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25 Cards in this Set

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What happens after glycolysis?
After glucose is broken down to pyruvic acid, pyruvic acid can be channeled into either
Fermentation OR Cellular Respiration
Aerobic respiration
-Requires oxygen
-Final electron acceptor is O2
Anaerobic respiration
-No oxygen
-Final electron acceptor is an inorganic molecule other than O2
Aerobic Respiration
Tricarboxylic acid (TCA) cycle
-Kreb's cycle or citric acid cycle
-A large amount of potential energy stored in acetyl CoA is released by a series of redox reactions that transfer electrons to the electron carrier coenzymes (NAD+ and FAD)
Acetyl CoA (Figure 8.20)
Where does it come from?
Pyruvic acid, from glycolysis, is converted to a 2-carbon (acetyl group) compound (decarboxylation)
The acetyl group then combines with Coenzyme A through a high energy bond
NAD+ is reduced to NADH
TCA cycle (Figure 8.20)
For every molecule of glucose (2 acetyl CoA) the TCA cycle generates
4 CO2
electron transport chain
- 2 NADH from glycolysis
- 2 NADH from pyruvic acid to acetyl CoA conversion
- 6 NADH and 2 FADH2 from the TCA cycle
The electron transport chain indirectly transfers the energy from these coenzymes to ATP
The electron transport chain
Sequence of carrier molecules capable of oxidation and reduction
Electrons are passed down the chain in a sequential and orderly fashion
Energy is released from the flow of electrons down the chain
This release of energy is coupled to the generation ATP by oxidative phosphorylation
Membrane location of the ETC (Figure 8.21 & 8.23c)
The electron transport chain is located in;
- the inner membrane of the mitochondria of eukaryotes
- the plasma membrane of prokaryotes
The ETC players
Three classes of ETC carrier molecules
-Contain a coenzyme derived from riboflavin
-Capable of alternating oxidations/reductions
-Flavin mononucleotide (FMN)
-Have an iron-containing group (heme) which can exist in alternating reduced (Fe2+) and oxidized (Fe3+) forms
Coenzyme Q (Ubiquinone)
-Small non protein carrier molecule
Are all ETCs the same?
Bacterial electron transport chains are diverse
Particular carriers and their order
Some bacteria may have several types of electron transport chains
Eukaryotic electron transport chain is more unified and better described
All have the same goal to capture energy into ATP
The mitochondrial ETC (Figure 8.22)
The enzyme complex NADH dehydrogenase starts the process by dehydrogenating NADH and transferring its high energy electrons to its coenzyme FMN
In turn the electrons are transferred down the chain from FMN to Q to cytochrome b
Electrons are then passed from cytochrome b to c1 to c to a and a3 with each cytochrome reduced as it gains electrons and oxidized as it loses electrons
O2, the terminal electron acceptor (Figure 8.22)
Finally, cytochrome a3 passes its electrons to O2 which picks up protons to form H2O
Important features of ETC (Figure 8.22)
Electron transfer down the chain is accompanied at several points by the active pumping of protons across the inner mitochondrial membrane
This transfer of protons is used to generate ATP by chemiosmosis
FADH2 from the TCA cycle also feeds into the electron transport chain but at a lower level, so less energy is generated
The ETC sets up a proton gradient (Figure 8.23a)
As energetic electrons are passed down the ETC some carriers (proton pumps) actively pump H+ across the membrane.
Proton motive force results from an excess of protons on one side of the membrane
Generation of ATP by chemiosmosis (Figure 8.23b)
Protons can only diffuse back along the gradient through special protein channels that contain the enzyme ATP synthase.
ATP synthase uses the energy released by the diffusion of H+ across the membrane to synthesize ATP from ADP
ETC drives chemiosmosis (Figure 8.22)
NADH generates 3 ATP
FADH2 generates 2 ATP
Aerobic respiration (Figure 8.17)
Complete oxidation of 1 glucose molecule generates 38 ATP in prokaryotes
2 from each of glycolysis and the TCA cycle by substrate level phosphorylation
34 from oxidative phosphorylation as a result of 10 NADH and 2 FADH2 from glycolysis and the TCA cycle
Eukaryotes only produce 36 ATP from aerobic respiration
Anaerobic Respiration
Like aerobic respiration, it involves glycolysis, the TCA cycle and an electron transport chain
But The final electron acceptor is an inorganic molecule other than O2
Some bacteria use NO3- and produce either NO2-, N2O or N2 (Pseudomonas and Bacillus)
Desulfovibrio use SO42- to form H2S
Others use carbonate to form methane
The amount of ATP generated varies with the pathway
Only part of the TCA cycle operates under anaerobic conditions
Not all ETC carriers participate in anaerobic respiration
ATP yield never as high as aerobic respiration
Releases energy from sugars or other organic molecules
Does not require O2
Does not use the TCA cycle or ETC, but does use glycolysis
Uses an organic molecule as the final electron acceptor
Produces only small amounts of ATP (from glycolysis).
Most of the energy remains in the end product
Recycling the NAD
In fermentation, pyruvic acid or its derivatives are reduced by NADH to fermentation end products
Ensures recycling of NAD+ for glycolysis
Why bother with fermentation?
Fermenting bacteria can grow as fast as those using aerobic respiration by markedly increasing the rate of glycolysis
Fermentation permits independence from molecular oxygen and allows colonization of anaerobic environments
Alcohol fermentation
-Alcohol fermentation by the yeast Saccharomyces is responsible for some of the better things in life
-CO2 produced causes bread to rise
-Ethanol is used in alcoholic beverages
Acid fermentation
-Only lactic acid
-Streptococcus and Lactobacillus
-Mixture of lactic acid, acetic acid and CO2
-Can result in food spoilage
-Can produce Yogurt from milk, Sauerkraut from fresh cabbage, Pickles from cucumber
Metabolic pathways of Energy Use
The complete oxidation of glucose to CO2 and H2O is considered an efficient process
But, 45% of the energy from glucose is lost as heat
Cells use the remaining energy (in ATP) in a variety of ways
- E.g., active transport of molecules across membrane or flagella motion
- Most is used for the production of new cellular components
Integration of metabolic pathways
Carbohydrate catabolic pathways are central to the supply of cellular energy in most microorganisms
However, rather than being dead end pathways, several intermediates in these pathways can be diverted into anabolic pathways
This allows the cell to derive maximum benefit from all nutrients and the metabolites in the cell pool
Amphibolism-integration of catabolic and anabolic pathways to improve cell efficiency
Amphibolic view of metabolism (Figure 8.26)
Principle sites of amphibolic interaction
- glyceraldehyde-3-phosphate
- pyruvate
TCA cycle
- acetyl-CoA
- oxaloacetic acid
- alpha-ketoglutaric acid