The key difference between the glycolysis krebs cycle and electron transport chain is the net yield. Glycolysis produces two pyruvates, two ATP, and two NADH, while Krebs cycle produces two carbon dioxide, three NADH, one FADH2, and one ATP. Electron transport chain, on the other hand, produces thirty-four ATP and one water molecule.
Cellular respiration is a series of metabolic reactions that occur in the cells of organisms to convert chemical energy from oxygen or nutrients into ATP and release waste products. It typically involves nutrients like carbohydrates, fatty acids, and proteins. The most common oxidizing agent providing chemical energy is molecular oxygen. This chemical energy stored in ATP drives processes that require energy, such as biosynthesis, locomotion, or the transportation of molecules across cell membranes. Cellular respiration is one of the ways where a cell releases chemical energy to fuel cellular activities. These reactions take place in a series of biochemical pathways. Glycolysis, Krebs cycle, and electron transport chain, which are redox reactions, are these pathways.
CONTENTS
1. Overview and Key Difference
2. What is Glycolysis
3. What is Krebs Cycle
4. What is Electron Transport Chain
4. Similarities – Glycolysis Krebs Cycle and Electron Transport Chain
5. Glycolysis vs Krebs Cycle vs Electron Transport Chain in Tabular Form
6. Summary – Glycolysis vs Krebs Cycle vs Electron Transport Chain
What is Glycolysis?
Glycolysis is a metabolic pathway that converts glucose into pyruvate. This process takes place in the cytoplasm. It is the first step in the breakdown of glucose to extract energy in the process of cellular metabolism. Glycolysis is also known as the first step in cellular respiration. Glycolysis consists of a series of reactions to extract energy, which includes splitting of the six-carbon molecule; glucose to three-carbon molecules; pyruvates. During this process, the free energy released is used to produce high-energy molecules such as adenosine triphosphate (ATP) and nicotinamide adenine dinucleotide (NADH).
Figure 01: Glycolysis
Glycolysis pathway consists of ten reactions catalyzed by ten different enzymes. This metabolic pathway does not require oxygen, so it is considered an anaerobic pathway. Glycolysis pathway has two separate phases: preparatory phase, where ATP is consumed, and pay off phase, where ATP is produced. Each phase consists of five steps. During the preparatory phase, the first five steps take place – they consume energy to convert glucose to three-carbon sugar phosphates. Pay off phase involves the last five steps where there is a net gain of energy-rich molecules. Since glucose leads to two triose sugars during the preparatory phase, each reaction in pay off phase occurs twice per glucose molecule. Therefore, there is a yield of two NADH molecules and four ATP molecules. The net gain of glycolysis includes two pyruvate molecules, two NADH molecules, and two ATP molecules.
What is Krebs Cycle?
Krebs cycle (citric acid cycle or tricarboxylic acid cycle) is a series of chemical reactions to release stored energy through the oxidation of acetyl co-A, two-carbon acetyl group which is derived from carbohydrates, proteins, and fats. Pyruvate, which is produced during glycolysis, converts into acetyl co-A.
Figure 02: Krebs Cycle
Krebs cycle takes place in the matrix of mitochondria of eukaryotes and in the cytoplasm of prokaryotes. This cycle is a closed-loop pathway that includes eight steps. Here, the last part of the pathway reforms the four-carbon molecule, oxaloacetate, which is used in the first step. In this metabolic pathway, citric acid that is consumed is regenerated in a sequence of reactions to complete the cycle. Krebs cycle initially consumes acetyl co-A and water, reducing nicotinamide adenine dinucleotide (NAD+) to NADH. As a result, carbon dioxide is produced. Krebs cycle finally produces two carbon dioxide molecules, one GTP or ATP, three NADH molecules, and one FADH2. The eight steps of this cycle series involve redox, dehydration, hydration, and decarboxylation reactions. Krebs cycle is considered an aerobic pathway since oxygen is used.
What is Electron Transport Chain?
The electron transport chain (ETC) is a pathway that consists of series of protein complexes that transfer electrons from electron donors to electron acceptors through redox reactions. This causes hydrogen ions to accumulate within the matrix of mitochondria. ETC takes place within the inner membrane of the mitochondria. Here, a concentration gradient is formed where hydrogen ions diffuse out of the matrix by passing through the ATP synthase enzyme. This phosphorylates ADP producing ATP.
Figure 03: Electron Transport Chain
ETC is the last step of aerobic respiration where electrons are passed from one complex to another, reducing molecular oxygen to produce water. There are four protein complexes involved in this pathway. They are labelled as complex I, complex II, complex III, and complex IV. The unique feature of the ETC is the presence of a proton pump to create a proton gradient across the mitochondrial membrane. In other words, electrons are shuttled from NADH and FADH2 to molecular oxygen. Here, protons are pumped from the matrix to the inner membrane of mitochondria, and oxygen is reduced to form water. The net gain of the ETC includes thirty-four ATP molecules and one water molecule.
What are the Similarities Between Glycolysis Krebs Cycle and Electron Transport Chain?
- Glycolysis, Krebs cycle, and electron transport chain are three steps involved in cellular respiration.
- All three pathways are enzyme-mediated.
- These pathways produce ATP.
- The Krebs cycle and ETC are aerobic pathways.
- Glycolysis and Krebs cycle produce NADH.
- Both Krebs cycle and ETC take place in the mitochondria.
What is the Difference Between Glycolysis Krebs Cycle and Electron Transport Chain?
Glycolysis produces two pyruvates, two ATP, and two NADH, while Krebs cycle produces two carbon dioxide, three NADH, one FADH2, and one ATP. Electron transport chain produces thirty-four ATP and one water molecule. This is the key difference between glycolysis Krebs cycle and electron transport chain. Glycolysis consists of ten steps that involve ten different enzymes and is a linear sequence, while Krebs cycle consists of eight steps, and it is a closed-loop pathway where the last part of the pathway reforms the molecule that is used in the first step. On the other hand, electron transport chain is a series of reactions that consist of four protein complexes and is also a linear sequence. This is another difference between glycolysis krebs cycle and electron transport chain. Moreover, glycolysis consumes ATP while Krebs cycle and electron transport chain does not consume ATP. Another difference between glycolysis krebs cycle and electron transport chain is that glycolysis is an anaerobic pathway while Krebs cycle and ETC are aerobic pathways.
The following infographic lists the differences between glycolysis krebs cycle and electron transport chain in tabular form.
Summary – Glycolysis vs Krebs Cycle vs Electron Transport Chain
Cellular respiration is one of the ways where a cell releases chemical energy to fuel needed for cellular activities. This includes three biochemical pathways: Glycolysis, Krebs cycle, and Electron transport chain. Glycolysis is a metabolic pathway that converts glucose into pyruvate. This is an anaerobic pathway that takes place in the cytoplasm. Glycolysis is also known as the first step in cellular respiration. Glycolysis pathway consists of ten reactions catalyzed by ten different enzymes. Krebs cycle is a series of chemical reactions to release stored energy through the oxidation of acetyl co-A, two-carbon acetyl group. Krebs cycle takes place in the matrix of mitochondria. It is a closed-loop pathway that includes eight steps. Krebs cycle is the second step of cellular respiration and is an aerobic pathway. The electron transport chain is a pathway that consists of series of protein complexes that transfer electrons from electron donors to electron acceptors through redox reactions. It is also an aerobic pathway that takes place within the inner membrane of the mitochondria. Thus, this summarizes the difference between glycolysis krebs cycle and electron transport chain.
Reference:
1. Aryal, S., Nouran, Nkem, I., Jade, K, J., Worm, B., Jhorar, R. “Glycolysis explained in 10 easy steps (with diagrams)” Microbiologyinfo.
2. “The Citric Acid (Krebs) Cycle” Boundless microbiology.
Image Courtesy:
1. “Glycolysis including irreversible steps” By Lkate2014 – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Citric acid cycle with aconitate 2” By Narayanese, WikiUserPedia, YassineMrabet, TotoBaggins – Image adapted from Image: Citric acid cycle noi.svg (CC BY-SA 3.0) via Commons Wikimedia
3. “2508 The Electron Transport Chain” By OpenStax College – Connexions Web site. Jun 19, 2013. (CC BY 3.0) via Commons Wikimedia