Bacterial Physiology (Micr430)

Lecture 3Energy 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

Produceenergy

Utilizeenergy

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.

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 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 membraneH+ p = -------- = Ψ - 60pH 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 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

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