14 Difference Between Glycolysis And Kreb’s Cycle (With Diagram)

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What Is Glycolysis?

Glycolysis also referred to as cytoplasmic pathway, takes place in the cytosol of the cell’s cytoplasm and is the first step in breakdown of glucose (C6H12O6) to extract energy for cellular metabolism to produce energy in the form of ATP. Through two distinct phases, the six-carbon ring of glucose is split into two three-carbon sugar molecules referred to as pyruvates (CH3COCOO) in a series of enzymatic reactions. The second phase of Glycolysis completes conversion of pyruvate and produces two molecules of ATP, two molecules of NADH and two molecules of water. NADH and ATP are eventually utilized by cells for energy.

Glycolysis can occur with or without oxygen. In the presence of oxygen, Glycolysis becomes the first stage of cellular respiration. In the absence of oxygen, Glycolysis allows cells to make small amounts of ATP through a process of fermentation. It is also important to note, that Glycolysis is a sequence of ten enzyme-catalyzed reactions.

Glycolysis Pathway

 What You Need To Know About Glycolysis Cycle/Cytoplasmic Pathway

  1. Glycolysis is the first stage of cellular respiration.
  2. Glycolysis is concerned with carbohydrate metabolism.
  3. In Glycosis a molecule of glucose is degraded into two molecules of an organic substance, pyruvate.
  4. Glycolysis is a chain straight or linear pathway.
  5. No Carbon dioxide is evolved in Glycolysis.
  6. Glycolysis occurs inside the cytoplasm.
  7. Glycolysis consumes two ATP molecules for the initial phosphorylation of substrate molecule.
  8. In Glycosis, net gain is two molecules of NADH and two molecules of ATP for every molecule of glucose broken down.
  9. The process is not connected with oxidative phosphorylation.
  10. In Glycolysis, one glucose molecule liberates 4 ATP molecules through substrate level phosphorylation.
  11. Oxygen is not a requirement for Glycolysis.
  12. The net gain of energy is equal to 8 ATP.
  13. The process occurs in both aerobic and anaerobic respiration.
  14. Glycolysis has different enzymes as phosphohexo isomerase, Hexokinase, Aldolase, Dehydroganase, Kinase, Mutase and Enolase.

Also Read: Difference Between Cellular Respiration And Photosynthesis

What Is Kreb’s Cycle?

Kreb’s Cycle

Kreb’s cycle also referred to as citric acid cycle or TCA (tricarboxylic acid cycle) is a series of chemical reactions used by all aerobic organisms to release stored energy through the oxidation of acetyl-CoA derived from carbohydrates, fats and proteins into adenosine triphosphate (ATP) and carbon dioxide. In addition, the cycle provides precursors of certain amino acids as well as the reducing agent NADH that are used in other numerous reactions.

The kreb’s cycle uses the two molecules of pyruvic acid formed in Glycolysis and yields high-energy molecules of NADH and flavin adenine dinucleotide (FADH2), as well as some ATP. Before getting into kreb’s cycle, the pyruvic acid molecules undergo some changes. Each of the three-carbon pyruvic acid molecules undergo conversion to a substance referred to as acetyl-coenzyme A or acetyl-CoA.  In the process, the pyruvic acid molecule is broken down by an enzyme, one carbon atom is released in the form of carbon dioxide and the remaining two carbon atoms are combined with a coenzyme referred to as coenzyme A. This combination forms acetyl-CoA. In the process, electrons and a hydrogen ion are transferred to NAD to form high-energy NADH.

In the presence of oxygen, organisms are capable of using the Kreb’s cycle. This is because oxygen is required to oxidized NADH and FADH2 produced in the kreb’s cycle, in the electron transport chain (ETC) thus replenishing  the supply of NAD+ and FAD.

At the end of the tricarboxylic acid cycle, the final product is oxaloacetic acid. This is similar to oxaloacetic acid that began the cycle; therefore the molecule is very much ready to accept another acetyl-CoA molecule to commence another turn of the cycle.

What You Need To Know About Kreb’s Cycle/Tricarboxylic Cycle

  1. Kreb’s cycle is the second stage of cellular respiration.
  2. Kreb’s cycle is the primary cycle for oxidation of carbohydrate, lipid and proteins.
  3. In Kreb’s cycle, pyruvate is completely degraded into inorganic substances such as carbon dioxide (CO2) and water (H2O).
  4. Kreb’s cycle is a cyclic pathway.
  5. Carbon dioxide is evolved in Kreb’s cycle.
  6. Kreb’s cycle occurs inside the mitochondria.
  7. It does not consume ATP.
  8. Kreb’s cycle produces 6 molecules of NADH and 2 molecules of FADH2 for every two molecules of Acetyl CoA oxidized by it. Two molecules of NADH are liberated during conversion of two pyruvates to Acetyl CoA.
  9. Kreb’s cycle is connected with oxidative phosphorylation.
  10. In Kreb’s cycle, two acetyl residues liberate two ATP or GTP molecules through substrate level phosphorylation.
  11. Kreb’s cycle uses oxygen as terminal oxidant.
  12. In Kreb’s, the net gain of energy is equal to 24 molecules of ATP. Six molecules of ATP can be produced from 2NADH2 formed during dehydrogenation of two pyruvates.
  13. Kreb’s cycle only occurs in aerobic respiration.
  14. Kreb’s cycle has different enzymes such as Aconitase, Isocitrate dehydroganase, alpha-ketoglutarate denhydroganase, Succinyl synthase, Fumarase and Malic dehydroganase.

Also Read: Difference Between Aerobic And Anaerobic Respiration

Difference Between Glycolysis And Kreb’s Cycle In Tabular Form

BASIS OF COMPARISON GLYCOLYSIS KREB’S CYCLE
Description Glycolysis is the first stage of cellular respiration.   Kreb’s cycle is the second stage of cellular respiration.  
Primary Role Glycolysis is concerned with carbohydrate metabolism.   Kreb’s cycle is the primary cycle for oxidation of carbohydrate, lipid and proteins.  
Type Of Pathway It is a chain straight or linear pathway.   It is a cyclic pathway.  
End Products Of Degradation In this process a molecule of glucose is degraded into two molecules of an organic substance, pyruvate.   In this cycle, pyruvate is completely degraded into inorganic substances such as carbon dioxide (CO2) and water (H2O).  
Carbon Dioxide Production No Carbon dioxide is evolved in Glycolysis.   Carbon dioxide is evolved in Kreb’s cycle.  
Occurrence It occurs inside the cytoplasm.   It occurs inside the mitochondria.  
ATP Consumption It consumes two ATP molecules for the initial phosphorylation of substrate molecule.   It does not consume ATP.  
End Products Per Molecule   In the process, net gain is two molecules of NADH and two molecules of ATP for every molecule of glucose broken down.   It produces 6 molecules of NADH and 2 molecules of FADH2 for every two molecules of Acetyl CoA oxidized by it. Two molecules of NADH are liberated during conversion of two pyruvates to Acetyl CoA.  
Connection To Oxidative Phosphorylation  The process is not connected with oxidative phosphorylation.   It is connected with oxidative phosphorylation.  
Substrate Level Phosphorylation In this process, one glucose molecule liberates 4 ATP molecules through substrate level phosphorylation.   In this process, two acetyl residues liberate two ATP or GTP molecules through substrate level phosphorylation.
Oxygen Usage Oxygen is not a requirement for Glycolysis.   Kreb’s cycle uses oxygen as terminal oxidant.  
Net Gain The net gain of energy is equal to 8 ATP.   In Kreb’s, the net gain of energy is equal to 24 molecules of ATP. Six molecules of ATP can be produced from 2NADH2 formed during dehydrogenation of two pyruvates.  
Presence The process occurs in both aerobic and anaerobic respiration.   Kreb’s cycle only occurs in aerobic respiration.  
Enzymes Associated With The Process Phosphohexo isomerase, Hexokinase, Aldolase, Dehydroganase, Kinase, Mutase and Enolase.   Aconitase, Isocitrate dehydroganase, alpha-ketoglutarate denhydroganase, Succinyl synthase, Fumarase and Malic dehydroganase.  

Also Read: Difference Between Nitrification And Denitrification

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