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 Catabolism Anabolism Large & more complex molecules Small & simpler molecules Produce energy Utilize energy

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 CO 2 and a lot of ATP, NADH and FADH 2. -> oxidative phosphorylation

Catabolism: class question Name 3 kinds of large nutrient molecules (macromolecules):

Fig 8.1 Stages 2 and 3

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 O 2 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  H +  p = =  Ψ - 60  pH F Where:  Ψ represents the transmembrane electrical potential  pH 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 4.2 Fig 4.4 Fig 4.3

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 F 1 F 0 - type ATPase due to two structurally and functionally distinct entities (F 1 F 0 ) 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 +

F1F1 F0F0

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

Fig16.6

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)

Fig16.9