LESSON 1: GLYCOLYSIS
INTRODUCTION
Alright, so we all know that our bodies go through cellular respiration in order to generate the energy we need to function. You have previously learned the simple reaction our bodies go through to produce energy.This energy largely comes from ATP molecules, or adenosine triphosphates, which are produced directly and indirectly through a variety of chronological processes in our bodies. Producing this energy in the form of ATP requires much more complex equation and a plethora of reactions and processes.The first of these processes is called glycolysis.
PART 1: Glucose Activation
In glycolysis the opening act, or "Act I" as Shakespeare would say, is called Glucose Activation. Now you've all already learned in simple words that glucose, a type of sugar, is primarily what we consume in order to absorb the energy we need to move around, do things, get active, et cetera.Thus, a molecule of a glucose, made up of 6 carbons, enters the cytoplasm of any given cell in the body. The first reaction this molecule goes through is called phosphorylation. In this reaction, an enzyme helps in breaking down a pre-existing ATP molecule into its 2 parts, adenosine diphosphate (ADP) and a high energy phosphate group (Pi). This breakdown releases enough energy for the phosphate to be added onto the glucose molecule and we get glucose-6-phosphate, the 6 indicating which carbon the phosphate has attached or bonded to.
Phosphorylation can be seen as the spending of money; to get the phosphate you need you have to pay the cost, which comes in the currency of ATP. After this, another enzyme helps in rearranging the atoms of the glucose-6-phosphate to form fructose-6-phosphate. To end off Act I, another 1 ATP is invested to "buy" a phosphate and attach it to the molecule, finally forming fructose-1,6-bisphosphate. Cue the applause, that concludes Act I of Glycolysis!
PART 2: SUGAR SPLITTING
In Act II, one of the shortest acts, we are introduced to 2 new characters. The fructose-1,6-bisphosphate molecule is split into dihydroxyacetonephosphate (DHAP) and glyceraldehyde-3-phosphate (G3P). Now, trying to keep track of 2 differently named characters makes us as the audience quite confused so for simplicity the DHAP is converted into G3P, producing 2 G3P molecules at the end of the Sugar Splitting stage. Keep in mind that each of these steps and reactions are all catalyzed, or "sped" up, by a specific enzyme. Since there are now 2 G3P, all of the following reactions happen twice.
PART 3: OXIDATION
Next is Act III. At this point, each of the G3P molecules need to get another phosphate. However, there is no access to more money in the form of ATP, so we must deal in another currency. Thus, the G3P goes through oxidation. In oxidation, each of the G3P molecules lose one hydrogen atom and add it on to an NAD+ molecule, forming 2 NADH. This reaction produces the energy required to attach a pre-existing phosphate group onto the molecule. We now have 1,3-bisphosphoglycerate (BPG). If this oxidation confuses you, think of it as another form of "paying up" to get what you need, but this time, the currency is in H. When you pay the bank (let's call the bank NAD+ - National Administration of Dealing) your 1 H, they can now be called the National Administration of Dealing Hydrogen (NADH! See how it works?). The bank then gives you a store credit (energy) and you're off to buy your phosphate group.
PART 4: FORMATION OF ATP
The final act of glycolysis is known as the Formation of ATP, arguably the most important stage of the process. In this part of glycolysis, the initial investment in Act I (Glucose Activation) finally comes to a profit. For each of the BPGs, 1 phosphate molecule is removed and attached to an ADP molecule, forming 2 ATP through the process of substrate level phosphorylation!
A good way to think about it is as a return on the investment made in the beginning; the glucose and fructose-6-phosphate molecules from early on both had to pay 1 ATP each (2 ATP total) to buy the phosphates they needed. Now, since both of the BPGs are "returning" 2 phosphates to 2 ADP, they get their "money" back in the form of 2 ATP. You may say at this point that the molecules have "broken even". The result of this transaction is two 3-phosphoglycerates (3PG).
Using another one of the unique enzymes, both of the 3PGs are rearranged to form two 2-phosphoglycerates (2PG). Next, the 2PGs go through another rearrangement and this time 1 water molecule, or H2O, is released from each of the 2PGs producing 2 H2O as waste products. If you have trouble remembering this, just remember that 2PGs are very hard working molecules and when they rearrange themselves, they "sweat" off "water". The resultant molecules of this step are referred to as phosphoenolpyruvate (PEP). In the last and final reaction, the PEPs have another "return on their investment" and go through substrate level phosphorylation again. Each of the PEPs remove 1 phosphate molecule and attach it to an ADP, forming 2 ATP yet again. Now not only have the molecules broken even, they have also made a profit of 2 ATP molecules.
The final products formed after this reaction are the 2 pyruvates, each made of 3 carbons (recall the sugar splitting step in which the 6 carbons of glucose were split in half). Pull the curtains and take a bow!
A good way to think about it is as a return on the investment made in the beginning; the glucose and fructose-6-phosphate molecules from early on both had to pay 1 ATP each (2 ATP total) to buy the phosphates they needed. Now, since both of the BPGs are "returning" 2 phosphates to 2 ADP, they get their "money" back in the form of 2 ATP. You may say at this point that the molecules have "broken even". The result of this transaction is two 3-phosphoglycerates (3PG).
Using another one of the unique enzymes, both of the 3PGs are rearranged to form two 2-phosphoglycerates (2PG). Next, the 2PGs go through another rearrangement and this time 1 water molecule, or H2O, is released from each of the 2PGs producing 2 H2O as waste products. If you have trouble remembering this, just remember that 2PGs are very hard working molecules and when they rearrange themselves, they "sweat" off "water". The resultant molecules of this step are referred to as phosphoenolpyruvate (PEP). In the last and final reaction, the PEPs have another "return on their investment" and go through substrate level phosphorylation again. Each of the PEPs remove 1 phosphate molecule and attach it to an ADP, forming 2 ATP yet again. Now not only have the molecules broken even, they have also made a profit of 2 ATP molecules.
The final products formed after this reaction are the 2 pyruvates, each made of 3 carbons (recall the sugar splitting step in which the 6 carbons of glucose were split in half). Pull the curtains and take a bow!
The final products formed after this reaction are the 2 pyruvates, each made of 3 carbons (recall the sugar splitting step in which the 6 carbons of glucose were split in half). Pull the curtains and take a bow!
OVERVIEW
To understand the main purpose of glycolysis, think of it as a gumball machine. For each glucose molecule we know that 2 pyruvates are being produced. This is much like when you insert a quarter into a gumball machine and get 2 gumballs. In this case, the glucose molecule would serve as the quarter and the 2 gumballs that you get from this investment would be the 2 pyruvate molecules. The same way that there are extra candy pieces or different sweets that come out of the machine sometimes, glycolysis also produces 2 H2O, 2 NADH, and 2 ATP along with the 2 pyruvates. Here's the overall net reaction of glycolysis that should help you when studying: