~Overview of Glycolysis and description of the pathway
~Divergence to anaerobic metabolism within the muscle and how does aerobic metabolism also help energize our muscles?
~The three main energy sources for our muscles.

~Ancient metabolic pathway used by the earliest bacteria
~This pathway existed about 1 million years before oxygen existed on the earths surface.
~Basically, glycolysis is a set of chemical reactions that produce energy (in the form of ATP) from the sugar glucose.
~In the 10 steps of glycolysis glucose is converted to pyruvate and the reaction yeilds 2 pyruvate molecules and 2 net ATP molecules per glucose.

Anaerobic glycolysis is the process by which the normal pathway of glycolysis is routed to produce lactate. It occurs at times when energy is required in the absence of oxygen. It is vital for tissues with high energy requirements, insufficient oxygen supply or absence of oxidative enzymes.
Glycolysis produces reduced forms of NAD in the energy generation phase.
In an anaerobic environment, lactate dehydrogenase converts pyruvate to L-lactate and restores NADH to NAD+ which can then be used in once again in the glycolysis pathway.

Pyruvate + NAD + + CoA Acetyl CoA + CO
2
+ NADH + H +
Using pyruvate in this way (to keep glycolysis running at a paltry
2ATP per glucose) may seem wasteful considering the much larger amount of ATP generated should it enter the citric acid cycle (as acetyl CoA). However, glycolysis can run at a very high rate and thus meet the ATP demands of the cell (at least for a short time) even though it is a very expensive use of glucose.
But… a continuous buildup of lactic acid could lead to acidosis

It turns out breakdown of glucose to pyruvate within muscle cells is not the primary source of ATP synthesis .
ATP is the immediate source of energy for muscle contraction. Although a muscle fiber contains only enough ATP to power a few twitches, its
ATP "pool" is replenished as needed. There are three sources of high-energy phosphate to keep the ATP pool filled.
• creatine phosphate
• glycogen
• cellular respiration in the mitochondria of the fibers.

Creatine phosphate and cellular respiration as a source of ATP for the muscle
The phosphate group in creatine phosphate is attached by a "highenergy" bond like that in ATP.
Creatine phosphate + ADP ↔ creatine + ATP
Aerobic production of ATP aids in the reproduction of glycogen from the lactic acid that has built up within the muscle.

Biochemistry second edition written by Christopher Mathews and
K.E. Van Holde.
Pictures from:
• http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/M/Muscles.html
• http://www.umanitoba.ca/faculties/medicine/units/biochem/coursenotes/blanchaer_ tutorials/Bob/metabolism
• http://www.arabidopsis.org:1555/ARA/new-image?type=PATHWAY&object=
• ANAGLYCOLYSIS-PWY