Study guide 7
Cell Structure & Function
Respiration and Fermentation
Glycolysis and Fermentations
Heterotrophic organisms get energy from free-energy-rich nutrients like
do this by fermentation (glycolysis, in part), while the rest of us do it by
electron transport/oxidative fermentation
energy of nutrients is captured by
of the cell
(i.e., free energy for nearly all work a cell does is fueled directly by ATP.
The free energy in
ATP is in turn, used to fuel endergonic (free energy-requiring reactions) in cells such as the
contraction of muscles, the movement of cilia and flagella, or even the polymerization of
monomers into macromolecules.
The hydrolysis of a phosphate from ATP is accompanied by
the transfer of the phosphate to other molecules.
In metabolic pathways, such phosphorylated
molecules are “activated”, to undergo exrergonic reactions (
In other examples, the
phosphate is transferred to a protein, changing its shape and therefore its activity state (
The free energy in nutrients is released when they are oxidized; this free energy is then captured
in ATP molecules.
Recall that pre-biotic redox reactions resulted in the reduction of inorganic and simple organic
molecules, to make the free-energy rich nutrients of the primordial soup.
involve the transfer of electrons: molecules that give up or lose electrons are oxidized while
those that gain them are reduced (
). You can track the movement of electrons from
glucose (a key energy nutrient) to oxygen in
Organisms use the redox reactions of
fermentation and respiration to get free energy from these nutrient molecules.
molecules or their intermediates are oxidized, electron carriers like NAD+ are reduced (
electron carriers like NADH carry much of the free energy from nutrient
oxidations; you can expect that this free energy will end up in ATP!
The 4 steps of respiration
evolved to take energy from nutrients, hold it in reduced electron carriers and finally put it into
ATP, are summarized in
Because it can make ATP anaerobically (without oxygen), glycolysis may be the oldest
biochemical (metabolic) pathway. As we will see, the other pathways (the Krebs cycle,
electron transport, oxidative phosphorylation) evolved later as part of
levels of oxygen increased in the atmosphere.