Session 6 - Metabolism & Genetics

• Metabolism is the series of biochemical reactions by which the cell breaks down or synthesizes various metabolites.
• Cells are primarily composed of elements: Carbon, Hydrogen, Oxygen, Nitrogen, Phosphorus, and Sulfur. These chemical elements are predominant in the cell..
• • Carbon is needed in the largest amount amounting to 50% of a cell’s dry weight.
  • Oxygen and hydrogen cover 25% of a cell’s dry weight when combined.
  • Nitrogen occupies 13% of the cell’s dry weight.
  • Phosphorus, Sodium, Potassium, Magnesium, and Selenium make up 5% of a cell’s dry weight when combined.
• Macronutrients


  are required in large amounts.
• Micronutrients


  are required in minute amounts.
• Examples of Micronutrients:

  • Trace elements as co-factor of certain enzymes
  • Vitamins as growth factors (organic micronutrient)
  • Iron (Fe) plays a major role in cellular respiration
• 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 (3) classes of transport systems:

  • simple transport
  • group translocation
  • ABC transport systems
• Simple Transport


  Major transport systems comprising of reactions that are driven by the energy inherent in the proton motive force.
• Simple major transports include two (2) reactions:

  1. Symport Reactions
  2. Antiport Reactions
• Symport reactions


  where a solute and a proton are cotransported in one direction.
• antiport reactions


  where a solute and a proton are transported in opposite directions.
• Group Translocation

  • The transported substance is chemically modified during the transport process.
  • An energy-rich organic compound (rather than the proton motive force) drives the transport event
• Microbes can be metabolically classified according to their carbon and energy source.
• All microbes 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.
• Most chemolithotrophs and phototrophs are autotrophs. 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).
• Redox reactions


  Also known as oxidation-reduction reactions; these require electron donors and electron acceptors.
• The substance oxidized (H2 ) as the electron donor, and the substance reduced (O2) as the electron acceptor.
• ATP


  The prime energy carrier in the cell. It consists of the ribonucleoside adenosine to which three phosphate molecules are bonded in series.
• Two (2) categories of metabolism:

  • anabolism
  • catabolism
• Anabolism


  -any process that results in synthesis of cell molecules and structures.
• Catabolism


  -breaks the bonds of larger molecules into smaller molecules.
• The Embden-Meyerhof-Parnas pathway or glycolysis is the universal pathway for the catabolism of glucose.
• 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.
• The pathway releases a small amount of ATP (2–3/glucose) and large amounts of fermentation products. Besides glucose, the fermentation of other sugars, amino acids, nucleotides and polymeric compounds is possible.
• 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 twocarbon electron donors, such as acetate.
• Electron transport chains


  Composed of membrane associated redox proteins that are arranged in order of their increasing E0’ values.
• Electron transport chains function in a concerted fashion to carry electrons from the primary electron donor to the terminal electron acceptor, which is O2 in aerobic respiration.
• Biosynthesis:

  1. Polysaccharides are important structural components of cells and are biosynthesized from activated forms of their monomers.
  2. Gluconeogenesis is the production of glucose from non-sugar precursors.
  3. Nucleotides are biosynthesized using carbon skeletons from several different sources
• Biosyntheses or anabolic reactions involve the assembly of smaller molecules into larger molecules, requiring the formation of bonds. Once formed, the bonds represent stored energy.
• Amino acids are formed from carbon skeletons to which ammonia is added from glutamate, glutamine, or a few other amino acids.