God Does Not Make Your Body’s Energy. Glycolysis Does.

Image credits belong to: stevepb | Pixabay

Do you ever wonder how a bird gets the potential to fly? The answer is energy. Where does it get the energy? Food molecules are broken down through stages of biochemical reactions. The same energy principle applies to you and me when we do any kind of laborious task. We even use energy while thinking and sleeping. 

Nutrients move into the cell and are metabolized or broken down. A synthesis of molecules occurs, which means different entities are combined to make a new and different whole. They are trafficked around the cell and spread throughout the whole organism.   

Your muscles are constructed from large proteins that are established on smaller molecules built by dietary amino acids. Cellular energy comes from the simple sugars that were once complex carbohydrates. Energy is needed to absorb and metabolize the pathogens, bacteria, and viruses in your body and evacuate toxins and waste materials. All of that requires movement backed by energy.  

Bioenergetics is the general notion explaining the movement of energy through living systems, including cells, that use distinct stages of chemical reactions that build up and break down the complex molecules. Some chemical reactions are spontaneous (i.e., having a course of action uncontrolled by an outside energy force). In contrast, others are non-spontaneous or endergonic, which means that outside energy is supplied. The endergonic reaction's ending amount of energy exceeds its starting amount. Like you and I eat food to restore and recharge ourselves, cells restore and recharge themselves via chemical reactions that expend energy. Metabolism is the totality of chemical reactions occurring within cells, whether done by consumption or generation of energy.  

The sun is the ultimate source of energy for organisms. Plants seize sunlight energy through photosynthesis. Herbivores benefit by eating the plants that have seized that energy. Carnivores benefit by eating the herbivores. The rotting and decay of plants and animals shuttle materials to a nutrient pool.  

Glycolysis: An Important Bioenergetic Process

Glycolysis is a metabolic pathway breaking down glucose (i.e., monosaccharide molecule with six carbon atoms) into three-carbon pyruvate molecules. The purpose is to gather energy from glucose. Glycolysis evolved long, long ago (see more on this below). It is the initial stage of cellular respiration in our bodies. However, it is also present in many anaerobic (i.e., not requiring oxygen) organisms. Glycolysis occurs within the cytosol (liquid parts) of the cell. The energy-requiring phase rearranges glucose molecules and attaches phosphates groups to them. A modified, unstable sugar called fructose-1,6-bisphosphate is the result. 

There are ten steps to glycolysis:

Step 1: Hexokinase is the enzyme that gets the whole ball rolling. It transforms D-glucose into glucose-6-phosphate. Phosphorylation takes place, which means that phosphate groups are taken from adenosine triphosphate (ATP) molecules and added to the glucose ring. 

Step 2: Phosphoglucose isomerase is the enzyme that swaps around the parts of glucose-6-phosphate to then make fructose 6-phosphate. Isomers, which have identical molecular formulas but different atomic arrangements, are involved at this point. 

Step 3: Fructose 6-phosphate now wants to change. It wants to become fructose 1,6-bisphosphate. Phosphofructokinase makes the conversion happen by using a second ATP molecule to add a phosphate group onto the F6P molecule. 

Step 4: Aldolase is the enzyme that divides fructose 1, 6-bisphosphate into 3-carbon sugars with isomers (rearranged parts) called dihydroxyacetone phosphate (DHAP) and glyceraldehyde 3-phosphate (GAP). 

Step 5: Triosephosphate isomerase is the enzyme that transforms the dihydroxyacetone phosphate (DHAP) and glyceraldehyde 3-phosphate (GAP) molecules. Glyceraldehyde phosphate is excluded and used as a substrate for the next glycolytic stage.

Step 6: Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is the next breathtakingly long name for the enzyme that removes a hydrogen atom from GAP and transfers it to nicotinamide adenine dinucleotide (NAD+). GAPDH takes a phosphate from the cell's cytosol and adds it to the oxidized GAP, which then generates 1,3-bisphosphoglycerate (BGP). Both GAP molecules of the prior stage are dehydrogenated and phosphorylated. 

Step 7: Phosphoglycerate kinase is the next enzyme on the scene. It takes a phosphate group from 1,3-bisphosphoglycerate (BGP) and moves it to adenosine diphosphate (ADP) to form adenosine triphosphate (ATP) and 3-phosphoglycerate. This ATP synthesis will exhaust the two ATP molecules used earlier and leave us with zero ATP molecules. 

Step 8: Phosphoglyceromutase is the next enzyme to cause a rearrangement of phosphate positions. It generates a 2-phosphoglycerate by swapping the phosphates of the third and second carbons. 

Step 9: Enolase is the enzyme that removes a water molecule from 2-phosphoglycerate to make phosphoenolpyruvic acid (PEP).

Step 10: This is the final step in which pyruvate kinase transforms phosphoenolpyruvate into pyruvate by taking a phosphate group belonging to the 2' carbon of the PEP and moving it to an ADP molecule to generate ATP. 

I found a paper apparently from 1993 discussing the evolution of glycolysis:

3-phosphoglycerate kinases (PGK) were studied in methane-producing microorganisms under anaerobic conditions. These kinases were found to be 30-36% exactly like other eukarya, therefore, indicating they share a common ancestor. However, homology was found lacking among GAPDHs, indicating that archaeal GAPDHs did not descend from the same protein that gave rise to the bacterial/eukaryal GAPDHs. 

"It is, therefore, possible that glycolysis arose as an association of enzymes which worked on substrates of similar structure. Some of the enzymes therefore share common ancestors and some of which are descended from different 'parent' molecules."

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