Harvesting Energy: Glycolysis and Cellular Respiration

1
Harvesting Energy Glycolysis and Cellular
Respiration

• Chapter 7

2
ATP

• Adenosine Tri-Phosphate
• Energy carrying molecule
• Receives energy from energy storage molecules
  (such as glucose)
• Transfers energy to needed reactions in the cell
• Ultimately processes energy from photosynthesis

3
Photosynthesis - Glucose Metabolism Relationship

• Photosynthesis
• 6CO2 6H2O light C6H12O6 O2
• Glucose Metabolism
• C6H12O6 6O2 6CO2 6H2O chemical energy and
  heat energy

4
Major Stages in Glucose Metabolism

• Glycolysis
• Glucose is split (into two C3 (pyruvate)
  molecules
• Krebs Cycle
• Remaining bonds (originally from glucose) are
  completely broken (CO2 released)
• Electron Transport
• Elecrtron carriers deliver electrons to
  mitochondrion to produce ATP

5
Glycolysis

• Glucose (C6) is split into two pyruvate molecules
  (C3).
• Two net ATPs are produced.
• Two NADH are produced to carry electrons
  (released from split bonds) to the electron
  transport chain (ETC) to convert electron energy
  to ATP.

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Fig. 7-2
7
Cellular Respiration

• Intermediate step from pyruvate (C3) to acetyl
  molecule (C2) to be carried (by acetyl Co-enzyme
  A) into mitochondrion
• Krebs Cycle
• Electron Transport Chain (ETC).

8
Intermediate Step

• Pyruvate (C3) bond is broken to produce C2
  (Acetyl) and CO2.
• NADH receive electrons from breaking bonds (to go
  to ETC).
• C2 can now enter Krebs Cycle to be broken down
  further.

9
3
Formation of acetyl CoA
1
3
CO2
coenzyme A
coenzyme A
Krebs cycle
2
2
CO2
acetyl CoA
pyruvate
10
Krebs Cycle

• C2 (Acetyl) joins a four carbon compound (C4) to
  form a six carbon compound (C6).
• This six carbon compound is broken down to
  release two carbon bonds (2CO2).
• Three NADH and one FADH2 is used to carry
  electrons to the ETC.
• One ATP is produced from energy released from the
  reactions.

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3
Formation of acetyl CoA
1
3
CO2
coenzyme A
coenzyme A
Krebs cycle
2
2
CO2
acetyl CoA
pyruvate
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Review

• One glucose is split to form two pyruvate (C3)
  molecules.
• NADH and ATP is produced.
• Each pyruvate is further split into acetyl
  molecules (C2), releasing one CO2 for each
  pyruvate.
• Each acetyl molecule (C2) enters the Krebs Cycle
  to be broken down further (the original glucose
  is now completely broken down).
• More NADH and ATP is produced in addition to
  FADH2.

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Electron Transport Chain

• Occurs on the inner membrane of the mitochondrion
  (cristae).
• NADH and FADH2 drops off electrons to be accepted
  by a series of compounds, each receiving
  electrons at a lower energy level (redox
  reactions)
• Energy is release to produce ATP molecules.
• Oxygen is the final electron acceptor as it bonds
  with hydrogens to form H2O

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(matrix)
3
1/2 O2 2H
2e
2e
H2O
1
electron carriers
(inner membrane)
H
H
H
energy to drive
synthesis
2
(intermembrane compartment)
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Tally

• For each NADH run through the ETC, three ATPs
  are produced.
• For each FADH2 run through the ETC, two ATPs are
  produced.
• 2NADH from Glycolysis, 2NADH from Intermediate
  Steps, 6NADH from Krebs Cycles, 2FADH2 from Krebs
  Cycles.

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(cytoplasm)
glucose
2
Glycolysis
2
2
lactate or
pyruvate
2
2
Fermentation
ethanol
CO2
2
CO2
Cellular respiration
CO2
4
2
acetyl CoA
Krebs cycle
2
electron carriers
Electron transport chain
32 or 34
intermembrane compartment
H2O
(mitochondrion)
O2
17
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Total Net Yield

• Because it requires some energy (2ATP) to
  actively transport 2NADH from glycolysis across
  the mitochondrial membrane to get to the ETC, the
  net yield is 36 ATP from one molecule of glucose.
• 38 ATP produced, 36 ATP realized.

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Fermentation

• When O2 is scarce or absent (anaerobic), complete
  breakdown of glucose is not possible.
• Cells must break down glucose to a simple
  molecules (either C2 or C3 compounds) and release
  some CO2.
• Very small amounts of ATP is produced (usually
  2ATP).

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Two Types of Fermentation

• Alcoholic Fermentation
• C6 2ADP 2C2 (alcohol) CO2 2ATP
• Fruits, grains, beer, wine, etc.
• Lactate Fermentation
• C6 2ADP 2C3 (lactate) 2ATP
• Muscle contraction without oxygen
• bacteria

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Glycolysis followed by alcoholic fermentation
regeneration
2
2
2
(glycolysis)
(fermentation)
glucose
ethanol
CO2
pyruvate
2
2
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Glycolysis followed by lactate fermentation
regeneration
2
2
(glycolysis)
(fermentation)
lactate
glucose
pyruvate
2
2
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Alcoholic Fermentation - yeast and bread rising
Lactate Fermentation Muscle contraction without
adequate oxygen
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Summary

• Glycolysis, the intermediate step (pyruvate to
  acetyl), and fermentation occurs in the cytoplasm
  of a eukaryotic cell.
• Krebs Cycle and ETC occurs in the mitochondrion
  (Krebs in the matrix and ETC on the cristae).
• 2ATP is produced anaerobic (glycolysis or
  fermentation).
• 36ATP is produced aerobic (glycolysis Krebs
  ETC)

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(cytoplasm)
glucose
2
Glycolysis
2
2
lactate or
pyruvate
2
2
Fermentation
ethanol
CO2
2
CO2
Cellular respiration
CO2
4
2
acetyl CoA
Krebs cycle
2
electron carriers
Electron transport chain
32 or 34
intermembrane compartment
H2O
(mitochondrion)
O2
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Key Terms

• adenosine triphosphate (ATP)
• cellular respiration
• chemiosmosis
• electron transport chain
• fermentation
• flavin adenine dinucleotide (FADH2)
• glycolysis

• intermembrane compartment
• Krebs cycle
• matrix
• mitochondria
• nicotinamide adenine dinucleotide (NADH)
• pyruvate