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Bacterial Physiology (Micr430). Lecture 3 Energy Production and Metabolite Transport (Text Chapters: 4, 16). Metabolism. Definition: metabolism – total of all chemical reactions occurring in a cell. Bacterial metabolism. Large & more complex molecules. Produce energy.
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Bacterial Physiology (Micr430) Lecture 3 Energy Production and Metabolite Transport (Text Chapters: 4, 16)
Metabolism • Definition: metabolism – total of all chemical reactions occurring in a cell Bacterial metabolism Large & more complex molecules Produce energy Utilize energy Catabolism Anabolism Small & simpler molecules
ENERGY PRODUCTION • Substrate-level phosphorylation • Oxidative phosphorylation
Catabolism • Three stages of catabolism • Large nutrient molecules (e.g., glycan) are broken down to the constituent parts (monomers). (not much energy released) • Monomers degraded into a few simpler molecules. -> substrate-level phosphorylation • These simpler molecules enters TCA cycle to generate CO2 and a lot of ATP, NADH and FADH2. -> oxidative phosphorylation
Catabolism: class question • Name 3 kinds of large nutrient molecules (macromolecules): 1. 2. 3.
Stages 2 and 3 Fig 8.1
Oxidative Phosphorylation • When a carbohydrate is oxidized via a respiratory mechanism, energy is generated by passing electrons through a series of electron acceptors and donors until they ultimately reach a final e- acceptor such as O2 or nitrate • Energy inherent in carbohydrate is gradually released during this series of coupled oxidation-reduction reactions and used to pump protons out of the cell via the membrane-bound cytochrome systems.
Oxidative Phosphorylation • Since membranes are impermeable to protons, transfer of protons (outward) establishes an electrochemical gradient or proton motive force (PMF) across the cell membrane DmH+ Dp = -------- = DΨ - 60DpH F Where: DΨrepresents the transmembrane electrical potential DpH is the pH difference across the membrane
Electron Transport System • Cytoplasmic membranes of bacteria contain electron transport system (ETS) that generate PMF by coupling oxidation of NADH and other substrates to expulsion of protons. • ETS consists of cytochromes, iron-sulfur cluster enzymes, flavoproteins (containing FMN) and quinolones
Electron Carriers Fig 4.3 Fig 4.2 Fig 4.4
Electron Carriers Fig 4.5
Proton Translocations Fig 4.11
PMF to Energy • The cell can directly generate ATP from PMF by reversing the action of the major H+-translocating ATPase. These are called F1F0-type ATPase due to two structurally and functionally distinct entities (F1F0) • PMF can also be used to drive the transport of some metabolites into the cell. • Flagellar motor is driven by PMF; each flagellar rotation requires the influx of 256 H+
F1 F0
METABOLITE TRANSPORT • Cell membrane serves as a permeability barrier – hydrophobic lipid bilayers maintain cell’s internal environment from outside. • Everything that is not lipid-soluble enters and leaves cell through integral membrane transporters (or carriers)
Energy dependent transport • When transporting a solute against its concentration gradient, the process needs energy (light, chemical or electrochemical). • Bacterial transport systems: • Primary, driven by an energy-producing metabolic event • Secondary, driven by electrochemical gradients
Examples of secondary transport • A & B, symport • C, antiport • D, uniport Fig 16.4
Primary transports driven by ATP • H+ transport (ATP synthase) • K+ transport in E. coli • Transport systems in Gram- bacteria use periplasmic proteins
Phosphotransferase System • Phosphotransferase system (PTS) is involved in both the transport and phosphorylation of a large number of carbohydrates, in movement toward these carbon sources and in regulation of several other metabolic pathways • In this group translocation transport system, carbohydrate phosphorylation is coupled to carbohydrate transport • The energy for these transport systems is provided by the EMP intermediate phosphoenolpyruvate (PEP)
