MODULE 5

• Microbial Nutrients - Cell are primarily composed of elements C, H, O, N, P, and S. All microbes require a core set of nutrients.
• These chemical elements are predominant in the cell:

  • C is needed in the largest amount (50% of a cell’s dry weight)
  • O and H are next (combined, 25% of dry weight)
  • N follows (13%)
  • P, S, K, Mg, and Se combine for less than 5% of a cell’s dry weight
• Macronutrients are required in large amounts.
• Micronutrients are required in minute amounts.
• The active transport of nutrients into the cell is an energy requiring process driven by ATP (or some other energy-rich compound) or by the proton motive force.
• Three classes of transport systems: simple, group translocation, and ABC systems.

  Each functions to accumulate solutes against the concentration gradient.
• Simple transport reactions are driven by the energy inherent in the proton motive force
• Major Transport

  symport reactions - where a solute and a proton are cotransported in one direction.
• Major Transport

  antiport reactions - where a solute and a proton are transported in opposite directions.
• Group translocation differs from simple transport in two important ways:

  (1) the transported substance is chemically modified during the transport process, and

  (2) an energy-rich organic compound (rather than the proton motive force) drives the transport event.
• ABC Transport System

  “ABC” stands for ATP - binding cassette - a structural feature of proteins that bind ATP.
• ABC Transport System - transport systems that employ a periplasmic binding protein along with transmembrane and ATP-hydrolyzing components
• Catabolism - energy-yielding reactions
• All microorganisms conserve energy from either the oxidation of chemicals or from light.
• Chemotrophs - organisms that conserve energy from chemicals
• Chemoorganotrophs use organic chemicals as their electron donors, while chemolithotrophs use inorganic chemicals.
• Phototrophic organisms convert light energy into chemical energy (ATP) and include both oxygenic and anoxygenic species.
• Heterotroph, its cell carbon is obtained from one or another organic compound.
• An autotroph, by contrast, uses carbon dioxide (CO2) as its carbon source.
• Autotrophs are also called primary producers because they synthesize new organic matter from inorganic carbon (CO2).
• Calvin cycle is the major biochemical pathway by which phototrophic organisms incorporate CO2 into cell material.
• Enzymes are protein catalysts that increase the rate of biochemical reactions by activating the substrates that bind to their active site.
• Enzymes are highly specific in the reactions they catalyze, and this specificity resides in the three-dimensional structures of the polypeptide(s) that make up the protein(s).
• Chemical reactions in the cell are accompanied by changes in energy, expressed in kilojoules. Reactions either release or consume free energy.
• ∆G0 is a measure of the energy released or consumed in a reaction under standard conditions and reveals which reactions can be used by an organism to conserve energy
• Oxidation–reduction reactions require electron donors and electron acceptors. The tendency of a compound to accept or release electrons is expressed by its reduction potential (E0’).
• The substance oxidized (H2) as the electron donor, and the substance reduced (O2) as the electron acceptor.
• Redox reactions in a cell often employ redox coenzymes such as NAD+/NADH as electron shuttles.
• The energy released in redox reactions is conserved in compounds that contain energy-rich phosphate or sulfur bonds.
• ATP - the prime energy carrier in the cell. Consists of the ribonucleoside adenosine to which three phosphate molecules are bonded in series.
• universal pathway for the catabolism of glucose is the Embden– Meyerhof–Parnas pathway, better known as glycolysis.
• The glycolytic pathway is used to break down glucose to pyruvate and is a widespread mechanism for energy conservation by fermentative anaerobes that employ substrate-level phosphorylation.
• Respiration offers an energy yield much greater than that of fermentation.
• The citric acid cycle generates CO2 and electrons for the electron transport chain. The pathway by which pyruvate is oxidized to CO2.
• The glyoxylate cycle is necessary for the catabolism of two-carbon electron donors, such as acetate.
• Electron transport chains are composed of membrane associated redox proteins that are arranged in order of their increasing E0’ values.
• The electron transport chain functions in a concerted fashion to carry electrons from the primary electron donor to the terminal electron acceptor, which is O2 in aerobic respiration.
• Polysaccharides are important structural components of cells and are biosynthesized from activated forms of their monomers.
• Gluconeogenesis is the production of glucose from non-sugar precursors.
• Amino acids are formed from carbon skeletons to which ammonia is added from glutamate, glutamine, or a few other amino acids.