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Difference Between Glycolysis and Krebs Cycle

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Last updated date: 25th Jul 2024
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The Basics of Metabolism: Glycolysis and the Krebs Cycle

Metabolic pathways are a series of chemical reactions that occur in the cell to convert one molecule into another. These pathways are essential for the maintenance of life, as they allow the cell to break down nutrients and produce energy for cellular processes. There are two main types of metabolic pathways: catabolic pathways and anabolic pathways. Catabolic pathways involve the breakdown of molecules, such as glucose, into smaller components, releasing energy in the process.


Anabolic pathways, on the other hand, involve the synthesis of larger molecules from smaller components, requiring energy in the process. Glycolysis and the Krebs cycle are examples of catabolic pathways, while the synthesis of proteins and nucleic acids are examples of anabolic pathways. The regulation of these pathways is tightly controlled to ensure that the cell has the energy and building blocks it needs to carry out its functions. Now, lets explain glycolysis and krebs cycle.

What is Glycolysis and Krebs Cycle?

Glycolysis 

Glycolysis is the metabolic pathway that converts glucose into pyruvate, producing a small amount of ATP and NADH in the process. It is an anaerobic process, meaning that it takes place in the absence of oxygen, and is the first step of cellular respiration in both prokaryotic and eukaryotic cells. Glycolysis occurs in the cytoplasm of the cell and consists of a series of ten enzyme-catalyzed reactions that break down glucose into two molecules of pyruvate. The process requires the input of two ATP molecules to get started, but ultimately generates four ATP molecules, resulting in a net gain of two ATP molecules. In addition to ATP and NADH, glycolysis also produces two molecules of water and two molecules of ATP.


Krebs Cycle

The Krebs cycle, also known as the citric acid cycle or the tricarboxylic acid (TCA) cycle, is a series of enzyme-catalyzed reactions that occur in the mitochondria of eukaryotic cells and the cytoplasm of prokaryotic cells. The cycle is the second step in cellular respiration and is responsible for generating energy in the form of ATP molecules. The Krebs cycle starts with the breakdown of pyruvate, a three-carbon molecule that is produced during glycolysis, into carbon dioxide, water, and energy.


The cycle then continues with the oxidation of acetyl-CoA, a two-carbon molecule, into carbon dioxide, water, and energy, and ultimately generates a total of two ATP molecules, eight NADH molecules, and two FADH2 molecules per glucose molecule. The NADH and FADH2 molecules are used to generate additional ATP molecules through oxidative phosphorylation in the electron transport chain.


Characteristics of Glycolysis and Krebs Cycle

Glycolysis:

  • Occurs in the cytoplasm of cells.

  • Involves the breakdown of glucose into two molecules of pyruvate.

  • Generates a net gain of two ATP molecules per glucose molecule.

  • Can take place with or without oxygen.

  • Is a relatively fast and efficient process.


Krebs cycle:

  • Occurs in the cytoplasm of prokaryotic cells and the mitochondria of eukaryotic cells.

  • Involves the breakdown of acetyl-CoA into carbon dioxide, water, and energy.

  • Generates a total of two ATP molecules, eight NADH molecules, and two FADH2 molecules per glucose molecule.

  • Requires oxygen.

  • Is a relatively slow and inefficient process.


Glycolysis and Krebs Cycle Difference 

The table presented below highlights the main differences between glycolysis and Krebs cycle.


S.No

Glycolysis

Krebs Cycle

1

Glycolysis occurs in the cytoplasm of cells.

Krebs cycle occurs in the mitochondria of eukaryotic cells and the cytoplasm of prokaryotic cells.

2

Glycolysis begins with one molecule of glucose and ends with two molecules of pyruvate.

Krebs cycle begins with two molecules of acetyl-CoA and ends with carbon dioxide, water, and energy.

3

A net gain of two ATP molecules is generated by glycolysis for each glucose molecule.

Krebs cycle produces a total of two ATP molecules per glucose molecule.

4

Glycolysis is a relatively fast and efficient process.

Krebs cycle is a relatively slow and inefficient process,

5

Glycolysis produces two molecules of NADH.

Krebs cycle produces eight molecules of NADH and two molecules of FADH2.

6

It is a catabolic process.

It is an anabolic process.

7

Glycolysis produces a total of four ATP molecules per glucose molecule.

Krebs cycle produces a total of 36 ATP molecules per glucose molecule.

8

Glycolysis is the first step in cellular respiration and can occur in the absence of oxygen.

Krebs cycle is a central metabolic pathway that requires oxygen and is involved in many other cellular processes.


Summary

Glycolysis and the Krebs cycle are two different metabolic pathways involved in cellular respiration. Glycolysis occurs in the cytoplasm of cells, while the Krebs cycle occurs in the mitochondria of eukaryotic cells and the cytoplasm of prokaryotic cells. Glycolysis begins with one molecule of glucose and ends with two molecules of pyruvate, while the Krebs cycle begins with two molecules of acetyl-CoA and ends with carbon dioxide, water, and energy.


Glycolysis produces a net gain of two ATP molecules per glucose molecule, while the Krebs cycle produces a total of two ATP molecules per glucose molecule. Glycolysis can occur in the presence or absence of oxygen, while the Krebs cycle requires oxygen. Glycolysis is a relatively fast and efficient process, while the Krebs cycle is a relatively slow and inefficient process.

FAQs on Difference Between Glycolysis and Krebs Cycle

1. What is the difference between glycolysis and krebs cycle?

Glycolysis and the Krebs cycle are two different metabolic pathways involved in cellular respiration. Glycolysis occurs in the cytoplasm of cells, while the Krebs cycle occurs in the mitochondria of eukaryotic cells and the cytoplasm of prokaryotic cells. Glycolysis begins with one molecule of glucose and ends with two molecules of pyruvate, while the Krebs cycle begins with two molecules of acetyl-CoA and ends with carbon dioxide, water, and energy. Glycolysis produces a net gain of two ATP molecules per glucose molecule, while the Krebs cycle produces a total of two ATP molecules per glucose molecule. Glycolysis can occur in the presence or absence of oxygen, while the Krebs cycle requires oxygen. Glycolysis is a relatively fast and efficient process, while the Krebs cycle is a relatively slow and inefficient process.

2. What are the end products of glycolysis and how do they differ from the end products of the Krebs cycle?

Glycolysis involves the partial oxidation of glucose, resulting in the production of two pyruvic acid molecules. On the other hand, the Krebs cycle is an aerobic process occurring in the cell's mitochondria, where complete oxidation of the pyruvic acid formed during glycolysis yields carbon dioxide.

3. What are the similarities between glycolysis and krebs cycle?

The similarities between glycolysis and the Krebs cycle are that both metabolic pathways are involved in cellular respiration and energy production. Both pathways involve the breakdown of molecules to produce energy-rich molecules such as ATP. Both glycolysis and the Krebs cycle involve a series of enzyme-catalyzed reactions that are tightly regulated to ensure that the pathways proceed efficiently. Both pathways also involve the production of electron carriers, such as NADH and FADH2, which donate electrons to the electron transport chain to produce ATP. Finally, both pathways are essential for the survival of cells, as they provide the energy necessary for cellular processes such as growth, maintenance, and reproduction.