Energy Releasing Pathways

(Harvesting Chemical Energy)
• Glycolysis
• Fermentation
• Aerobic respiration
 Glycolysis
 Redox Reaction
 Oxidation: loss of e- (glucose)
 Reduced: Gain of e- (Co2)
 Takes
place in the cytosol
 1, 6 carbon molecule of glucose goes
through a series of chemical reactions
catalyzed by specific enzymes to
produce 2, 3 carbon molecules of
pyruvic acid.
 NAD+ similar to NADP+
 NAD+ carry electrons and Hydrogen
ions (NADH)
1 Glucose
 2 ATP
 2 NAD+
 4 ADP + 2Phospates
Net 2 ATP
2 Pyruvic acid
Organic Compound
no oxygen
Aerobic Respiration
Prokaryotes and protists in anaerobic
habitats (mainly unicellular organisms)
 Does not produce ATP
 Many Fermentation pathways differ in
the types of enzymes and final products
 Two most common produced are lactic
acid and ethyl alcohol
Occurs in muscle cell when strenuous
exercise causes muscle cells to use up all
the oxygen available to them. They switch
to anaerobic respiration and lactic acid
builds up in the cells, changing the acidity
of the cytoplasm.
 Increased acidity decreases the cells ability
to contract causing cramps and fatigue.
 Eventually it diffuses out of cell into blood
stream and is transported to liver where it is
converted back into pyruvic acid.
 Used to make cheese and yogurt
Used by some plants and unicellular
organisms such a yeast
 Bread making
Requires O2
Approximately 20 times as much ATP
produced then glycolysis
Two major stages: Krebs cycle and the
electron transport chain
In eukaryotic cell takes place in the
Krebs cycle occurs in the mitochondrial
Electron transport chain occurs in the inner
Pyruvic acid enters the mitochondrial
 It reacts with a molecule called
coenzyme A (CoA) to form acetyl CoA
 CO2 and NADH and H+ are produced
Step 1: Acetyl CoA combines with
Oxaloacetic acid to form citric acid
(regenerates CoA)
Step 2: Citric acid releases CO2 and a H
atom that combines with NAD+ to form NADH
+ H+ to form 5 carbon compound.
Step 3: 5 carbon compound releases CO2
and a Hydrogen atom (combines with NAD+
to form NADH + H+) to form a 4 carbon
compound. A molecule of ATP is formed.
Step 4: 4 Carbon compound releases a
hydrogen atom ( combines with FAD to
Form FADH2) and is converted to another
4 carbon compound.
 Step 5: The 4 carbon compound
releases a hydrogen atom and is
(combines with NAD+ to form NADH +
H+)converted back into Oxaloacetic
1 glucose molecule = 2 turns of the Krebs
 6 NADH
 2 FADH2
 2 ATP
 4 CO2
Most of the energy from glucose still
have not been transferred to ATP
 10 NADH and the 2 FADH2 produced so
far to drive the electron transport chain

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