UNIT 2: Metabolic Processes
Chapter 3: An Introduction to Metabolism
3.4: Food and Fuel
pg. 124 - 165
pg. 151 - 155
Glucose is the energy molecule that runs the cell. The molecule contains a
great deal of potential energy in its bonds (C-H).
Energy Changes during Oxidation
Oxidation occurs when an atom or molecule loses electrons to another atom
or molecule.
Oxygen has a high electronegativity; therefore it is an ideal electron acceptor
in the process of cellular respiration. The opposite of oxidation is called
reduction, the gain of electrons.
Oxidation – is a reaction in which a molecule loses electrons.
Reduction – is a reaction in which a molecule gains electrons.
Oxidizing Agent – is the atom or molecule that gains the electrons.
Reducing Agent – is the atom or molecule that loses the electrons.
Rapid Combustion and Controlled Oxidation
Combustion in a cell, burning of a fuel like glucose, will release
too much free energy at a high temperature. This will destroy the
cell and all the free energy is released as thermal energy.
The cell has an alternative to rapid oxidation of glucose, resulting
in the same products, but less of a temperature increase. This
reaction occurs in a series of steps, releasing small amounts of
manageable free energy in the cell.
In the cell, the oxidation of glucose occurs through a series of
enzyme-catalyzed reactions, or steps, releasing small manageable
amounts of free energy, maintaining temperature. The energy
release is transferred to energy-carrying molecules to the next step
in the reaction.
Figure 4: A comparison of the oxidation of glucose by a) controlled and b) rapid
combustion.
Energy Carriers
Redox reaction – is an electron transfer reaction.
Cellular respiration is a redox reaction. Glucose is oxidized by
oxygen to form carbon dioxide and water. This reaction is assisted
by enzyme called Dehydrogenase. This reaction is assisted by
energy carriers, coenzymes, such as; nicotinamide adenine dinucleotide (NAD+).
Dehydrogenase supports the removal of 2 hydrogen atoms, 2
electrons, from one substrate and combines 1 hydrogen atoms and
2 electrons to NAD+ reducing it to NADH and releasing one H+
into the cytosol of the cell. NADH is later used to synthesize ATP.
Dehydrogenase – is an enzyme that oxidizes a substrate and transfers
hydrogen ions to an acceptor.
NADH – is the reduced form of the coenzyme nicotinamide adenine dinucleotide. (NAD+)
Figure 5: Structure if electron carrier NAD+ and its fully reduced form, NADH.
Chapter 3: Summary
pg. 158
Chapter 3: Self-Quiz
pg. 159
Chapter 3: Review
pg. 160 - 165