Helloo world 🙂 For my second video review I chose glycolysis part 1 by BiochemJM. Now going back a little if you all can remember, that my first video review was on carbohydrates the reason behind me picking carbs was for you to get accustom to the molecule of GLUCOSE ! Now if you have not read my review on carbohydrates please do so, and you can also like and comment and all that other good stuff (y)
Since my form 6 days I have never really liked this particular topic because it was so complicated with all these enzymes and long names that I couldn’t even pronounce properly. I used to feel alot like this
But since I have been introduced to the BiochemJM channel on youtube, my hope has been restored. And I gave glycolysis another chance. I really appreciated these videos as it honestly made me understand this topic in literally an hour’s time. I now feel like this
To begin I shall start off with a definition of glycolysis
Basically it is responsible for the production of ATP (adenosine triphosphate) through the degradation of glucose. It does not use molecular oxygen, since it was hypothesized that this mechanism was initiated before earth’s atmosphere contained the element. It occurs in the cytosol of cells.
Here is a little diagram to start us off
Now don’t get sacred, the diagram is alot but it can be broken down.
There are 10 enzymes involved in glycolysis! From the video it was divided into two phases the preparatory phase and the payoff phase.
Dealing with the first phase ( First 5 enzymes of glycolysis)
Reaction 1. Our first priming reaction. ATP dependant phosphorylation of glucose to form glucose 6 – phosphate. It is catalysed by the transferase enzyme hexokinase. It is the first irreversible reaction of glycolysis, because it has a high negative delta G value. The phosphorylation accomplishes two goals : Firstly when hexokinase converts the nonionic glucose into an anion, it becomes trapped in the cell. Why does this happen? Its is because the plasma membrane of the cell does not have transport systems for phosphorylated sugars, so it has no choice but to remain in the cell. Secondly when the phosphate was added it makes the glucose unstable, it is now capable of being further metabolized,
Reaction 2. Involves the relocation of the carbonyl oxygen from carbon 1 to carbon 2. It is an isomerization because the Glucose 6- phosphate (G6P) is converted to fructose 6 – phosphate (F6P). Basically its converting an aldose sugar into a ketose sugar. The enzyme catalyzing this reaction is know as known as phosphohexose isomerase. This is our first reversible reaction.
Reaction 3. Our second priming reaction. Involves the utilization of a second ATP to convert the F6P to fructose 1,6 – bisphosphate. The reason why it is called bisphosphate instead of diphosphate is simple, it is due to the fact that the phosphate groups are not attached to the same carbon atom. This is our second irreversible reaction. The enzyme that catalyzes this reaction is phosphofructokinase -1 or better known as PFK – 1. PFK – 1 is the MOST regulated enzyme in glycolysis.
Reaction 4. The enzyme aldolase would now split the fructose 1,6 – bisphosphate into two 3 carbon products : glyceraldehyde 3-phosphate ( G3P) and dihydroxyacetone phosphate (DHAP) , these two products should seem familiar since they were in my carbohydrates video review :D. So basically we went form a 6 carbon to two 3 carbons.They are also isomers of each other. This is a reversible reaction.
Reaction 5. At this stage one of the previously produced 3 carbon molecules the glyceraldehyde will proceed immediately through glycolysis. However the dihydroxyacetone phosphate will be reconstructed by the enzyme triose phosphate isomerase into another molecule of glyceraldehyde 3-phosphate.
So at the end of the first phase we have two molecules of G3P.
Dealing with the second phase ( last 5 enzymes)
Reaction 6. The enzyme glyceraldehyde 3- phosphate dehydrogenase catalyzes the NAD+ dependant oxidation of G3P to two molecules of 1,3-bisphosphoglycerate and NADH. It the only oxidation reaction in glycolysis, the aldehyde group is being oxidised and forms an acidic group. In this reaction the phosphorylation is not the same as the one that occurred in the the first reaction. The P comes from the 2Pi instead of ATP in the first reaction, and it is the oxidation reaction that provides the energy needed to add the P group to G3P to form 1,3 – bisphosphoglycerate. An important factor to note is that for glycolysis to continue NAD+ must be converted to NADH.
Reaction 7. First ATP forming reaction of glycolysis. A little extra information is that the cell can make ATP in 3 ways and they are :
- substrate level phosphorylation
- by oxidative phosphorylation
Most of the ATP usually comes from the oxidative phosphorylation. In this reaction substrate level phosphorylation occurs, the enzyme phosphoglycerate kinase is used to convert the 1,3 – BPG to form ATP and two molecules of 3- phosphoglycerate.
The remaining reactions of glycolysis are aimed at converting the relatively low energy phosphoacyl- ester of 3PG to a high energy form and harvesting the phosphate as ATP.
Reaction 8. 3PG is converted to 2,3 -bisphosphoglycerate by the enzyme phosphoglycerate mutase, and then the phosphate group on carbon number 3 is removed and you get two molecules of 2- phosphoglycerate.
Reaction 9. The enzyme enolase converts 2PG to two molecules of phosphoenoylpyruvate. In this reaction water is lost and so it is termed a dehydration reaction.
Reaction 10. The final reaction of glycolysis. It is the second ATP forming reaction catalysed by the enzyme pyruvate kinase. And it is the most energetically favorable reaction. In this strongly exergonic reaction the high energy phosphate of PEP is conserved as ATP. The loss of phosphate by PEP leads to the production of two molecules of pyruvate.
This has been the end of my video review on glycolysis I really hope it has helped you, and for more information on this topic you can check out the video itself at :