Citric Acid Cycle Steps Simplified
The citric acid cycle, or Krebs cycle doesn’t have to be as scary as it may appear to be. Here, you’ll see the citric acid cycle steps simplified in an easy to understand way that will help you to have a much better grasp on how this metabolic pathway works together with many other pathways in the body such as glycolysis, the glucose alanine cycle, beta oxidation, and many more. In this article I will break down all of the citric acid cycle steps simplified in 10 easy to understand steps that will help you to have a much better grasp on the entire process as a whole.
Step 1 citric acid cycle steps simplified
The first step of the citric acid cycle starts with pyruvate. Pyruvate is the product of the metabolic pathway known as glycolysis (as well as glycogenolysis). Pyruvate results after the compete breakdown of a gluose/glycogen molecule. Once a glucose/glycogen molecule is broken down into a pyruvate molecule, the pyruvate is then converted into Acetyl-CoA.
Step 2 citric acid cycle steps simplified
Step 2 is a very important step as Acetyl-CoA will then “enter” or “begin” the citric acid cycle by combining with Oxaloacetate to form Citrate (citric acid). This can be thought of as the beginning of the citric acid cycle and the first of many other conversions that will occur in this metabolic pathway.
Step 3 citric acid cycle steps simplified
Once Citrate is created via the combination of Acetyl-CoA and Oxaloacetate, the cycle then continues by having Citrate form into Isocitrate. Nothing really significant happens from the conversion of Citrate to Isocitrate. There is no NADH or FADH formed as a result of this conversion.
Step 4 citric acid cycle steps simplified
Isocitrate then converts into Alpha-Ketoglutarate. During the transition of conversion, a CO2 molecule is released. Also, a NAD molecule is converted into NADH. These NADH’s, as well as the FADH’s that will be created in the citric acid cycle will eventually make their way to the electron transport chain to create ATP for energy.
Step 5 citric acid cycle steps simplified
Once Alpha-Ketoglutarate is created, it is then converted into Succinyl-CoA. This is considered about the halfway mark of the citric acid cycle. When Alpha-Ketoglutarate transitions to Succinyl-CoA, another CO2 molecule is released. Also, another NAD is converted into NADH to be brought over to the electron transport chain.
Step 6 citric acid cycle steps simplified
Succinyl-CoA then gets converted into Succinate. When this happens, GDP+Pi is then converted into GTP. In this step, a molecule of guanosine triphosphate (GTP) is synthesized. GTP is a molecule that is very similar to ATP in its energetic properties and structure and can be used in cells in an analogous way .
Step 7 citric acid cycle steps simplified
Succinate then gets converted into Fumarate. When this happens, a FAD molecule gets converted into FADH. FADH, or flavin adenine dinucleotide is a prosthetic group of a protein that is involved in several important enzymatic reactions, such as with the citric acid cycle of course. The FADH created from the conversion of Succinate to Fumarate will get transferred to the electron transport chain.
Step 8 citric acid cycle steps simplified
Femurate then gets converted into Malate without the creation of any NADH or FADH. Also, there is no CO2 released as a result of this reaction either. Now we are getting into the homestretch of this metabolic pathway. This will become evident as we get into step 9 of the citric acid cycle.
Step 9 citric acid cycle steps simplified
What happens here is Malate gets converted back into Oxaloacetate. Remember, Oxaloacetate was one of the first molecules that we used in the citric acid cycle. From the conversion of Malate to Oxaloacetate, a NADH molecule gets converted from NAD. As stated before, NADH is then transferred into the electron transport chain to be used to create ATP that the body can use to perform work.
Step 10 citric acid cycle steps simplified
The 10th and final step of the citric acid cycle is when Oxaloacetate combines with the Acetyl-CoA that was initially made after being converted from pyruvate, and then creates citric acid. The cycle then repeats itself over and over again.
As you can clearly see throughout these 10 steps, the citric acid cycle is just that, a cycle. The cycle turns and turns as NADH’s and FADH’s get created from select conversions. These molecules will then get transferred to the electron transport chain to then eventually get converted into ATP. ATP is one of the main end goals here. The citric acid cycle is an extremely powerful metabolic pathway that is very efficient at yielding molecules with the energy potential to perform work in the real world.
Hopefully what you’ve seen here with these citric acid cycle steps simplified has done just that and made it much easier for you to understand not only how this cycle works, but also how it works in harmony with the metabolic pathways that work alongside it.
Citric Acid Cycle Steps Simplified (Visual)
- “The Citric Acid Cycle.” Spark Notes. http://www.sparknotes.com/biology/cellrespiration/citricacidcycle/section2.rhtml