Cycle

Cellular respiration cycle is combination of various metabolic processes to derive energy from nutrients or food molecules. All living organisms including bacteria, plants, animals all use cellular respiration process to produce energy. Here we describe all possible aspects regarding cellular respiration cycle.

Cellular respiration cycle is a combination of some metabolic processes that occurs in living cells, which converts food or nutrients into energy units (ATP) and releases different by-products from it. 

Predominantly the respiration process occurs in oxygen rich environment and this kind of cellular respiration is known as aerobic respiration process. 

In absence of oxygen lower organisms also derive energy by breaking sugar molecules. This process is known as anaerobic respiration process or fermentation process.

The cellular respiration process is amphibolic in nature means during this process complex  breaks into smaller molecules as well as the by-products are involved later in constructing other complex molecules. Therefore the respiration process consists of both catabolic and anabolic characteristics, thus the reaction is amphibolic. 

Cellular respiration formula

The basic formula of cellular respiration cycle (typical aerobic respiration) is-

Glucose +6 water → 6 carbon dioxide + 6 water + 36-38 ATP

C6H12O6 + 6O2 –> 6CO2 + 6H2O + 36 or 38 ATP

The equation specifies that during cellular respiration (in presence of Oxygen molecule) one Glucose molecule burns with 6 oxygen molecules to produce 36-38 ATP molecules as energy units. The reaction also releases 6 carbon dioxide molecules and 6 water molecules as by- products. 

Cellular respiration diagram

From the diagram of cellular respiration we can see that there are 4 major steps through which the required energy of cell is produced cyclically. The first step Glycolysis takes place in cytoplasm of cell and the other steps take place in mitochondrial matrix of cell.

Cellular Respiration Cycle from Wikimedia Commons

Cellular respiration reactants

The main reactant in cellular respiration cycle is Glucose and Oxygen molecules. 

In cellular respiration process basically the nutrient or food molecule like carbohydrate, proteins participates in respiration process to produce energy. The main reactant is the oxygen molecule in this process. The oxygen serves as the last electron acceptor molecule during the oxidative phosphorylation process.

Cellular respiration cycle process

Cellular respiration process is combination of various metabolic reactions through which Glucose molecules breaks down.

The cellular respiration process (aerobic) generally undergoes four major steps to generate most of the energy. The steps are including-

• Glycolysis
• Acetyl-CoA formation
• Krebs cycle
• Electron transport chain

Glycolysis

Glycolysis is the first step in the cellular respiration process. In this process 1 Glucose molecule breaks into 2 pyruvic acid or pyruvate molecules. The Glycolysis process occurs in the cytoplasm of a cell. Ten different reactions are involved to facilitate the process. Enzymes involved in Glycolysis pathway are hexokinase, phosphoglucomutase, phosphofructokinase, aldolase, Triose-phosphate isomerase, glyceraldehyde 3-phosphate dehydrogenase, phosphoglycerokinase, phosphoglyceromutase, enolase, pyruvate kinase, etc. 

During this process 1 Glucose (6-carbon) molecule breaks into 2 pyruvate molecules (3- carbon), releases 2 ATP and 2 NADH molecules as by-products.

Glucose (C₆H₁₂O₆) → Pyruvate (CH₃COCOOH) + 2 NADH + 2 ATP

Throughout the process oxygen molecules are not necessary, that’s why Glycolysis occurs in both aerobic and anaerobic respiration processes. This process was discovered by German biochemist Gustav Embden, Otto Meyerhof, and Jakub Karol Parnas and after their names the whole process is known as Embden-Meyerhof-Parnas pathway or EMP pathway.

Acetyl-CoA formation

After the end of the glycolysis pathway the pyruvate converts into acetyl-CoA which later participates in Krebs cycle process. In this process the pyruvate oxidised to form a 2-carbon acetyl group. After the 2-carbon acetyl group bonds with coenzyme -A and produces Acetyl-CoA. 

After Glycolysis the pyruvate enters mitochondria and the acetyl-CoA formation reaction occurs in the matrix of mitochondria. 

This acetyl-CoA formation process is very significant in cellular respiration process. As only though this process the pyruvate converts into acetyl-CoA and acetyl-CoA is the only component which can undergoes Krebs cycle procedure. It is also very significant because due to this process the pyruvate cross the plamsa membrane and travels into the mitochondrial matrix from the cytoplasm of cell.

Krebs cycle

Krebs cycle is the third and most important step in cellular respiration process. It only occurs in an aerobic environment. In case of anaerobic respiration after Glycolysis the pyruvate directly breaks and produces organic by-products to release energy.

In Krebs cycle process the acetyl-CoA breaks and after several reactions produces 2 carbon dioxide molecules, 1 GTP (or ATP), 1 FADH2 and 3 NADH molecules. At around 8 different enzymes are involved in this process such as, Citrate synthase, Aconitase, Isocitrate dehydrogenase, α-ketoglutarate, Succinyl-CoA synthetase, Succinate dehydrogenase, Fumarase, Malate dehydrogenase, etc.

In this process Citric Acid or citrate is produced as the first reaction product. That’s why the cycle is also called the Citric Acid Cycle. As the citrate has three carboxylic groups (- COOH), the reaction is also known as TCA cycle or Tricarboxylic Acid Cycle.

Electron transport chain

It is the last step of cellular respiration cycle where finally most of the energy releases after electron transfer via membrane proteins in the mitochondrial matrix. The NADH, FADH2 molecules transfer electrons and release energy. 

In the aerobic respiration process oxygen molecules act as the last electron acceptor molecule. It produces 36-38 ATP per glucose molecule. It is also known as oxydetive phosphorylation process. In anaerobic respiration process sulphate, nitrate groups act as electron acceptor molecules and produce less amount of energy. 

Cellular respiration cycle types

According to the presence of the Oxygen molecule in the environment we can differentiate cellular respiration types.

There are two types of cellular respiration are found in nature. First one is aerobic respiration process, respiration process in presence of Oxygen molecule. Another one is the anaerobic respiration process, in which oxygen molecules are not necessary. 

• Aerobic respiration
• Anaerobic respiration

Aerobic respiration

Aerobic respiration process is the most common cellular respiration process that occurs in all multicellular living organisms, such as bacteria, fungi, plants, animals, etc.

In this process in the presence of Oxygen molecule the sugar content burns and produces energy for the cell. The whole process consists of four different steps, such as Glycolysis, Acetyl-CoA formation, Krebs cycle and oxidative phosphorylation. After completing the whole process along with 36-38 molecules of ATP, 6 carbon dioxide molecules and 6water molecules are produced as end products. 

Aerobic respiration process from Wikimedia Commons

Glucose +6 water → 6 carbon dioxide + 6 water + 36-38 ATP

C6H12O6 + 6O2 –> 6CO2 + 6H2O + 36 or 38 ATP

Anaerobic respiration

Anaerobic respiration process is mostly occurs in lower groups of organisms body mostly in prokaryotic cells. Anaerobic respiration process is also known as Farmentation process. 

In this process in absence of oxygen molecule carbohydrate or glucose molecule breaks down and produce small amount of energy (2ATP) along with some organic by-products. As it lacks oxygen molecule, inorganic groups like sulphate, nitrate groups serve as electron acceptor and release some energy. In anaerobic respiration only Glycolysis and electron transport chain process is found. 

There is usually two types of anaerobic respiration process is found –

• Lactic acid production
• Alcohol farmentation

Lactic acid production

In the first one Glucose molecule breaks and produce pyruvate during Glycolysis step and after that the pyruvate converts into lactic acid and produce energy.

C6H12O6    →    C3H6O3 + energy (2ATP)

Lactic Acid Fermentation from Wikimedia Commons

Alcohol farmentation

In the second type of anaerobic respiration process one Glucose molecule breaks and produce pyruvate during Glycolysis step and after that the pyruvate converts into ethanol and produce energy along with a carbon dioxide molecule. 

C6H12O6   →    C2H5OH + CO2 + energy (2ATP)

Alcohol fermentation from Wikimedia Commons

To know more about anaerobic respiration process read our article on 4+ Anaerobic Respiration Examples : Detailed Explanations

How does cellular respiration work?

The cellular respiration cycle is a very complicated mechanism through which our body gets required energy from the food we take. 

The process is started when a living organism take  some food. The nutrients from that food are breaks into smaller units like Glucose and through blood flow that reaches each and every cell of the body. After that when the organism breath and takes oxygen, the oxygenated blood also reach each and every cell of the body and the cellular respiration process starts.

At the starting in presence of Oxygen the cell breaks the Glucose and try to produce energy with the help of several enzymes involved in the process. The Glucose molecule undergoes Glycolysis pathway release little amount of energy and converts into pyruvate in the cytoplasm of cell. The pyruvate then transfer into the mitochondrial matrix and oxydised to form acetyl-CoA. Next it undergoes Krebs cycle and after oxydetive phosphorylation process large amount of energy releases. This energy will use for every function of body and that’s gow the cellular respiration process work. 

How long does cellular respiration take in plants?

As cellular respiration is a very quick process but every kind of cell completes respiration in different times. 

A plant cell respires 24 hours a day because the organism needs energy constantly. According to the cell type a basic cell typically completes a cellular respiration cycle within a milliseconds.

How long does cellular respiration take in humans?

As cellular respiration cycle is a very quick process but every kind of cell completes respiration in different times. 

A cell respire 24 hours a day. According to the cell type a cell produces 10 million ATP units per second.

The respiration process depends strictly on the cell type. For example , a muscle cell completes the cellular respiration process more rapidly than a liver cell. 

How long does one cycle of cellular respiration take?

How long one cycle of cellular respiration takes completely depends on the type of that particular cell. 

Typically a cell completes one cycle of cellular respiration within a millisecond and produces energy.

Cellular respiration cycle product

The main function of the cellular respiration cycle is to produce energy from nutrients. So in both of the cellular respiration processes energy molecules are released. 

In the aerobic respiration process along with energy molecules 6 carbon dioxide molecules and 6 water molecules are produced as end products. 

C6H12O6 + 6O2 –> 6CO2 + 6H2O + energy (36 or 38 ATP)

In anaerobic respiration lactic acid production process along with energy lactic acid molecules are produced as the end products of the reaction.

C6H12O6    →    C3H6O3 + energy (2ATP)

In the alcohol fermentation process in absence of oxygen molecules along with energy ethanol and carbon dioxide molecules are produced as end products of reaction.

C6H12O6   →    C2H5OH + CO2 + energy (2ATP)

To know more about fermentation read our article on Is Fermentation Anaerobic Respiration:What,Why,Detailed Facts

As a whole we can say that cellular respiration process is an most important metabolic process for the energy of living organisms. Only through this process a cell breaks nutrients and converts it into energy units ATP. Here we discuss all possible aspects regarding cellular respiration process including steps, types and many more. The role of cellular respiration process in generating energy is immense. 

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Krebs cycle is termed to be the chain of reactions in a cycle format that is catalyzed by the enzymes that includes pyruvate.

On regards to the question for does the Krebs cycle produce water, this cycle tends to eat up water and acetate with these two reduced to carbon di oxide. It uses no oxygen and tends to lose it.

Here there is a derivation of the pyruvate from the nutrients and is converted to Acetyl Coenzyme A which is completely said to be oxidized and then broken down to water and carbon dioxide to generate high energy compounds of phosphate which is also a source of the cell energy. There is no involvement of oxygen here.

Cell respiration is said to be a chain of the metabolic ways that harvest the biochemical energy from the substance that is organic mostly glucose and also then stores it in the form of energy called ATP that is used up for the activities that need up energy for the cell. The major steps or the processes for this needs three steps being glycolysis the Krebs cycle and then oxidative phosphorylation.

Mostly in being particular, with the part of does the Krebs cycle produce water, it contains the cyclic chain of all the reactions that include enzymes via which the pyruvate is converted to Acetyl CoA and then is oxidized to carbon di oxide. With this, the hydrogen ion is said to be removed from the molecules of carbon that helps transfer the atoms and the electrons making a good energy bond.

The carbon di oxide that is made is taken from complete oxidation of the pyruvate and is made to detach itself from the cell in the blood. The hydrogen and the electron carriers, FADH2 and NADH are said to donate the electrons to the electron transport chain to make ATP via oxidative phosphorylation an and then the final metabolic thing is the cell respiration. In the eukaryotes, this cycle tends to occur in the mitochondria while prokaryotes have it is cytoplasm.

Does the Krebs cycle produce water?

The very first step of this process involves Krebs cycle that helps in making of ATP from food via glycolysis and is taken by blood.

With considering the concern for does the Krebs cycle produce water there is no trace of water that is used up by Krebs cycle. It is the outcome finally of the last steps of respiration and the transport chain.

Glycolysis is the process of chemical reaction that is performed by the enzymes. They get onto having the glucose converted to 6 of the carbon sugar onto two of the pyruvate molecules that also have three molecules of carbons. In this method, the two of the molecules of ATP are also made as a couple of the molecules of NADH donating electrons.

At the moment, with does the Krebs cycle produce water, there are many cells that take up an add on step to glycolysis of the level of oxygen is not found. They need no oxygen. This method is quite old and ancient. After ATP tends to keep in energy two of the water molecules are made at this time. It is not till the late in this process that more of the water and ATP is made.

The very next or second step in the process of cell respiration is called to Krebs cycle. It is also termed as the TCA cycle or citric acid cycle. This is seen in mitochondria. Energy is converted into two carriers at this point, FADH2 and NADH along with the coenzyme that mostly plat a good role in making of energy. Some bodies find it hard to make ATP. The cells of the body also use up fatty acids here.

Specifically, the paragraph about does the Krebs cycle create water contains the cyclic chain of all the reactions that include enzymes that convert pyruvate to Acetyl CoA and subsequently oxidise it to carbon dioxide. The carbon di oxide produced comes from the oxidation of organic matter of pyruvate and is used to separate the cell in the blood.

How many water molecules are produced in Krebs cycle?

There is an involvement of one molecule of water while in the making of citrate and the other is made while making of malate from fumarate.

There is a total of 44 water molecules that is made from which there are 34 made from the synthesis of ATP. On addition to it 12 are made from cytochrome oxidase plus the 2 from the enolase and rest is taken by TCA.

There are three of the molecules of water that are used in this step with being 3 different ones. The very first is used while having oxaloacetate converted to citrate, then for having isicitrate transferred to cis aconite and then in the conversion of the fumarate from L malate. Later there is the citrate getting converted from the cis aconite.

It is a balanced reaction and needs an input of two molecules of water. Water is used in many steps but the main point is to have the cycle in motion by balancing the outputs and the inputs. There is always an eye on the acetate. CH3COO- (acetate) + 2 H2O → 2 CO2.

Acetyl-CoA + 3 NAD+ + Q + GDP + Pi + 2 H2O →CoA-SH + 3 NADH + 3 H+ + QH2 + GTP + 2 CO2. This cycle takes up two of the carbons in the level of the acetic acid and then release two molecules of carbon di oxide. This is said to be one of the vital goals in the cycle after having the final combustion done for the rest of the carbon skeletons and the carbohydrate of the amino acids.

The add on oxygen is taken from water and not from carbon di oxide. The rest of the process for combustion consists of the electron transfer from the FADH2 and NADH to the oxygen via the electron transport chain. This is the area where oxygen as two molecules of the gas come into play. It is then reduced to water so that of there is an end to the combustion reaction, fats, the skeletons and the carbs along with + O2 → CO2 + H2O

Does Krebs cycle produce oxygen?

This process can work without the presence of oxygen yet the very final step needs this gas to function and accept electrons.

On regards to the question for does the Krebs cycle produce water, giving out oxygen is not what this does. The process of electron chain transfer shall get jammed if the electrons are not done in the presence of oxygen.

The overall thing that is made by this after using of the acetyl CoA, it makes NADH, FADH2, GTP or ATP along with carbon di oxide. It does not make oxygen but is vital for the final stage of getting the electrons transferred. Oxygen are the final acceptors for electron. The Krebs cycle is not simple and thus is confusing. The processes that are anaerobic needs to oxygen but the rest does.

After the second turn through the Krebs cycle, the original glucose molecule has been broken down completely. All six of its carbon atoms have combined with oxygen to form carbon dioxide. The energy from its chemical bonds has been stored in a total of 16 energy-carrier molecules. These molecules are:

• 4 ATP (including 2 from glycolysis)
• 10 NADH (including 2 from glycolysis)
• 2 FADH2

Oxidative decarboxylation of the pyruvate is the one vital method of the cell respiration that binds the Krebs cycle with glycolysis. It takes place in the mitochondria for the eukaryotes where the three carbon pyruvate is the end result of the method if glycolysis and is then carboxylate to make acetyl CoA being of two carbon molecules and this is done by pyruvate dehydrogenase. It increases cell turnover and helps eliminate accumulated dead skin cells on the epidermis — the top layer of the skin.

Acetyl CoA enters this cycle and the carbon di oxide is then made to lose in the method. There is np involvement of the oxygen in direct basis and makes up some of the ATP and the reductants along with carbon di oxide, FADH and NADH. With no involvement of the gas oxygen, it ceases the view of FAD and NAD. The reaction can be kept in term of equation being- . 

Does the Krebs cycle produces Co2?

The mitochondria said to be the power house of the cell is the house for the Krebs cycle and also makes CO2 that we breathe out.

For this one method, there are two of the dioxide molecules, there of the NADH molecules and one of the GTP or ATP are made. While this makes carbon di oxide it does not have enough energy to make ATP.

The series of this reaction generates two molecules of carbon dioxide and also the reduced form of the FADH2 and NADH. It makes the use of two of the pyruvate molecules and then generates molecules of NADH for energy. There is only little quantity of ATP made after production of carbon dioxide. There is a total of 4 ATP containing two for glycolysis, 10 of NADH from the two including glycolysis and 2 FADH2.

While the Krebs cycle does produce carbon dioxide, this cycle does not produce significant chemical energy in the form of adenosine triphosphate (ATP) directly, and this reaction sequence does not require any oxygen. There are two carbon dioxide molecules produced for every molecule of pyruvate in the Krebs cycle. They are produced during decarboxylation reactions. For one cycle, two molecules of carbon, three molecules of NADH one molecule of FADH2 and one molecule of ATP are made.

Prior to entering the Krebs cycle, the pyruvic acid molecules are altered. Each three-carbon pyruvic acid molecule undergoes conversion to a substance called acetyl-coenzyme A, or acetyl-CoA. During 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 called coenzyme A. This combination forms acetyl-CoA. In the process, electrons and a hydrogen ion are transferred to NAD to form high-energy NADH.

Does the Krebs cycle produce lactic acid?

The pyruvic acid is said to supply the cell that are alive with energy via the Krebs cycle in the presence of oxygen.

If there is no oxygen present, thus there is the fermentation for the making of lactic acid. With the question Does the Krebs cycle produce water, this process makes NADH, FADH and also ATP that are 38 in number.

Pyruvic acid supplies energy to living cells through the citric acid cycle (also known as the Krebs cycle) when oxygen is present (aerobic respiration); when oxygen is lacking, it ferments to produce lactic acid. Pyruvate is an important chemical compound in biochemistry. A turn of the Krebs cycle produces one ATP, three NADH, one FADH₂, and two CO₂. Acetyl-CoA is not produced during Krebs cycle. It is produced from the decarboxylation of a pyruvate molecule, which occurs before the Krebs cycle can begin.

Lactic acid is mainly produced in muscle cells and red blood cells. It forms when the body breaks down carbohydrates to use for energy when oxygen levels are low. Times when your body’s oxygen level might drop include: during intense exercise Lactic acid is an organic acid. It has a molecular formula CH₃CHCOOH. Cellular respiration is a set of metabolic reactions and processes that take place in the cells of organisms to convert chemical energy from oxygen molecules or nutrients into adenosine triphosphate.

Citric acid is the very first product that is made out of this cycle. It gets in pyruvic acid to carbon dioxide by breaking it down. This makes 2 molecules of ATP and then 6 of it is NADH. Oxygen is said to be the ultimate acceptor of electrons in the chain but without the use of oxygen this transport chain is jammed. Muscle cells add fermentation to its and thus pyruvate gets made to lactate.

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