3 Steps of Cellular Respiration

3 Steps of Cellular Respiration

3 steps of cellular respiration make us an understanding of how cells get energy from glucose in short.

As you know, plants get their food by a process called photosynthesis. Photosynthesis helps plants to store energy in the form of glucose. Animals also have glucose where energy is stored and used for growing.


Now, you might have a few questions about living things. Living things make use of this energy by a process called cellular respiration. Cellular respiration plays an important role in releasing the energy to break down glucose to make ATP (Adenosine Triphosphate).



Adenosine Triphosphate, also knew as, ATP is an organic compound, which provides energy in living cells in the body. In this process, each molecule of glucose makes 38 molecules of ATP. Here is the equation below:


C6H12O6 + 6O2 → 6CO2 + 6H2O + ≈38 ATP



Steps of Cellular Respiration

Here are three important steps of cellular respiration.


  1. Steps of cellular respiration 1 (Glycolysis):


The term glycolysis means, “spitting glucose” and it is important for cellular respiration. This essential process happens in the cytosol of the cytoplasm. In this process of glycolysis, it doesn’t need any oxygen to function, which is known as anaerobic respiration. Glycolysis requires glucose to function, which is necessary.


Chemical equation for Glycolysis:


C6H12O6 + 2 NAD+ + 2 Pi + 2 ADP → 2 pyruvate + 2 ATP + 2 NADH + 2 H2O


Two molecules of ATPs need splitting glucose molecule and the two-electron carrier molecules are 2NAD+ (nicotinamide adenine dinucleotide). Next, four molecules of ADP+P (Adenosine Diphosphate) will become four ATP molecules.



See More: Step by step process of glycolysis.


A glucose molecule split by the enzymes and forms into two- molecules of pyruvate as known as pyruvic acid. When the two molecules of pyruvate formed, the energy released four molecules of ATP and the two-electron carriers NADH (Nicotinamide Adenine Dinucleotide + Hydrogen) made.


NowThe chemical reactant of glycolysis was glucose, NAD+, and ADP. This has six-carbon molecules in its structure.

Now, the products of the glycolysis was 2 pyruvic acids, 2ATP, and 2NADH. These pyruvate molecules consists of three carbon atoms.


Furthermore, each molecule consists of hydrogen and two-electron carrier molecules. The body cells can use potential energy efficiently and properly.


  1. Steps of cellular respiration 2 (Krebs cycle or Citric Acid Cycle):


The Krebs cycle or CAC (the Citric Acid cycle) requires multiple chemical reactions that occurs in living things. The Krebs cycle happens in the matrix of the mitochondria in eukaryotic cells.


The Krebs cycle released the stored energy by the method of oxidation of acetyl-CoA.

The Krebs cycle starts with acetyl-CoA, which reacts with the four-carbon molecule known as OAA (Oxaloacetate). During the bonding with OAA, it produces citric acid that includes six carbon atoms. Consequently, the Krebs cycle is also known as the Citric Acid cycle.


This acetyl-CoA comes from pyruvic acids, the final product of glycolysis.


Pyruvic acid don’t participate directly in the reactions of Krebs cycle. It first convert to acetyl-CoA. Acetyl-CoA enters the Krebs cycle.


Four-carbon acceptor molecule influences up the cycle, which does two acetyl-CoA (each contains two carbon molecules). At the same time, two-carbon Acetyl-CoA bond with a four-carbon molecule throughout the cycle, and then forms CO2 and different electron molecules.


Additionally, carbon bonds with pyruvic acids and including the oxygen molecules to make 6CO2. Moreover, 8 NADH and 2 FADH2 electron carrier molecules, and 2 ATP molecules form together, in which cell can use the potential energy.


Remember, a four-carbon acceptor molecule never changes and always states to its first form to take another Acetyl CoA for an extra round for the Krebs cycle. The Krebs cycle recurs continuously and continuously.


As you know, all carbons continue bonding with pyruvic acids, and with the oxygen molecules and becoming carbon dioxide, that is the second step of cellular respiration.


Moreover, the hydrogen atoms, and the electrons on NADH, and FADH2 are left from the original glucose. As a result, the hydrogen atoms, and the electrons of NADH, and FADH2, that will lead to the Electron Transport Chain for the high energy conditions for cellular respiration.


Results of the Krebs cycle are:

  • 4 ATP (contains 2 molecules from Glycolysis)
  • 10 NADH (contains 2 molecules from Glycolysis)
  • 2 FADH2


  1. Steps of cellular respiration 3 (Electron Transport Chain):


The third phase of cellular respiration denotes the Electron Transport chain. Electron Transport Chain implies a group of electron transporters and systems that move from an electron donor to electron acceptors in the center of the mitochondrial membrane.




The reactants of the Electron Transport chain hold 10 NADH electron carrier molecules, 2FADH2, six oxygen atoms from the initial glucose molecule, and especially, 34 ADP and P to bond with ATP Synthase. ATP Synthase is a type of an enzyme that makes ATP continuously for the reactions and cellular respiration. 10 NADH is of 2 molecules from Glycolysis, 8 molecules from the Krebs cycle. 2FADH2 is accepted from the Krebs cycle.


Furthermore, these reactants will transfer the electrons from the electron carrier molecules from high to low transport chain by using active transport. The NADH and FADH2 discharged highly potential energy electrons. On the other hand, the electron transport chain is from the central membrane of the mitochondrion, which occupied the high potential energy electrons along the way.


There are three types of molecules in electron transport system.

  1. Flavoprotein
  2. Cytochrome
  3. Ubiquinones or Coenzyme Q.



As you know, the high potential energy electrons are captured, while the high-energy electrons also transport hydrogen ions from NADH and FADH2 from one side to the other of the central membrane of the mitochondria.

NADH and FADH2 are in the matrix of the mitochondria and accept the electron transport chain to generate ATP repeatedly. 10 NADH electrons have lower levels of energy requirement, so they won’t cause many ATPs. NADH will incidentally give 3 ATPs, while each FADH2 will create 2 ATPs efficiently in the cell. It produces some ATPs because the electrons transferred to the electron transport chain that has insignificantly lower levels of energy than NADH.


This aerobic respiration will result unless the cells in the body do not effectively use the oxygen. Generally, these aspects of the aerobic respiration utilized to determine ATPs from glucose molecules in cellular respiration. Glucose plays a vital role in the Glycolysis, the Krebs cycle, ETC (Electron Transport Chain). One molecule of glucose can potentially cause 38 molecules of ATPs from cellular respiration.

Catabolism of proteins, fats, and carbohydrates in the 3 steps of cellular respiration

Step 1: oxidation of fatty acids, glucose, and some amino acids yields acetyl-CoA.

Step 2: oxidation of acetyl groups in the citric acid cycle includes four steps in which electrons are abstracted.

Step 3: electrons carried by NADH and FADH2 are funneled into a chain of mitochondrial (or, in bacteria, plasma membrane-bound) electron carriers—the respiratory chain—ultimately reducing O2 to H2O. This electron flow drives the production of ATP.



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