This is a summary of the energy metabolism in the cell. The subjects that are discussed are ATP, Ion motive forces, Glycolysis, Pyruvate oxidation, Citric acid cycle, Oxidative phosphorylation, Respiratory chain/electron transport chain, ROS formation, ATP as a drug target, ATP in synapses, Warbur...
Experimental Cell Biology: Energy metabolism
Cells need energy for metabolism for To produce energy from nutrients a few processes
biosynthesis, transport and movement. ‘The are involved.
energy for these processes is provided by the • Substrate-level phosphorylation (glycolysis)
breakdown of molecules in the diet such as • Citric acid cycle
carbohydrates, lipids and proteins. The energy • Oxidative phosphorylation
derived from the diet molecules is stored as
energy currencies. Common currencies of Glycolysis
energy in living cells are: Glycolysis is the metabolic pathway that converts
• Adenosine triphosphate (ATP) glucose into pyruvate. During this process, some
• Ion motive forces across membranes enzymes catalyse the reaction. First, there is the
energy required, 2 ATP gets used up whereas 4
ATP ATP + 2 pyruvates + 2 NADH comes out. The
When ATP is consumed in metabolic processes, it process happens in the cytosol and is very fast. It
converts to ADP or AMP, due to the loss of one or is also a very tricky process because ATP is
two phosphate groups. ATP is used for needed and this will not be possible when the cell
endergonic reactions, which means that the is deprived of energy.
reaction requires energy to proceed. What can
drive endergonic reactions, are: ion gradients
such as protons, sodium and potassium. 2x
Researchers have studied how a eukaryotic model
can cope with the change of an environment with
high glucose levels and how the system fails which
results in metabolic malfunctioning and growth
arrest. The growth of yeast was measured
through flow cytometry and colony plating of a
Ion motive forces wild type and mutants that were unable to transit
The ion motive force is the sum of electrical and properly to excess glucose. The results showed
chemical potential differences (ion gradient) that the failure to cope with glucose was caused by
across the cell membrane and is the driving imbalanced reactions in glycolysis. In the failure
force of ATP synthesis (ATP synthase). When mode, the first steps of the glycolysis carry more
protons flow through a channel in the enzyme flux than the downstream steps which resulted in
the movement spins the protein (sort of like a constant low levels of ATP. In the mutants, only
wind turbine). This movement provides the 0,01% of the cells started growing and in the
energy to add a phosphate group to ADP to wildtype, 93% of the yeast cells started growing.
form ATP. Like most enzymes, but unlike most Models showed that the dynamics of phosphate is
ATP synthases, this enzyme can run a key determinant in a successful transition to
backwards within the cell. This ATP hydrolysis glucose and that the phosphate release through
can be the driving force to cause the enzyme to ATP hydrolysis reduces the probability of
release protons out of the mitochondria. The reaching an imbalanced state.
“ leak” back across the inner membrane is
needed to keep stimulating the membrane Pyruvate oxidation
potential to maintain the activity of the Pyruvate oxidation takes place in the
respiratory chain. mitochondrial matrix. During the pyruvate
oxidation, pyruvate gets converted into acetyl
CoA so it can enter the citric acid cycle. Pyruvate
is modified by the removal of a carboxyl Group
followed by oxidation and then attached to
Coenzyme A, which yields NADH. (Next page)
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