BIOC 212 Lecture Notes - Lecture 50: Glycogen Phosphorylase, Glucagon, Glycogen Synthase

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Metabolism XII
Mitochondria Generate ATP from NADH Oxidation
Mitochondria are specialized organelles that have evolved to generate the
electrochemical gradient across the inner membrane by the activity of the
enzymes that oxidize NADH and FADH2 back to NAD+ and FAD
o Double membrane
o Impermeability of inner membrane is important as it is the energetic
reservoir step before production of ATP
o Most of energy produced in glycolysis in mammalian cells is ultimately
stored as this electrochemical gradient
This is why have so many complex mechanisms for getting metabolites
& proteins across the inner membrane
Evolutionary requirement for maintaining permeability is so critical for
energetic properties of the cell
The electrochemical gradient is the ultimate carrier for the chemical energy
released by glucose and fatty acid oxidation before ATP production
This is why inner membrane impermeability is so important
o Gradient formed is used to make ATP
Excess Glucose Stored in Polysaccharides
Cells in the body are not always in a state of needing more energy
o Frequently, cells will be able to take up glucose and not actually need it to
generate ATP, own metabolic proteins or lipid substrates at the moment
Glucose molecules are linked to form glycogen (animals) or starch (plants)
o All organisms have evolved ways to store energy when not needed
o In mammals, glucose mostly stored in the form of glycogen
When liver cells or muscle cells are able to take up glucose from the
bloodstream but do not need it immediately for their own metabolic
requirements or for export
Funnel it off of the glycolytic pathway after step 1 as glucose-6-P
Glucose-6-phosphate (product of step 1 in glycolysis) can be redirected to be
stored in cells with sufficient ATP levels
o Glucose-6-P is then incorporated into a growing glycogen chain
Stored there ready to go for whenever the cell needs it
Upon local starvation of the cell or upon signaling from extracellular cues that
tell the cells to release glucose to the bloodstream
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