Catabolic Pathways and Glycolysis
• The ability to do that work depends on catabolic process that
harvest the potential energy found in organic molecules. The 2
catabolic processes that occur in organisms are:
– fermentation (breakdown without O2)
– cellular respiration (breakdown with O2).
Redox reactions power the production
of ATP
• Redox Reactions power the production of
energy within the cell.
Reduction Reactions
• Reduction - the gain of
negative charge on an atom
as it becomes more negative
– can occur through transfer
of an e- or through unequal
sharing of the e– the atom or molecule that
donates the charge is the
reducing agent
– atoms rich in H make great
reducing agents because
they are the least
electronegative and are
oxidized easily - called
"hilltop" electrons
NAD+ + 2H g NADH + H +
• 2e- gained by NADH to be used in
a later reaction
• H+ to be used to establish an ion
gradient within the mitochondria
Oxidation Reactions
• Oxidation - the loss of negative charge on an atom as it becomes
more positive
– can occur through the loss of an e- or the movement of an e- away
from the atom
– the atom or molecule that accepts the charge is the oxidizing agent
• A + B g A+ + B- (A is the reducing agent, B is the oxidizing agent)
• Xe- + Y g X + Ye- (Xe- is the reducing agent, Y is the oxidizing agent)
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Stages of Cellular Respiration
Glycolysis
Citric Acid Cycle
Oxidative Phosphorylation
• primary catabolic pathway
used in organisms to produce
energy (ATP)
– although fats & proteins can be
broken down, glucose is the
primary fuel used
– energy gained is through the
transfer or relocation of
electrons throughout the
process (redox)
Cellular
Respiration
• C6H12O6 + 6O2 g 6CO2 + H2O +
Energy (ATP & Heat) DG = -686
kcal/mol
– this reaction C & H are being
oxidized by O2 to yield the energy
for the production of ATP
• NAD+ is an oxidizing agent in
cellular respiration as is accepts a
H atom & becomes NADH + H+
(the enzyme dehydrogenase
removes 2 e- to energize the NADH
complex)
• the energy stored in the bonds is
later used to create ATP (& water
as oxygen accepts the used H)
Cellular
Respiration
• Catabolic process that degrades glucose into 2
Pyruvate molecules + 2 H2O molecules
– occurs in the cytosol
– requires the input of 2 ATP molecules and produces
4 ATPs (net of 2)
– 2 NAD+ are reduced to 2 NADH + 2 H+ (net gain of
4e-)
• Pyruvate is then transported into the mitochondria
to begin the Citric Acid Cycle
• Reaction does not require oxygen (anaerobic
process)
– No CO2 is produced!
– All C atoms are present in the final products of the
reactions
• Simplified equation
– Glucose + 2ATP + 2NAD g 2Pyruvate + 4ATP +
2NADH + 2H+
– The left side is called the Energy Investment phase
– The right side is called the Energy Payoff phase
• Complex equation
Glycolysis