Biology Lecture No. 10: Cellular Respiration I
Wednesday February 8 , 2012
-Respiration is an overall exergonic process which yields a negative change in Gibbs’ Free Energy (-∆G).
-Out of all metabolic processes, cellular respiration has a fundamental role in biological function. It
occurs in all known organisms.
-Respiration consists of two major types of metabolic pathways: Catabolic pathways and anabolic
-Catabolic pathways involve the breakdown of molecules and release of free energy. The overall
pathway is exergonic (-∆G).
-Anabolic pathways involve the synthesis of more complex molecules out of simpler forms. Examples of
such pathways include all biosynthetic pathways like photosynthesis. The overall pathway is endergonic
ATP & ADP Cycle:
-Catabolic pathways drive the conversion of ADP + Pi to ATP.
-When the free energy of ATP is coupled with anabolic pathways, the energy is released and leaves
behind the original reactants, ADP and Pi, waiting to begin the cycle again.
-Recall that food can be the equivalent of fuel as molecules for consumption (like glucose, amino acids
and fatty acids) contain lots of carbon-hydrogen bonds.
-Especially in glucose, there is a lot of free energy associated with such molecules. In the reaction for
cellular respiration, C6H12 6 + 6O 2 6CO 2 + 6H O2 glucose is oxidized to CO an2 oxygen is
reduced to water. It can be said that CO is much more oxidant than glucose.
Respiration & Controlled Combustion:
-Cellular respiration essentially comprises of extracting energy from glucose by way of controlled
combustion. The change in free energy is the same regardless of whether the combustion of glucose is
controlled or not (686kCal/mol).
- The only difference is that respiration has many small activation energies where direct burning has just
one large E a That is because respiration involves transferring energy to electron carriers and
uncontrolled combustion has all the energy released as heat, none is stored. NAD As An Electron Shuttle:
-Where NADP transports electrons in anabolic and biosynthetic reactions, NAD (Nicotinamide adenine
dinucleotide) is the main energy carrier in catabolic reactions like cellular respiration.
(NAD + 2e + H + NADH)
Overview Of Respiration:
-Cellular respiration comprises of three main processes in this particular order: Glycolysis
(Breakdown/Oxidation of Glucose), Citric Acid Cycle (Production of CO ), a2d the Electron Transfer
System & Oxidative Phosp