative bacteria. •Those without an outer capsule stain blue in the gram stain test and are called Gram Positive Bacteria BACTERIAL CLASSIFICATION: • Bacteria are classified generally by 3 characteristics – The bacterial cell shape – The bacterial cell arrangements – Ability to accept a Gram stain Bacterial Shape: • Bacteria have 4 basic shapes: – Spherical - cocci – Rod-shaped – bacilli – Bent rod shaped - Vibrios – Spiral – spirilli Bacterial Arrangement: • Bacteria have 3 basic arrangements: – Occurring singly = “Mono” arrangement – Occurring in pairs = “Diplo” arrangement – Occurring in long chains = “Strepto” arrangement – Occurring in clusters = “Staphlo” arrangement Gram Staining: • Bacteria can be categorized by their ability to accept a gram stain. – Bacteria are exposed to several staining agents; Crystal Violet, Gram’s Iodine, and safranine. Gram Negative Bacteria • If the bacteria possesses a cell capsule, it will retain a pink color. This is referred as to a “Gram Negative” bacteria • If the bacteria lacks a cell capsule it will retain a blue color. This is referred to as a “Gram Positive” bacteria Gram Positive Bacteria How Bacteria obtain energy: • Two major categories: – Autotrophs - Make their own energy - 2 types • Phototrophic autotrophs - Get energy from sunlight • Chemotrophic autotrophs - Get energy from inorganic molecules (eg. Sulfides) – Heterotrophs - Energy obtained from other organisms • Chemotrophic heterotrophs - obtain energy by dissolving/absorbing organic material • Phototrophic heterotrophs - meet some energy needs from photosynthesis, but must absorb organic compounds. Bacterial Respiration 3 major categories • Obligate aerobes. - Must have O2 in order to live • Obligate anaerobes - Must live in an O2 free environment • Facultative anaerobes - Can live with or without O2. Bacterial Reproduction: • Bacteria reproduce through binary fission. • Can engage in primitive sexual reproduction called conjugation. – A bridge is formed between 2 bacteria – Plasmids are shared across bridge, thus exchanging genetic information. – In times of harsh conditions, bacteria can form endospores, to encapsulate themselves in a dormant state, until conditions improve. Motility • Some bacteria are motile - can move by either thrashing, secreting lubricating secretions or through use of a flagellum Archaea Evolutionary Relationships • Analysis of molecules found within the cells suggests that eukaryotes are more closely related to archaea than to bacteria. Major Groups of Archaea • Three major groups of archaea are found in extreme habitats. – Methanogens are found in anaerobic environments.such as marshes and in the intestinal tracts of animals. They produce methane as a result of cellular respiration. – Halophiles are found in environments with high salt concentration such as the great salt lake or soil with a high salt concentration. – Thermoacidophiles live in hot, acidic environments such as hot springs and hydrothermal vents.
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