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Figure 6.00b. Figure 6.3. Unnumbered Figure 06_UN101a. Unnumbered Figure 06_UN92b. Unnumbered Figure 06_UN101c.
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Hydrogens and high energy electrons stripped off of organic molecules are used to power an electron transport system that generates an H+ gradient that in turn powers the production of ATP. The process results in left over low energy electrons that are removed by using them to link H to Oto create water molecules.
In terms of the overall energy flow in aerobic respiration, and the part of photosynthesis that generates ATP (the “light reaction”) you have basically the same sequence of events: High energy electrons hydrogen ions to be pumped across a membrane to produce an H+ gradient. The H+ gradient allows ATP synthetase enzyme to join ADP + P to ATP ATP synthesis in respiration and photosynthesis The difference is the source of the electrons (sugar vs. light acting on water through a photosystem) and the location of the membrane (mitochondrion inner membrane vs. chloroplast thylakoid membrane).
NAD and FAD (not shown) are “pickup trucks” that carry H and electrons to the electron transport chain. NAD is “heavy duty” and carries high energy electrons, while FAD is a “compact” and carries only lower energy electrons.
An aerobic respiration overview (the transistion rxn, between glycolysis and the citric acid cycle is not shown)
Substrate-level phosphorylation is carried out by an enzyme and doesn’t involve electron transport or an H+ gradient.
Four ATPs are “recovered” by substrate-level phosphorylation for a net gain of +2 ATPs.
A slightly more detailed look at the start of glycolysis ENERGY-REQUIRING STEPS OF GLYCOLYSIS glucose ATP 2 ATP invested ADP P glucose-6-phosphate P fructose-6-phosphate ATP ADP P fructose-1,6-bisphosphate (see next slide)
ENERGY-RELEASING STEPS OF GLYCOLYSIS PGAL PGAL NAD+ NAD+ NADH NADH Pi Pi P P P P 1,3-bisphosphoglycerate 1,3-bisphosphoglycerate substrate-level phosphorylation ADP ADP ATP ATP 2 ATP invested P P 3-phosphoglycerate 3-phosphoglycerate P P 2-phosphoglycerate 2-phosphoglycerate H2O H2O P P PEP PEP substrate-level phosphorylation ADP ADP ATP ATP 2 ATP invested pyruvate pyruvate to second set of reactions A slightly more detailed look at the rest of glycolysis
The Transition or Preparatory rxn. next converts pyruvate to acetyl Co A.
PREPARATORY STEPS pyruvate coenzyme A (CoA) NAD+ (CO2) NADH CoA Acetyl–CoA KREBS CYCLE CoA oxaloacetate citrate H2O NADH H2O NAD+ isocitrate malate NAD+ H2O NADH fumarate a-ketogluterate FADH2 CoA NAD+ FAD NADH succinate CoA succinyl–CoA ADP + phosphate group (from GTP) ATP A bit more detailed look at the Citric Acid (TCA) cycle
The Electron Transport Chain and the “Chemi-osmotic” production of ATP. FAD “compact” pickups unload H+ and e- atthe second protein complex (not shown), as a result each NADH delivery results in the production of 3ATPs while each FADH results in the production of 2ATPs.
1 Pyruvate from cytoplasm enters inner mitochondrial compartment. OUTER COMPARTMENT 4 As electrons move through the transport system, H+ is pumped to outer compartment. NADH 3 NADH and FADH2 give up electrons and H+ to membrane-bound electron transport systems. acetyl-CoA NADH Krebs Cycle NADH ATP ATP 5 Oxygen accepts electrons, joins with H+ to form water. ATP 2 Krebs cycle and preparatory steps: NAD+ and FADH2 accept electrons and hydrogen stripped from the pyruvate. ATP forms. Carbon dioxide forms. ATP free oxygen ADP + Pi 6 Following its gradients, H+ flows back into inner compartment, through ATP synthases. The flow drives ATP formation. A detailed overview of the ATP generation process
GLYCOLYSIS 2 ATP outer mitochondrial compartment glucose inner mitochondrial compartment ATP aIn glycolysis, 2 ATP used; 4 ATP form by substrate- levelphosphorylation. So net yield is 2 ATP. 2NAD+ 2 PGAL 2 NADH for in the cytoplasm ATP 2 ATP 2 NADH 2 pyruvate b In Krebs cycle of second stage, 2 ATP form by substrate-level phosphorylation. cytoplasm Electrons and hydrogen from cytoplasmic NADH are shuttled into inner compartment. Two coenzymes already inside transfer the electrons to a transport system. 4 ATP 2 FADH2 c In third stage, NADH from glycolysis used to form 4 ATP by electron transport phosphorylation. 2 CO2 Coenzymes (8 NAD+, 2 FAD total) transfer electrons and hydrogen from remnants of pyruvate to a transfer system. 2 acetyl-CoA 2 NADH ATP 28 6 NADH ATP Electrons flow through transport system KREBSCYCLE ATP 2 FADH2 ATP ATP Transport system pumps H+ to the outer compartment d In third stage, NADH and FADH2 from second stage used to make 28 ATP by electron transport Phosphorylation. ADP + Pi ELECTRON TRANSPORT PHOSPHORYLATION 36 ATP Fig. 7.8, p. 139 At ATP synthases H+ flowing back in drives ATP formation
Respiration includes several ,feedback loops that keep the various pathways in synch with each other.
In addition to producing ATP, the pathways of aerobic respiration act as a central clearing house for intermediary metabolism; removing excess material to proces for ATP production, and providing intermediates to act a “building blocks” for the synthesis of all the compounds a cell needs to make.
Other compounds in food can also be processed to yield ATP, and respiration intermediates can be taken out (reverse the arrows) to provide intermediates for the synthesis of cellular components .
FOOD complexcarbohydrates glycogen proteins fats fatty acids simple sugars,e.g., glucose glycerol amino acids NH3 carbonbackbones glucose-6-phosphate urea PGAL 4 2 ATP GLYCOLYSIS ATP NADH pyruvate acetyl-CoA CO2 NADH KREBSCYCLE NADH FADH2 2 ATP CO2 e- ATP ATP ELECTRON TRANSPORT PHOSPHORYLATION ATP many ATP water H+ e- oxygen Another overview version
Muscle activity demands ATP consumption at accelerated rates which demands faster O2 supply and CO2 clearing from the cardiovascular system
Like muscles forced to work beyond their oxygen supply, yeast growing without adequate oxygen are forced to use an organic compound in place of O2 as a terminal e- acceptor (to unload and recycle NAD); this is defined as fermentation.
