BIOB 170 N 1st Edition Lecture 3 Prokaryotes Prokaryotes are the earliest of life forms that appeared around 3.5 billion years ago.Their phylogenetics is unclear particularly at the phylum and class levels. Standardphylogenetics concepts may not apply to prokaryotes because of “horizontal gene flow.” Domain: Archaea Archaea were initially thought to be the most archaic of prokaryotes. They exhibit features of both bacteria and eukaryotes. General Characteristics Archaea are generally considered thermophiles (90-113oC) and halophiles. Habitats that include these organisms are hot springs with very low pH. However, they can be found in many other extreme environments. Many are methanogens found in anaerobic aquatic sediments. There are three distinctive Archaean traits. They lack peptidoglycan in the cell wall. Some have histones. Others are not sensitive to antibiotics. Domain: Bacteria Bacteria are the most widespread forms of life on earth. They fit in numerous ecological niches and have great metabolic diversity. Distinguishing features Many bacteria have a flagella, cell walls/extra-cellular features, genome organization, reproduction, and metabolic diversity. - Bacterial flagella are fundamentally different from eukaryotes. Eukaryotic flagella (undulipodium) consist of distinctive protein microtubule array (axoneme).These flagella are membrane-bound and rooted to the cytoplasm. These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.- Bacterial flagella consist of stiff tubular protein (filament). These flagella are not membrane-bound. Supports intelligent design. Bacterial metabolic diversity Autotrophic organisms make organic compounds (food). Examples of this are cyanophytes and purple-sulfur bacteria. There are two types of autotrophy – photosynthetic and chemosynthetic. - Photosynthetic organisms use light sources to make energy. It can be oxygenic ornon-oxygenic. Examples of organisms that use oxygenic photosynthesis are the cyanobacteria. Examples of organisms that use non-oxygenic photosynthesis are purple-sulfur bacteria. - Chemosynthetic organisms use organic or inorganic resources to make energy. Chemical energy is released by oxidation of the compounds. Oxidation is the removal of electrons and H from molecules to release energy. It yields energy to drive glucose formation. Heterotrophic organisms require pre-made organic compounds. There are two types of heterotrophy – photoheterotrophic and chemoheterotrophic.Photoheterotrophic organisms utilize photosynthesis, but require an organic carbon source. An example is the purple non-sulfur bacteria. - Chemoheterotrophic organisms require organic resources for energy and carbonsource. There are many examples of this system (numerous parasites, mutualistic bacteria, animals, etc.). All organisms require nitrogen. Amino acids, proteins, DNA, and RNA all contain anabundance of nitrogen. The primary reservoir of nitrogen is in the atmosphere as N2. This nitrogen is inert, meaning it is biologically unavailable.Nitrogen fixation Nitrogen fixation is the chemical conversion of N2 to NH4. Other than bacterial nitrogen fixation, there are three major sources of chemicallyaltered nitrogen – industrial (chemical) fixation, lightning discharge, and volcanic eruptions. All three require large amounts of energy. - We can take N2 and turn it into ammonia. It is very energetically costly. - Lots of energy and pressure is generated, and fixed nitrogen falls to the earth as fertilizer for plants. Nitrogenase is the enzyme used to catalyze the reaction and is inactivated by free O2. Thus, nitrogen fixation requires a hypoxic or anoxic environment. These conditions and the requirement of large amounts of energy constrain nitrogen fixation. There are two groups of bacteria that can fix nitrogen – cyanophytes and Rhizobia.- Cyanophytes are free-living or mutualistic, oxygen producing, photosynthetic organisms. Nitrogen fixation occurs in the heterocysts of the organisms. - Rhizobia are mutualistic symbionts and heterotrophic organisms. Legumes are well known for their symbiotic relationship with Rhizobium. Leg hemoglobin is utilized for this process. Nitrogen cycle: a biogeochemical cycle Numerous chemical transformations of a given element are involved in the nitrogen cycle. Through living and nonliving reservoirs, elements move through the cycle.The fundamental steps of the nitrogen cycle are mediated by various bacteria. There are metabolically diverse assemblages – photoautotrophic, chemoheterotrophic, chemosynthetic, and