The Krebs Cycle

Krebs Cycle – What it is and End Products


The citric acid cycle, also known as the Krebs cycle or citric acid cycle (CAC), is an eight-step enzymatic pathway in the mitochondria matrix. Its purpose is to oxidize acetate, alpha-ketoglutarate and malate into carbon dioxide and water for energy while converting NADH into NAD+.

The citric acid cycle is also the site of both the synthesis and breakdown of fats, carbohydrates and proteins. Therefore, it is a crucial process for all living organisms. Hans Adolf Krebs first discovered it in 1937 from experiments with citrate fermentation.

The citric acid cycle takes place through ten reactions. They are catalyzed by citrate synthase, aconitase, isocitrate dehydrogenase (alpha and beta subunits), alpha-ketoglutarate dehydrogenase complex (the citrate cleavage enzyme), succinate thiokinase, succinyl CoA synthetases, fumarate, malate dehydrogenase, glutamic acid decarboxylase and the citric acid cycle enzymes (also called respiratory complexes).

There are six citrate synthase enzymes in the citric acid cycle. They represent the four carbons of citrate that initially entered the process of glycolysis and two more that were added later on by the citrate synthase enzymes. This blog post will explore what the Krebs cycle is, what it does to our bodies, and how we can use this information for better health. However, should you choose to skip over this guide, our premium writers are ready to cover you by acing that assignment for you. All you have to do is place an order.

What is Krebs Cycle?

The Krebs cycle is the citric acid cycle. The citric acid cycle is also referred to as the Krebs cycle because Hans Krebs believed that citrate synthases were citric acid dehydrogenase enzymes. In later studies, it was discovered that citrate synthases are not citric acid dehydrogenase enzymes but instead constitute a separate group of citric acid cycle enzymes.

From an evolutionary standpoint, citric acid cycles are found in all living cells. The citric acid cycle is crucial to an organism’s life since it is the citrate synthase enzymes that produce energy for organisms. Therefore, when citric acid cycle enzymes are mutated or absent in an organism, it results in the death of the citric acid cycle.

Citric acid cycles have been found in bacteria and archaea as well as eukarya. This citric acid cycle has been found to have undergone significant changes in bacteria compared with archaea and eukaryotes. The citric acid cycle is also present in organelles within the eukarya. These citric acid cycles exist as mitochondria or chloroplast.

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Brief History of the Krebs Cycle

Hans Krebs discovered the citric acid cycle in 1937 while studying citrate fermentation. In 1947, the citric acid cycle came into notice of the public after Robert B. Brody’s study on cellular respiration at the farm laboratory of the University of Wisconsin-Madison. In 1965, the citric acid cycle was found to be present in chloroplasts of leaf cells and aerobic bacteria.

Krebs cycle – Acetyl – CoA production: At first citrate synthase enzyme catalyzes the formation of citrate from acetyl coenzyme A (acetyl-CoA). Two citrate synthase enzymes are present, and together they form citryl-CoA from acetyl CoA.

Then citric acid, the citrate cleavage enzyme (CCE), separates citrate into oxaloacetate and acetyl coenzyme A. The acetyl – CoA is then used in a series of reactions collectively known as the citric acid cycle. The citric acid cycle is present in mitochondria and chloroplasts of eukaryotes while being absent in the bacteria.

Citric Acid Cycle: citrate cleavage enzyme (CCE) then cleaves citrate into citryl-CoA and oxaloacetate. The citrate cleavage enzyme is also called citrate lyase, citryl-CoA lyase or citric acid lyase.

Another citric acid cycle enzyme (also known as citric acid cycle enzymes) catalyzes the oxidation of oxaloacetates to produce citrates, citric acid cycle enzymes and energy in the form of ATP.

These citric acid cycle enzymes catalyze the citric acid or citrate ion to transfer its electrons to coenzyme Q10 (Q10). Coenzyme Q10 carries electrons from one citric acid cycle enzyme to another citric acid cycle enzyme via electron transporting flavoprotein (ETF). Citric acid cycle enzymes also transfer the citric acid ion’s electron into a series of dehydrogenases.

Citric acid cycle enzymes are then broken down to release acetyl CoA and citrate ions. The citrate ions combine with coenzyme A via citrate synthase enzyme to form citric acid cycle enzymes (citrate). This process is called the citric acid cycle.

How does the Citric Acid Cycle work?

The citric acid cycle is a pathway that takes citrate, acetyl coenzyme A and oxaloacetate (produced from citrate) through a series of enzymatically catalyzed reactions to produce energy via the production of ATP.

A simple way to remember how citric acid cycle works is by breaking it down into 3 (three) stages: citric acid cycle 1, citric acid cycle 2 and citric acid cycle 3.

Citric Acid Cycle 1: in the first stage of the citric acid cycle, enzymes break down citrate to oxaloacetate (also known as α-ketoglutarate). The citric acid cycle enzyme that catalyze citrate breakdown is citrate synthase. The citric acid cycle enzymes that catalyze citrate cleavage are citrate lyase, citryl-CoA lyase or citric acid lyase.

Citric Acid Cycle 2: In the second stage of the citric acid cycle, enzymes break down oxaloacetate to citric acid. Citrate lyase, citryl-CoA lyase or citric acid lyase catalyzes the breakdown of oxaloacetate into citrate and acetyl coenzyme A (acetyl-CoA).

Citric Acid Cycle 3: In the last stage of the citric acid cycle, enzymes break down citric acid to form a citryl-CoA and acetate. Citrate synthase, citric acid phosphatase or citrate (pro-3S)-lyase catalyzes the citric acid breakdown into citryl-CoA and acetyl coenzyme A (acetyl-CoA). Citric acid cycle enzymes are citrate lyase, citryl-CoA lyase or citric acid lyase.

The citric acid cycle produces (four) 4 molecules of ATP for each molecule citrate that enters the pathway. A total of 16 molecules of acetyl coenzyme A and oxaloacetate enter into the citric acid cycle to produce citrate, citric acid and 32 molecules of ATP.

This is a summary of citric acid cycle: citrate synthase: citryl-CoA + HCO3− → citrate + CoA

Citratase/Citrate lyase/Citric Acid Lyase: citrate + acetyl-CoA → citric acid + acetate

Citrate (pro-S)-lyase: citric acid → citrate + acetyl-CoA

Image: Citric Acid Cycle phases

What are the Products of the Krebs Cycle?

End Products are acetyl coenzyme A and citrate

The acetyl group is removed by acetyl-CoA (carbon 3) → acetate + CoA in the second step of the Krebs cycle. The acetate is constantly reentering the Krebs cycle to be converted into acetyl. So, in the end, there will be acetate in the Kreb cycle.

The citrate is by the third step of Kreb cycle (oxidative decarboxylation) → acetyl + coenzyme A + C02, which is converted into acetate and carbon dioxide, while at the same time produces ATP and NADH from ADP and NAD+.

Acetate is created from acetyl coenzyme A, which is produced by the Citric Acid Cycle. The citrate comes from acetyl coenzyme A in the Krebs cycle via oxidative decarboxylation of acetate → acetyl + CoA + C02.

What is Acetyl Coenzyme A?

Acetyl coenzyme A is a multifunctional organic compound derived from acetate and having an acetyl group bound to coenzyme A (that’s how acetyl CoA “gets its name”).

It enters the cycle’s metabolic reactions for oxidation into acetate and ATP. Acetyl coenzyme A is the most used acetyl group carrier in all cells (also called acetyl group donor). It combines with two-carbon fragments from glucose, fatty acids or amino acid to form acetyl group rich building blocks, such as acetoacetyl CoA.

Acetyl CoA is an acetyl-coenzyme A derivative enters the citric acid cycle and produces acetate. This acetate is then converted back into acetyl coenzyme A for further use in metabolic pathways. Acetyl coenzyme A is a carrier of acetyl groups, which are removed during the citric acid cycle.

These acetyl groups can be transferred to acetate thioesters, a reaction catalyzed by acetyl-transferases. Acetate thioesters serve as acyl units in peroxisomes and lysosomes.

Acetyl coenzyme A is acetyl CoA with an acetyl group attached to it. So acetyl coenzyme A is acetate + CoA

What Happens to the Products of the Krebs Cycle?

The Krebs cycle produces acetyl coenzyme A and acetate

Acetyl-CoA is the acetate + CoA produced by acetyl-CoA synthase. The acetyl group comes from acetate, which is created in the Krebs cycle (oxidative decarboxylation).

Acetyl group is transferred to CoA by acetyl-CoA acetyltransferase. Acetate also comes from acetyl group transfer. The acetate produced in the Citric Acid cycle is converted into acetyl group by acetate dehydrogenase and then combines with coenzyme A to become acetyl coenzyme A.

Acetate also comes from acetate produced from acetyl group transfer. Acetate dehydrogenase catalyzes the conversion of acetoacetyl CoA to acetate. Acetyl group transfer catalyzes the opposite reaction.

Acetate + ATP produces acetyl CoA + ADP. In oxidative decarboxylation; pyruvate is converted into acetyl coenzyme A by combining with coenzyme A. Then, the two-carbon fragments of a glucose molecule, fatty acids or amino acids, are combined with the acetyl group to form larger molecules.

Acetyl coenzyme A can be used for lipid synthesis and many other functions, including biosynthesis of steroids, cholesterol, fatty acids and ketone bodies. It will convert into citric acid in the Krebs cycle again. Acetate can be used for fatty acids synthesis, or the acetate can be converted into Glutamate then converted back to Acetyl CoA in another process.

Acetyl group can be removed from acetic acid (or vinegar). The removal of a proton is called deacetylation and occurs spontaneously when H3O+ is added to acetic acid.

Acetate + H 2 O → CO2 + acetyl CoA + H 3 O+ Acetyl group is removed from acetic acid by deacetylation, a reaction catalyzed by vinegar bacteria on the surface of grapes during fermentation.  

When there is extra carbon in the body, they will be transferred into other carbon-rich products. These extra carbons are converted into more acetyl groups; the formula is CnHm + 3O2 → CO + 2H2O + 2 Acet. (C6H12O6 + 9O2 → 6CO2 + 6H2O + 4Acet).

What Are the End Products of Glycolysis

The citric acid cycle is a series of enzyme-catalyzed reactions that takes acetyl groups from acetyl-coenzyme A molecules and attaches them to oxaloacetate. It produces two 3-carbon fragments (oxaloacetate and acetate), which provide an acetyl group for acetyl CoA synthesis in the next cycle.

The products of the two cycles, pyruvate and acetyl coenzyme A, are then cleaved by an enzyme called pyruvate dehydrogenase complex. The acetyl group is transferred to coA; from there, it enters the citric acid cycle. And acetate part of acetyl CoA goes into the mitochondria/peroxisomes and is converted into acetyl-transferase to acetic acid.

Acetic acid goes out of the cell and into the bloodstream, where it is picked up by the liver and broken down to release two acetate molecules used in gluconeogenesis.

It should be noted that the energy released from glucose metabolism through these two pathways (glycolysis and the citric acid cycle) is used to generate 18 ATP molecules.

Though the net energy generated by these reactions is low, every cell of every organism on earth occurs. This process allows all organisms to quickly convert glucose into adenosine triphosphate (ATP), a universal form of energy that is readily available for use by all of the body’s cells.

CO2 Assimilation (HCO3−) in Land Plants and Algae

Six molecules of CO2 are first converted into triose phosphate, each molecule resulting from the oxidation of one molecule of RuBP (ribulose 1,5-bisphosphate).

Two molecules of the triose phosphate are converted into glyceraldehyde-3-phosphate (GAP), with the removal of two HCO3− ions and two electrons.

The remaining four molecules of CO2 are transformed into erythrose 4-phosphate (EP) by way of carbon dioxide fixation, each molecule being reduced to one molecule of 3-phospho-glycerate (PGA). The two electrons initially removed from CO2 are used to reduce two molecules of NADP+ into NADPH.

Two additional molecules of glyceraldehyde-3-phosphate and two more HCO3− ions are synthesized by reactions with the triose phosphate so that a total of 10 molecules of GAP and two molecules of PGA are produced.

These 12 molecules yield 6 CO2 molecules (12) –> 10 glyceraldehyde 3-phosphate (GAP) + 2 pyruvate + 2 glucose (PGA + 2 HCO3−) (8).

It should be noted that plants utilize about 5% of the carbon dioxide in the atmosphere for photosynthesis.

HCO3− is very easy to assimilate in plants and algae since it can be incorporated into any of its organic compounds or used primarily as a source of H+ ions necessary for transport processes (indole-acetic acid).

The other products of carbon dioxide assimilation are pyruvate and Adenosine triphosphate molecules.

Plants use the pyruvate molecules for starch biosynthesis or converted them into organic acids, such as malic acid. The latter is transported to the mitochondria of chloroplasts, where it is used in the production of NADPH.

The products of photosynthesis shuttled to the root system are either stored as starch or used immediately in respiration. When products of photosynthesis are directed to the chloroplast, they can be stored for later use (for example winter), and thus serve to store solar energy, which plants need for their survival.

Energy obtained from sunlight during photosynthesis is used to convert into the various organic compounds that plants need. The CO2 (carbon dioxide) fixed during photosynthesis is transformed into carbohydrates with the use of water and light energy and a supply of electrons from NADPH produced by the chloroplast.

The products of this reaction may be either carboxylic acids or alcohols. The latter can be converted into either organic or inorganic acids. Since the products of photosynthesis are derived from CO2, which is abundantly available, plants need not compete with other organisms for its acquisition (as do herbivorous animals).

The same situation does not apply to animals who must rely on glycolysis and gluconeogenesis to produce ATP molecules.

In photosynthesis, plants use about 5% of the CO2 in the atmosphere to synthesize organic compounds. This is due to their ability to assimilate the bicarbonate ion (HCO3−) into organic compounds essential for plant growth and survival.

Plants are able to utilize carbon dioxide for its conversion into organic compounds in the presence of light and water, a process called photosynthesis. The main products of photosynthesis are carbohydrates that are used to maintain average plant growth and development as well as to repair the damage.

Furthermore, HCO3− requires minimal energy input to assimilate CO2 into glucose (6 ATP molecules). This fact, coupled with the minimal amount of carbon dioxide that plants assimilate, leads to the conclusion that a large portion of solar energy utilized in photosynthesis is rejected as heat.

Hence, during light reactions in photosynthesis (in chloroplasts), most photons excite electrons that are energized to higher energy levels. These extra electrons become unstable, and they are converted into a new chemical compound called NADPH.

The product of the first stage of photosynthesis is called GAP, which has three carbons; 10 molecules of GAP yield two molecules each of glucose (PGA) and fructose 1, 6-diphosphate (FDP), and two molecules of pyruvic acid (PYR).

The enzyme phosphoglucoisomerase synthesizes these products.

Since GAP is a three-carbon molecule, after its conversion into PGA + FDP, six carbon dioxide molecules are assimilated per 1 glucose and fructose 6-phosphate molecule; these products are the end products of photosynthesis.

The glycolytic pathway starts with the formation of fructose 6-phosphate from glucose (Fig. 2). This reaction is catalyzed by PFK, a bifunctional enzyme: PFK-1 has glucokinase activity (catalyzes the phosphorylation of glucose to form glucose 6-phosphate) and gluconeogenic activity (catalyzes the reverse of this reaction, i.e., glucose 6-phosphate is converted into glucose); PFK-2 has only gluconeogenic activity.

PFK-1 catalyzes the conversion of fructose 1,6-diphosphate to glyceraldehyde 3-phosphate and dihydroxyacetone phosphate; the second of the above reactions are catalyzed by fructose 1,6-diphosphate aldolase (aldolases are enzymes that utilize two molecules to produce one).

The next step in glycolysis involves the conversion of glyceraldehyde 3-phosphate to 1,3-bisphosphoglycerate (BPGA) with the use of ATP and glyceraldehyde 3-phosphate dehydrogenase.

PYR is formed in glycolysis as the result of two reactions: a condensation reaction that involves the conversion of BPGA into 3-phosphoglycerate (PGA) and phosphoglycerate kinase (PGK), and a decarboxylation reaction catalyzed by enolase.

The end products of glycolysis are oxidized in oxygen to form CO2 (aerobic respiration) and H2O (glycolysis is an aerobic process). Since pyruvic acid has three carbon atoms, one molecule can yield (4) four carbon dioxide molecules.

Furthermore, pyruvic acid can be converted into PYR via the enzyme pyruvate dehydrogenase in a reaction that requires NAD+ and produces more NADH. The reaction is catalyzed by pyruvate dehydrogenase complex (PDC), made up of three enzymes: E1, E2 and E3.

The next stage of aerobic respiration involves the Krebs cycle (also called tricarboxylic acid cycle- (TCA cycle) or citric acid cycle), which reduces carbon compounds upon oxidation of PYR.

The net result in aerobic respiration is that one molecule of glucose (C6H12O6) can yield about 36 molecules of ATP and other carbohydrate-derived energy sources, such as NADPH, FADH2 and CO2.

During the Krebs cycle, the oxidation of PYR is coupled to the reduction of CO2 and H2O.

The end products of glycolysis and aerobic respiration are ATP (energy) and reduced carbon compounds used for biosynthesis processes. The reduced carbon compounds formed during aerobic respiration will be incorporated into glucose molecules, fatty acids and ketone bodies.

The Krebs cycle is a cyclic process, i.e., it can continue for as long as oxygen is present in the cell (the last stage of aerobic respiration).

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What are Anabolic and Catabolic Reactions?

The anabolic reaction is a metabolic process that requires energy (ATP) and produces new molecules. The opposite of anabolic reactions is called catabolic reactions.

Catabolism (from Greek, katabole “broken down”, from kata-, “down” + balein, “to throw”) is the set of metabolic pathways in which smaller molecules are converted into larger molecules.

These processes involve the breaking down (hydrolysis) of larger molecules. Catabolic reactions are closely associated with energetics and the formation of ATP, which is essential for all anabolic reactions to proceed.

Image: Anabolic and Catabolic Reactions

Catabolism can be quite varied as it includes the breakdown of large molecules such as polysaccharides, lipids, nucleic acids, and proteins.

There are two main types of catabolic reactions: anaerobic and aerobic.

The anaerobic process is the breakdown of glucose in the presence of phosphates, by glycolysis (the conversion of glycogen into lactic acid, with the formation of pyruvic acid). This doesn’t require oxygen.  Anaerobic reactions are generally much faster than aerobic ones.

The aerobic process is the breakdown of glucose in the presence of oxygen and is a series of metabolic steps called glycolysis, Krebs cycle (also known as citric acid cycle) and oxidative phosphorylation. Aerobic reactions take place in mitochondria, which produce ATP. End products of glycolysis are used in aerobic respiration. The main end product is pyruvate, which is converted into acetyl coenzyme A (acetyl CoA), which enters the Krebs cycle.

The principal catabolic transformation mechanism is hydrolysis, in which a compound is cleaved into two smaller fragments or subunits as part of the breakdown process.

In the human nutrition context, the term metabolism refers to all the chemical reactions in the body. Catabolism involves breaking down large molecules such as carbohydrates, lipids (fats), and proteins into smaller ones. For example, fats are broken down into glycerol and fatty acids, carbohydrates are broken down into glucose, proteins into amino acids.

How Many ATP Are Produced in the Krebs Cycle?

There are several ATP produced in the Krebs cycle; almost 36 ATP synthase molecules in the Krebs cycle are produced by aerobic respiration. 

The enzyme that catalyzes the addition of an inorganic phosphate group to ADP, forming ATP, is an integral membrane protein complex called ATP synthase.

The total number of ATP produced by oxidative phosphorylation in mitochondria of 8 x 10 cells has been estimated as 3 x 10. The ATP synthase is composed of five individual proteins that span the membrane of mitochondria in a “figure eight” shape.

It consists of three cryo-electronically distinct subunits (alpha, beta and gamma). ATP synthase catalyzes the chemical energy from adenosine diphosphate (ADP) and inorganic phosphate into a transmembrane proton gradient. This is then used to create the electrochemical potential that produces ATP from ADP and inorganic phosphate.

ATP is essential for every life form because it is the primary source of energy for a cell. It is a crucial molecule that helps us to function correctly. However, our body stores ATP in limited quantities. It is crucial to replenish the supply of ATP continuously.

The Krebs cycle produces only two high-energy phosphate bonds per glucose molecule metabolized, but the small amount of ATP produced during other reactions is also used. This results in a total of 38 ATP molecules produced from one molecule of glucose.

Krebs Cycle Reactants

Krebs cycle reactants are pyruvic acid, PEP, oxaloacetic acid (OAA), and NAD+.

The net gain of one molecule of pyruvic acid in the aerobic respiration process is two molecules of CO2 + GTP.

What Are the End Products of Glycolysis and the Krebs cycle in prokaryotes?

The end products of glycolysis is prokaryotes, pyruvic acid and its derivatives, such as acetyl-CoA, succinyl-CoA, and lactate. These reduced carbon compounds will be incorporated into fatty acids and other biosynthetic pathways.

The primary end product of aerobic respiration in prokaryotes is ATP. The net gain of one molecule of pyruvic acid in the aerobic respiration process is two (2) molecules of CO2 + GTP.

What Are the Final Products of the Krebs Cycle?

The final products of Citric acid cycle are CO2, Acetyl-CoA (AcCoA), FADH 2, NADH + H, and ATP.

The combination of oxygen with hydrogen produces water as the final product.

Importance of the Krebs Cycle

The importance of the Krebs cycle is that it produces pyruvic acid from glucose. Pyruvic acid is one of the end products in Glycolysis, and also, at the last stage of the Krebs cycle, ATP is produced.

How Does Krebs Cycle Work in our Body?

The primary role of the Krebs cycle in our body is that it produces energy. Both pyruvic acid and oxaloacetic acid are intermediate molecules in the Krebs cycle.

In the cycle, two carbon fragments from pyruvic acid get attached to a CO2 molecule to form a 4-carbon molecule called citric acid that combines with another acetic acid element (from PEP molecule) to form a 6-carbon compound called a Krebs cycle intermediate.

This is the end product of glycolysis, anaerobic respiration or fermentation. The Krebs cycle produces ATP by capturing the energy released during high-energy reactions that occur inside mitochondria.

Aerobic respiration combines all the reactions, which occur in the glycolysis and citric acid cycle. The final compound of response is the same as the end product in aerobic respiration; it is just that the starting compound changes during this process.

What Does the Enzyme Pyruvate Dehydrogenase do, And How Does it Work?

This enzyme is present in different forms, i.e. E1 complex, E2 complex and E3 complex. The E1 complex contains the enzyme pyruvate dehydrogenase that accepts Co2 and converts it into acetyl-CoA. This is done in coenzyme A and NADH molecules.

The succinyl-CoA molecule produced from this reaction gets converted to succinate by the enzyme CoQA reductase in an NAD+ environment. The succinate produced is further converted to fumarate by the enzyme fumarase in an NADH environment.

The enzyme FAD synthase then converts succinate into malate with the help of oxaloacetate and another molecule of FADH2. And finally, malate gets converted into pyruvate through the action of the malic enzyme.

It is a complex reaction that involves the transfer of hydrogen atoms and electrons between multiple coenzymes (i.e., NADH, FADH2, and Coenzyme A). This process requires magnesium and ATP to work correctly.

When Do We Use Krebs Cycle in our Everyday Lives?

At the last stage of Aerobic Respiration, pyruvic acid is converted into Acetyl-CoA. Acetyl-CoA then enters into the Krebs cycle and produce 36 ATP molecules. Daily, our body produces 16 to 20 moles of ATP via this process, which helps produce glucose for energy purposes.

The reactions in the citric acid cycle are oxidation-reduction reactions because enzymes involved in these reactions require coenzyme and NADH for transferring electrons.

In oxidation-reduction reactions, reduced forms (NADH) donate their hydrogen atom to oxidized forms (NAD+) and both these forms are produced in this process.

For each glucose that provides 36 molecules of ATP, six molecules of ATP are formed from the oxidation of 1 molecule of pyruvate. Ten NADH + 3 molecules of FADH2 are converted into seven molecules of CoQ10 (2 for each molecule) and one molecule of ATP.

What Is the Role of Enzymes in the Krebs Cycle?

The main work of enzymes is to accelerate reactions by increasing rates of reaction. Enzymes are made up of a specific protein (conjugated protein) and coenzyme that is complex to form an enzyme that works as a catalyst in chemical reactions.

A Krebs cycle enzyme can work just like the TCA cycle enzyme because its molecular structure is similar to the mitochondrial matrix where TCA cycles occur.

In addition to this, the electron transport chain starts working when all Krebs cycle enzymes are in an active form and ready to accept molecules that enter into it.

What Is the Role of Coenzymes NAD+ AND FAD in the Krebs Cycle?

The exact explanation for the action of coenzyme NADH is not known yet, but according to research carried out so far, they play an essential role in electron transport.

Coenzyme FAD acts like a machine that is capable of adding another H+ to the molecule. Once it gets reduced, it’s chemical structure changes and becomes ready to accept another hydrogen atom from other molecules.

In this way, one energy-rich molecule is produced with a lot of electrons and protons.

What difference is seen between Pyruvate molecules in glycolysis and the Krebs cycle?

The main difference between pyruvate molecules in the glycolysis and Krebs cycle is that the former gets converted into Acetyl-CoA while the latter produces Acetyl-CoA from Pyruvic acid.

What Happens to 2 Carbon Atoms Produced During this Process?

The first carbon atom of acetyl-CoA get attached to oxaloacetate and the second one becomes part of the Acetyl-Threonine group. The latter is then attached to a Glyceraldehyde 3 phosphate molecule, forming 1,3 bisphosphoglycerate or GAP. The above process occurs only in case when alcohol is present in our blood. Acetyl-CoA is then joined with the Citrate molecule to form a (4) four-carbon compound called Succinyl-CoA, and the process ends at this stage.

What Essential Features of the Krebs Cycle Enables It to Produce 36 ATP Molecules?

The main difference between TCA cycles and the Krebs cycle is that the latter takes place in the mitochondrial matrix, and it is a process in which oxygen free radicals are reduced to form water.

The TCA cycles take place in a non-living system where oxygen cannot enter into it (CO2+H2O+light energy->carbon base). Further, the Krebs cycle has four essential features as under:

1) It is a cyclic process in which various sequential reactions take place to synthesize ATP from ADP & H+.

2) The inner mitochondrial membrane of the mitochondria acts as a semi-permeable structure that allows the flow of substances needed by it.

3) NADH and FADH2 carry out redox reactions in the Krebs cycle by reducing free radicals to water.

4) Free radicals are kept under control and destroyed when oxygen is present in the mitochondria.  

How Does Respiratory Alkalosis Happen?

Respiratory alkalosis occurs when the person breathes too much air (hyperventilation), stirs up unbreathable CO2. A drop in bicarbonate ion levels can also cause respiratory alkalosis.

Cells use oxygen in the mitochondria to convert glucose and fatty acids into energy. The byproducts of that conversion include heat, water, CO2, and waste products (e.g., lactic acid).

Typically, carbon dioxide is reabsorbed through the lungs and eliminated from the body.

CO2 is not directly harmful to the body; in fact, it’s a regular product of cellular respiration that controls other compounds like bicarbonate and carbonic acid. However, too much CO2 can deplete your blood of oxygen or cause an irregular heart rate or rhythm (arrhythmia). This condition is called respiratory alkalosis.

What Happens When a Person Has Too Much CO2 in their Body?

Too much CO2 (Carbon dioxide) in your body can cause respiratory alkalosis.

CO2 is a byproduct of cellular respiration, which occurs in the mitochondria. However, more CO2 can be produced outside the cell than can be disposed of inside the cell. The excess CO2 (carbonic acid) triggers an increase in ventilation to rid your body of excessive CO2. This depletes your body of CO2 and helps restore the acid-base balance.

CO2 is an essential measure in determining your respiratory status. It also reveals information about blood pH abnormalities that may occur in certain medical conditions, such as acute respiratory distress syndrome (ARDS) or heart failure.

Extra CO2 in your blood is a regular occurrence that occurs when you breathe out. When your body does not eliminate enough carbon dioxide, it builds up and triggers the opposite of respiratory acidosis: respiratory alkalosis. There is too much CO2 being breathed out by the lungs than there is being taken in in this condition.

This condition can be life-threatening, especially in severe conditions such as pneumonia or acute respiratory distress syndrome.

What Happens When a Person Has Too Much HCO3- in their Body?

Too much bicarbonate is highly unlikely, but if it did occur, respiratory alkalosis would result. This happens when hypocapnia occurs (low blood levels of CO2). This problem only occurs in extreme cases, which would cause the symptoms of respiratory acidosis.

Bicarbonate is a regulator of pH levels in your blood. It helps maintain the excretion or absorption of other ions and molecules by keeping blood pH well-regulated.


The citric acid cycle, also known as the Krebs cycle or citric acid cycle (CAC), is an eight-step enzymatic pathway in the mitochondrial matrix. From an evolutionary standpoint, citric acid cycles are found in all living cells. The citric acid cycle is crucial to an organism’s life since it is the citrate synthase enzymes that produce energy for organisms.

 Therefore, when citric acid cycle enzymes are mutated or absent in an organism, it results in the death of the cell and consequently no more production of ATP molecules. This can cause any number of symptoms depending on what other processes rely on this cellular respiration process for their own function.

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