Now, the Citric Acid Cycle is also known as the Krebs Cycle or the TCA Cycle, and it's a central stage in energy generation from food. Here, it oxidizes the Acetyl group of Acetyl CoA. This represents our Acetyl CoA. When we say the Acetyl group, it is this portion that is in orange. And it does this to produce high energy molecules such as ATP, NADH, and FADH2. We're talking about this. Now remember, we say that this is broken down into 4 stages. We have our proteins, carbohydrates, and lipids undergoing digestion in the first stage, and they are broken down into amino acids, monosaccharides, and fatty acids in the second stage. We then form our Acetyl CoA, which then goes into our Citric Acid Cycle or Krebs Cycle for stage 3 to create NADH and FADH2. Now the NADH and FADH2 are utilized in the ETC or electronic transport chain to produce energy required for ATP synthesis. So remember, in stage 3, these are generated and they go directly into the electron transport food catabolism. And now we're going to pay a little bit more attention to the food catabolism and the Krebs Cycle or Citric Acid Cycle.
Intro to Citric Acid Cycle - Video Tutorials & Practice Problems
Intro to Citric Acid Cycle Concept 1
Video transcript
Intro to Citric Acid Cycle Example 1
Video transcript
Which of the following statements about the citric acid cycle is incorrect? The carbon dioxide produced from the citric acid cycle is a product of oxidation. That is true. Remember, we have Acetyl CoA going into the citric acid cycle. We make NADH, FADH2, but we also create energy and carbon dioxide by oxidation. The citric acid cycle oxidizes the Acetyl group of the Acetyl CoA to produce energy. This is true. Oxidation reactions in the Citric Acid Cycle produce coenzymes NAD+ and FAD. This is not true. We oxidize our Acetyl CoA in order to reduce these two to create NADH plus FADH2. So this is incorrect. Then finally, the Citric Acid Cycle is part of the common metabolic pathway. Remember, the common metabolic pathway is stages 3 and stage 4 of our food catabolism. The Citric acid being part of stage 3 means that it is part of the common metabolic pathway. So this is true. Right? So here, the only statement that is incorrect would be option C.
Phases of the Citric Acid Cycle Concept 2
Video transcript
Now, the citric acid cycle consists of multiple steps which can be grouped into three phases. Now, here we're going to say the first phase is our citrate formation. Here, the Acetyl group from the Acetyl CoA, so we're starting with Acetyl CoA here, reacts with our Oxaloacetate, so reacts with this, in order to form our citrate. This is a cyclic metabolic pathway, so this here is interacting with what's coming into the citric acid cycle in the form of Acetyl CoA. The second phase deals with Succinyl CoA formation. Here, we have the isomerization and oxidation reactions that convert our citrate into succinyl CoA. Here's succinyl CoA. As a result of this, in this stage, we have also the production of NADH+CO2. Going into the third stage, we have oxaloacetate regeneration. Here, we are going to say we have the hydrolysis and oxidation reactions convert our succinyl CoA back into oxaloacetate. Basically, we're going from Acetyl CoA and going towards Oxaloacetate. As a result of this, we're also creating NADH, FADH2, and some ATP in the form of energy. Remember, this NADH and FADH2, later on, will go into the electron transport chain to create even more energy in the form of ATP.
Phases of the Citric Acid Cycle Example 2
Video transcript
Identify each of the following statements about the citric acid cycle as true or false. So for a, it says, Phase C of the Citric Acid Cycle includes reactions that regenerate oxaloacetate. That is true because then it reacts with acetyl CoA at the beginning of the citric acid cycle to create citrate. Which leads us to the next statement. The first phase of the citric acid cycle, yes, uses acetyl CoA and oxaloacetate to produce citrate. This is true. The Citric Acid cycle relies on reduction reactions to produce high-energy molecules. That is not true. It relies on oxidation reactions to produce high-energy molecules in the form of NADH plus FADH2. And then finally, oxidation reactions in phase C produce CO2. Now in phase C, we're producing NADH, FADH2, as well as ATP. So this would be false. Alright. So this is how we could describe each of the statements within this given example question.
Which one of the following substances is a part of both phases A and C of the citric acid cycle?
Succinyl CoA
Oxaloacetate
Acetyl CoA
Citrate