1. Metabolism: Energy Release and Conservation
Chapter 9
Metabolism: Energy Release and Conservation

2. Sources of energy most microorganisms use one of three energy sources
the sun
reduced organic compounds
reduced inorganic compounds
the chemical energy obtained can be used to do work
Figure 9.1

3. Chemoorganotrophic fueling processess
Figure 9.2

4. Chemoorganic fueling processes-respiration
Most respiration involves use of an electron transport chain
aerobic respiration: final electron acceptor is oxygen
anaerobic respiration
final electron acceptor is different exogenous NO3-, SO42-, CO2, Fe3+ or SeO42-.
organic acceptors may also be used
As electrons pass through the electron transport chain to the final electron acceptor, a proton motive force (PMF) is generated and used to synthesize ATP

5. Chemoorganic fueling processes - fermentation
Uses an endogenous electron acceptor
usually an intermediate of the pathway e.g., pyruvate
Does not involve the use of an electron transport chain nor the generation of a proton motive force
ATP synthesized only by substrate-level phosphorylation

6. Aerobic catabolism-An Overview
Three-stage process
large molecules (polymers)  small molecules (monomers)
oxidation of monomers to pyruvate
oxidation of pyruvate by the tricarboxylic acid cycle (TCA cycle)

7. many
different
substrtaes
are
funneled
into
the TCA cycle
ATP made
primarily by
oxidative
phosphory-
lation
Figure 9.3

8. Amphibolic Pathways Function both as catabolic and anabolic pathways
Examples:
Embden-Meyerhof pathway
pentose phosphate pathway
tricarboxylic acid (TCA) cycle
Figure 9.4

9. The Breakdown of Glucose to Pyruvate
Three common routes
Embden-Meyerhof pathway
pentose phosphate pathway
Entner-Doudoroff pathway

10. The Embden-Meyerhof Pathway (glycolysis)
Occurs in cytoplasmic matrix
Oxidation of glucose to pyruvate can be divided in two stages
-glucose to fructose 1,6 -bisphosphate (6 carbon)
-fructose 1, 6-bisphosphate to pyruvate (two 3 carbon)

11. Glycolysis oxidation step – generates NADH ATP by substrate-level
phosphorylation
Figure 9.5

12. Summary of glycolysis
glucose 
2 pyruvate
2ATP
2NADH + 2H+

13. The Pentose Phosphate Pathway
Can operate at same time as glycolytic pathway
Operates aerobically or anaerobically an
Amphibolic pathway

14. produce
NADPH
no ATP
important
intermediates
Figure 9.6

15. sugar transformation reactions
Figure 9.7

16. Summary of pentose phosphate pathway
glucose-6-P 
6CO2
12NADPH
Glycolytic intermediates

17. The Entner-Doudoroff Pathway
reactions of
pentose
phosphate
pathway
yield per glucose molecule:
1 ATP
1 NADPH
1 NADH
reactions of
glycolytic
pathway
Figure 9.8

18. The Tricarboxylic Acid Cycle
Also called citric acid cycle and Kreb’s cycle
Common in aerobic bacteria
Anaerobes contain incomplete TCA cycle
An Amphibolic pathway

19. Figure 9.9

20. Summary For each acetyl-CoA molecule oxidized, TCA cycle generates:
2 molecules of CO2
3 molecules of NADH
one FADH2
one GTP

21. Electron Transport and Oxidative Phosphorylation
Only 4 ATPs are synthesized directly from oxidation of glucose to CO2 (by substrate-level phosphorylation)
Most ATP made when NADH and FADH2 are oxidized in electron transport chain (ETC)

22. The Electron Transport Chain
Series of electron carriers transfer electrons from NADH and FADH2 to a terminal electron acceptor
Electrons flow from carriers with more negative E0 to carriers with more positive E0

23. Electron transport chain…
As electrons transferred, energy released
In bacteria and archaea electron carriers are in located plasma membrane
In eucaryotes the electron carriers are within the inner mitochrondrial membrane

24. large difference in E0 of NADH and E0 of O2 large amount of
energy released
Mitochondrial electron transport chain. Electron carriers are organized into 4 complexes that are linked by CoQ and Cyt c.
Figure 9.10

25. Mitochondrial ETC electron transfer accompanied by
Proton release into the intermembrane space occurs when electrons are transferred from carriers (e.g., FMN and A) that carry both electrons and protons to components (e.g., FES proteins and Cyt) that transport only electrons.
electron transfer accompanied by
proton movement across inner
mitochondrial membrane
Figure 9.11

26. Electron Transport Chain of E. coli
branched pathway
upper branch –
stationary phase and
low aeration
lower branch – log
phase and high
aeration
Figure 9.12

27. Oxidative Phosphorylation
Process by which ATP is synthesized as the result of electron transport driven by the oxidation of a chemical energy source

28. Proton Motive Force
Is the most widely accepted hypothesis to explain oxidative phosphorylation
electron carriers are organized in the membrane such that protons move outside the membrane as electrons are transported down the chain
proton expulsion results in the formation of a concentration gradient of protons and a charge gradient
The combined chemical and electrical gradient (electro chemical ) across the membrane is the proton motive force (PMF)

29. Chemiosmosis
Peter Mitchell in 1961 proposed that the electrochemical gradient (proton and pH) across a membrane is responsible for the ATP synthesis. He likened this process to osmosis, the diffusion of water across a membrane, which is why it is called chemiosmosis.
Peter Mitchell received the Nobel Prize in 1978 for this concept.

30. PMF drives ATP synthesis(Chemiosmosis)
Diffusion of protons back across membrane (down gradient) drives formation of ATP
ATP synthase
enzyme that uses PMF down gradient to catalyze ATP synthesis

31. ATP Synthase Figure 9.14 (a)
The major structural features of ATP synthase deduced from X-ray crystallography and other studies. F1 is a spherical structure composed largely of alternating  and  subunits; the three active sites are on the  subunits. The  subunit extends upward through the center of the sphere and can rotate. The stalk ( and  subunits) connects the sphere to F0, the membrane embedded complex that serves as a proton channel. F0 contains one a subunit, two b subunits, and 9-12 c subunits. The stator arm is composed of subunit a, two b subunits, and the  subunit; it is embedded in the membrane and attached to F1. A ring of c subunits in F0 is connected to the stalk and may act as a rotor and move past the a subunit of the stator. As the c subunit ring turns, it rotates the shaft ( subunits).
Figure 9.14 (a)

32. The binding change mechanism of ATP synthesis is depicted
The binding change mechanism of ATP synthesis is depicted. The F1 sphere is viewed from the membrane side. The 3 active sites appear able to exist in 3 different conformations: an inactive open (O) conformation with low affinity for substrates, an inactive (L) conformation with fairly loose affinity for the substrates, and an active tight (T) conformation that has high affinity for substrates. In the first step, ADP and Pi bind to the O site. Then the  subunit rotates 120° with the input of energy, presumably from proton flow through F0. This rotation causes conformation changes in all three subunits resulting in a release of newly formed ATP and a conversion of the L site to an active T conformation. Finally, ATP is formed at the new T site while more ADP and Pi bind to the unoccupied O site and everything is ready for another energy-driven  subunit rotation.
Figure 9.14 (b)

33. Inhibitors of ATP synthesis
Blockers
inhibit flow of electrons through ETC
Uncouplers
allow electron flow, but disconnect it from oxidative phosphorylation
many allow movement of ions, including protons, across membrane without activating ATP synthase
destroys pH and ion gradients
some may bind ATP synthase and inhibit its activity directly

34. Maximum Theoretic ATP Yield from Aerobic Respiration
Figure 9.15

35. Theoretical vs. Actual Yield of ATP
Amount of ATP produced during aerobic and anaerobic respiration varies depending on growth conditions and nature of ETC
Comparatively, anaerobic respiration yields fewer ATP that aerobic respiration
In fermentation yileds very few ATP