Balanced equation for the complete oxidation of glucose by O2

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Balanced equation for the complete oxidation of
glucose by O2
Exergonic flow of electrons and protons to O2
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Four steps

• Glycolysis in the cytoplasm
• Partial oxidation of glucose to pyruvate
• Citric acid cycle (Krebs cycle) in the
  mitochondrial matrix
• Partial oxidation of pyruvate to acetyl CoA
• Complete oxidation of acetyl CoA to CO2
• Oxidation of the oxidants, NADH and FADH2 by
  electron transfer within the inner mitochondrial
  membrane.
• Reduction of O2 to H2O.
• Generation of proton gradient across inner
  mitochondrial membrane used to make ATP by (4)
  oxidative phosphorylation.

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Glycolysis
Link
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Gly-6 and Gly-7 p. 230
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carbon oxidation number
-4
-2
0
2
4
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NAD and NADH the principal electron carriers
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13_06_NADH _ATP .jpg
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• Glyceraldehyde-3-P is oxidized and phosphorylated
  to 1,3 bisphosphoglycerate
• The oxidation of an aldehyde to an acid is
  exergonic
• The energy is used to increase the instablity of
  the phosphate on the 1,3 bisphosphoglycerate
• The high energy phosphate is then transferred to
  ADP exergonically
• Oxidation drives ATP production at the level
  substrate-enzyme interaction

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Second substrate-level phosphorylation
Gly-10 p. 230
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13_07_Phosphate_bond.jpg
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What would be the net yields of ATP from one
molecule of glucose-6-P?

• 2
• 3
• 4
• 5

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Discussions of glycolysis refer to pyruvate, not
pyruvic acid, because

• Pyruvate is the conjugate base form that
  predominates at cell pH.
• Pyruvate is simply shorthand for pyruvic acid.
• Pyruvate is incorrect pyruvic acid is the
  predominate conjugate acid form at cell pH.
• Either term can be used because the pKa equals he
  cell pH.

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In the critical oxidation of 3-phosphoglyceraldehy
de to 1,3- bisphosphoglycerate, which is not a
product?

• ATP
• NADH H
• Water

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Glucose oxidation produces numerous acids. In
addition to buffers, which of the following would
help regulate cellular pH?

• Na-H antiporter
• Na-H symporter
• K-H antiporter
• Ca-H symporter

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Glycolysis will quickly stop because all of the
NAD is all reduced to NADH. How can glycolysis
continue?

• NADH reoxidized by oxygen at the end of electron
  transfer
• In the absence of oxygen, pyruvate may be reduced
  to
• lactate (exercising muscle)
• ethanol (yeast)

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LDH
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13_04_02_Pyruvate_fermt.jpg
PDC
ADH
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Key points about glycolysis

• Glycolysis is the partial oxidation of one
  molecule of glucose to two molecules of pyruvate
  in the cytoplasm.
• The oxidant is NAD and two NADH2 molecules are
  produced per molecule of glucose.
• Two ATPs are expended in the first three steps to
  phosphorylate glucose.
• 1,6 bisphosphofructose is cleaved to two
  molecules of 3-P glyceraldehyde.
• 3-P glyceraldehyde is oxidized and phosphorylated
  to 1,3 bisphosphoglycerate. (Step 6). This is a
  very important step since it uses the energy
  released from the oxidation (aldehyde to acid) to
  increase the energy of a phosphate ion.

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• In step 7, one high-energy phosphate is
  transferred from the substrate to ADP to form
  ATP. This is the break-even step.
• In step 10, a second high-energy phosphate is
  transferred from PEP (phosphoenol pyruvate) to
  ADP. This is the go-ahead step.
• In order for glycolysis to continue, NAD must be
  regenerated. This can be done by oxidizing NADH
  via the electron transfer system (if oxygen is
  present) or by the reduction of pyruvate to
  lactate or ethanol.
• Ethanol can be oxidized in two steps to acetate
  (acetyl CoA). The intermediate is acetaldehyde
  which is the chemical that makes ethanol so toxic.

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All roads lead to vinegar

• Pyruvate is oxidized to acetyl CoA
• Fat is oxidized to acetyl CoA
• Ethanol and lactate are oxidized to acetyl CoA
• Several amino acids are converted to acetyl CoA

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13_08_acetylCoA_CO2.jpg
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Disulfiram (Antabuse)
ALDH-2 with high Km (common in orientals)
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Disulfiram (Antabuse) plus even small amounts of
alcohol produces flushing, throbbing in head and
neck, throbbing headache, respiratory difficulty,
nausea, copious vomiting, sweating, thirst, chest
pain, palpitation, dyspnea breathing
difficulty, hyperventilation, tachycardia,
hypotension, syncope light headedness, marked
uneasiness, weakness, vertigo, blurred vision,
and confusion. http//www.healthyplace.com/medic
ations/disulfiram.htm

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Citric Acid (Krebs) Cycle
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(No Transcript)
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Citric Acid (Krebs) Cycle
Electron transfer Oxidative phosphorylation
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As pyruvate is prepared for the citric acid
cycle, it undergoes

• Reductive carboxylation
• Oxidative decarboxylation
• Oxidative carboxylation
• Reductive decarboxylation

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Which of the following is NOT true of the citric
acid cycle?

• There are three oxidations
• There are two decarboxylations
• There is one substrate-level phosphorylation
• Acetate condenses with 4C-oxaloacetate
• FAD is an oxidant

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13_23_precursors.jpg
CAC is amphibolic both anabolic and catabolic
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Citric acid cycle intermediates are catalytic,
not stoichiometric.

• Acetyl-CoA 2CO2.
• Because the CAC is a cycle, there can be no net
  breakdown of intermediates the reactant is
  reformed by the cycle!
• The higher the concentration of CAC
  intermediates, the higher the concentration of
  oxaloacetate (OAA). This increases the rate of
  pyruvate (acetyl-CoA) entry. The intermediates
  are catalytic.

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Pyruvate
Ketone bodies
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ketosis
acidosis
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Pyruvate
Ketone bodies
CO2
Pyruvate carboxylase
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The anaplerotic step

• Acetyl CoA can only enter the Krebs cycle by
  condensing with OAA
• When the citric acid cycle intermediates run
  down, the cycle must be filled up
• Pyruvate CO2 OAA
• Acetyl CoA is an allosteric activator of pyruvate
  carboxylase

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• When does ketoacidosis occur?
• starvation (utilization of fat reserves)
• diabetes (sugar cannot enter the cell due to the
  lack of insulin or failure of insulin to work)
• Dr. Atkins Diet. Ketosis is a condition
  earnestly to be desired.

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