four important events occur in the glycolytic pathway 1.substrate level phosphorylation: the...
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Four Important Events
Occur in the Glycolytic Pathway
1. Substrate level phosphorylation: the transfer of phosphate groups from substrates to ATP
2. Breaking of a six-carbon molecule (glucose) into two three-carbon molecules of pyruvate
3. The reduction of two coenzymes of NAD to NADH
4. The capture of energy in ATP
Fermentation• Pyruvic Acid
– metabolized in the absence of oxygen– NAD must be recycled– NAD passes electrons to other
molecules
• Types of fermentation– Lactic acid
• Pyruvic acid converted to lactic acid• uses electrons from NAD
– Alcoholic• carbon dioxide released from pyruvic acid• Acetaldehyde formed• reduced to ethanol
Lactic Acid Fermentation: Pyruvic acid reduced to lactic acid by NAD from glycolysis
Alcoholic Fermentation: Carbon dioxide removed from pyruvic acid to acetaldehyde; Acetaldehyde reduced to ethyl alcohol by NAD
Results of Glucose Fermentation
• Natural waste products useful to humans
– Fermented beverages– Bread– Cheese– Yogurt
• Infectious microbes may cause disease
Fermentation Pathways
Aerobic Respiration
• Glycolysis yields 2 ATP’s net
• Partial oxidation of carbon atoms
• Starts with glycolysis • Yields 36-38 ATP’s
• Complete oxidation of substrate molecules to C02 in the Krebs Cycle
Anaerobic Respiration
Transition to the Krebs cycle: Pyruvic acid loses CO2 & gets oxidized by NAD; two-carbon acetyl group attaches to coenzyme A, forming acetyl-CoA.
The Reactions of the Krebs Cycle
What has been accomplished in theKrebs Cycle?
• 8 reactions instead of just 1• Each reaction has a separate reactant-specific enzyme• The initial reactants are two 2-carbon molecules of acetyl
Co-A and the final products are four 1-carbon molecules of CO2 .
• Transfer of electrons and/or H+ to coenzymes – 3 pairs to NAD and 1 to FAD for each turn of the cycle
• One ATP molecule produced for each turn of the cycle • The cycle turns two times for each molecule of glucose
because glucose has been converted to two molecules of acetyl Co-A
• The cycle regenerates the starting molecule, oxaloacetate
Why is Krebs a Cycle?
• Oxaloacetic acid combines with acetyl-CoA in the first step
• Oxaloacetic acid is regenerated at the end
What happens to the Coenzymes?
• They must be reoxidized!– Their chemical bonds have stored chemical energy.– Coenzymes are in short supply.– Must be available to continue their oxidation work in
the Krebs Cycle
http://www.youtube.com/watch?v=26EE3jG5thM&feature=related
Waterfall model of the electron transport chain
• As electrons pass from carrier to carrier, they decrease in energy.
• Some of the energy they lose is harnessed to make ATP.
The Electron Transport Chain
• The electron transport chain performs two functions:
– Accepts electrons from NADH and FADH2 & transfers them to electron acceptors
– Uses the energy released during the electron transfers to pump H+ across the inner mitochondrial membrane to the intermembrane space creating a concentration gradient
Enzyme Complexes Involved in Electron Transport
Oxidation/reduction enzymes:1. NADH dehydrogenase2. Flavoproteins (FAD) 3. Iron-sulfur proteins4. Cytochromes5. Quinones (lipid-soluble)
http://www.youtube.com/watch?v=xbJ0nbzt5Kw&feature=related
Electron Transport Chain
• Transfers electrons from one substrate to another and finally to oxygen
• Pumps H+ across the inner mitochondrial membrane into the inter-membrane space
• Oxygen is the final electron and hydrogen acceptor!
Chemiosmosis
• The electron transport chain creates a H+ gradient potential across the inner mitochondrial membrane
• ATP Synthase allows H+ back across the membrane
• ATP is produced by a proton motive force (pmf) when H+ pass through ATP Synthase and cause ADP + P to form ATP.
http://lecturer.ukdw.ac.id/dhira/Metabolism/ETLP.html
Oxidative Phosphorylation
ATP formation involving molecular oxygen and chemiosmosis
http://www.youtube.com/watch?v=26EE3jG5thM&feature=related
• What part of the electron transport chain is represented by the marbles being pushed upward?
– The hydrogens being pumped into the inter-membrane space
How does electronegativity play a part in the electron transport chain?
– Each electron acceptor in the chain is more electronegative than the previous one
– the electrons move from one electron transport chain molecule to the next, falling closer and closer to the nucleus of the last electron acceptor.
Where do the electrons for the electron transport chain come from?
• NADH and FADH2 which got their electrons from glucose originally, in the previous two phases of cell respiration.
Why does FADH2 drop its electron onto a different initial acceptor than NADH?
• It has a different electronegativity.
• FADH2 is more electronegative and therefore the initial acceptor for FADH2 must be stronger in order to pull the electrons away.
What molecule is the final electron acceptor?
• Water is made from the splitting of an oxygen gas molecule. Each oxygen atom grabs– two electrons from the electron transport chain and– two hydrogen ions from the inter-membrane space.
• What is consumed during this process?
• Oxygen gas
What is gained by this process?
• A chemiosmotic gradient of H+ ions inside the inter-membrane space.
The electron transport chain does not generate ATP directly, so what good does it do?
• It generates a chemiosmotic gradient that will eventually generate ATP.
How does this gradient generate ATP?
• A special protein, ATP Synthase, embedded in the inner membrane can use the flow of hydrogen ions, H+, to phosphorylate ADP molecules.
How does the specialized membrane protein work?
• It turns mechanically like a rotary motor
• As the hydrogen ions, H+, rush through the protein channel, it causes chemical energy to be converted into mechanical energy
• This energy drives a phosphorylation reaction.
• This is called oxidative phosphorylation.
Is cell respiration endergonic or exergonic?
• Exergonic – energy is released.
Is it a catabolic or anabolic reaction?
• Catabolic – a molecule is being broken down into smaller molecules
If one molecule of ATP holds 7.3 kcal of potential energy, how much potential energy does one molecule of glucose
produce in cell respiration?
• At its maximum output:
38 X 7.3 kcal = 277.4 kcal
One molecule of glucose actually contains 686 kcal of potential energy. Where does the remaining energy go
when glucose is oxidized?
• It is lost as heat which is why we’re warm.
What is the net efficiency of cell respiration if glucose contains 686 kcal
and only 277.4 kcal are produced?
• 277.4 / 686 x 100 = 40%
How does this rate of efficiency compare to energy capture processes
that you see in everyday life?
• Incandescent light bulb = 5% efficient
• Electricity from coal = 21% efficient
• Car engines = 23% efficient
Define cellular respiration.
• Cellular respiration is the release of energy from food by oxidation.
Compare anaerobic and aerobic respiration.
Aerobic Respiration
• Glycolysis yields 2 ATP’s net
• Partial oxidation of carbon atoms
• Starts with glycolysis • Yields 36-38 ATP’s
• Complete oxidation of substrate molecules to C02 in the Krebs Cycle
Anaerobic Respiration
Why doesn’t the reaction stop once the ATP’s are produced from glycolysis
leaving the oxidized glucose in the form of pyruvate?
• Because the reactions that produce CO2 + alcohol or lactic acid are needed to reoxidize NADH. Without this the lack of NAD+ would stop glycolysis.
Given what you know about the process of fermentation, what are some of the requirements
for making wine or beer?• A culture of yeast or other anaerobic
organisms
• An oxygen-free environment so the organisms are forced to perform only glycolysis
• A source of glucose or fructose
Total Energy Released
“The oxidation of glucose to carbon dioxide releases approximately 277.4 kcal of energy. If all of this energy is released at one time, then most of it would be lost as heat. Burning the energy all at once would be akin to igniting your gas tank in order to run your car, rather than burning small amounts of gasoline slowly in the engine. If the energy of glucose is released slowly, in several small steps, then the potential energy available could be captured at each small step, just as the gasoline energy is captured (to move a car) in a slow release rather than in a single, explosive release.”
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