Tag: Glycolysis

Introduction

A metabolic pathway consists of a series of chemical reactions in which a certain molecule is transformed from one product to another. Enzymes catalyze each step in a metabolic pathway. The anabolic pathway involves biosynthesis, or the creation of new molecules, and is a constructive mechanism. On the other hand, the catabolic pathway is a degradative process that causes compounds to break down. An energy input would be necessary for both of these kinds of pathways. An amphibolic pathway is a type of biological process that involves both anabolism and catabolism. In these pathways, the catabolic end products or intermediates are utilized in anabolic pathways as precursors and provide free energy for the production of further molecules.

Glycolysis -an amphibolic pathway

In the metabolism of plants, animals, and numerous microbes, glucose plays a crucial role. It is employed to carry out aerobic or anaerobic respiration, which produces energy in the form of ATP. Through a sequence of processes, glucose is converted to two molecules of pyruvate during glycolysis. Although it is primarily understood as a catabolic process, some of the pathway’s intermediates are also used in the production of a few different biomolecules. Hence glycolysis is an amphibolic pathway. 

The following shows how glycolysis is an amphibolic pathway-

• The pentose phosphate pathway uses glucose 6-phosphate, to produce ribose 5-phosphate, which is then employed in the synthesis of nucleic acids.
• The process that produces glyceraldehyde 3-phosphate also produces glycerol, which is necessary for the synthesis of phospholipids.
• Pyruvate, the final byproduct of the glycolytic process, is further converted to Acetyl-CoA, which is utilized in the production of fatty acids.
• The NADPH generated in the pentose phosphate pathway, which utilizes glycolysis intermediates, is employed as a reducing agent to enable a number of anabolic processes, such as the production of fatty acids, nucleic acids, carotenoids, etc.
  

Krebs cycle -an amphibolic pathway

In aerobic organisms, the Krebs Cycle (also known as the TCA cycle) is amphibolic because it participates in both catabolic and anabolic processes. The Krebs Cycle, which takes place in the mitochondria, results in the production of ATP, NADPH, and FADH2.

The Krebs Cycle’s key component, acetyl-CoA, is produced from-Pyruvate oxidation (from glycolysis), Fatty Acids (Beta-oxidation), and Amino acid degradation.

• Krebs Cycle is catabolic because it completely oxidized acetyl-CoA into carbon dioxide (CO2).
• The Krebs cycle is also referred to as being anabolic since various biomolecules, such as nucleic acids, fatty acids, amino acids, and porphyrins, are synthesized from its intermediates.
• At each cycle turn, the Krebs cycle intermediate oxaloacetate is created again in order to condense with a new molecule of acetyl-CoA which continues the cycle.

Other intermediates of the Krebs Cycle serve the following anabolic functions-

• Porphyrins, which are necessary for the synthesis of myoglobin and hemoglobin, are created using succinyl-CoA.
• Oxaloacetate is the starting material for synthesizing amino acids such as proline, alanine, glutamate, and aspartate. Purines are created by using glutamate and aspartate amino acids.
• In the mitochondria, oxaloacetate is also transformed into phosphoenolpyruvate, which is then transformed into glucose via the gluconeogenesis pathway. Malate is also employed for gluconeogenesis.
• ɑ-Ketoglutarate is a component in succinate synthesis.
• By way of transamination processes,ɑ- ketoglutarate is also utilized in the synthesis of glutamate and pyruvate.
• Acetyl-CoA, the precursor for the production of fatty acids and cholesterol, is formed when citrate and CO2 interact.
• The fatty acids are further metabolized into triacylglycerols and diacylglycerols and ultimately form the phospholipids.
• The cholesterol formed is then used to synthesize steroids and bile acids.

How is the Respiratory Pathway an Amphibolic Pathway?

• Complex molecules are converted into simpler ones during respiration, which gives organisms energy in the form of ATP.
• The four steps of respiration are glycolysis, pyruvate oxidation, the tricarboxylic acid cycle, and oxidative phosphorylation.
• These include the tricarboxylic acid cycle(TCA) and glycolysis, which both generate intermediates used in the creation of numerous other biomolecules.
• The pentose phosphate pathway uses glucose 6-phosphate, the first glycolysis intermediate, to branch off from glycolysis.
• The formation of ribose 5-phosphate, which is produced through the pentose phosphate pathway, is crucial for the biosynthesis of nucleotides.
• Erythrose 4-phosphate, which is necessary for the synthesis of aromatic amino acids like tryptophan, phenylalanine, and tyrosine, is also produced by the pentose phosphate pathway.
• As a result, it may be said that the respiratory system is an amphibolic pathway since it produces a number of precursor metabolites that are used in the biosynthesis of several cellular components. It also involves the oxidation of organic carbon into carbon dioxide and water, which releases energy.

Summary 

• Amphibolic pathways are both catabolic and anabolic.
• Glycolysis intermediates, glucose 6-phosphate, and glyceraldehyde 3-phosphate are used to produce purines and phospholipids, respectively.
• Krebs Cycle is a well-known amphibolic process, and its intermediates are employed in the synthesis of different amino acids, fatty acids, sterols, nucleic acids, etc.
• The respiratory pathway is referred to as amphibolic since it contains a variety of catabolic intermediates that act as anabolic precursors.

Frequently Asked Questions

1. Difference between Krebs cycle and Glycolysis
Ans:

Glycolysis	Krebs Cycle
Occurs in the cytoplasm	Occurs in the mitochondrial matrix
It marks beginning of respiration	It is the 3rd step in respiration.
It is a linear pathway	It is a cyclic pathway
Glucose converted to 2 molecules of pyruvate.	Acetyl-CoA is converted into carbon dioxide.
No release of CO2	CO2 released
Net ATP generated = 8 ATP	Net ATP generated = 24

2. What are two forms of glycolysis?
Ans: The two forms of glycolysis are Aerobic and anaerobic glycolysis-

• Pyruvate enters the citric acid cycle under aerobic conditions and proceeds through oxidative phosphorylation, which results in the net synthesis of 32 ATP molecules.
• Pyruvate is converted to lactate under anaerobic conditions by the process of anaerobic glycolysis.

3. Who gave the term Amphibolic Pathway?
Ans: In 1961, B. Davis gave the term amphibolic Pathway. It is a pathway that involves both anabolism and catabolism.

Introduction

All of the body’s cells require energy to support various metabolic processes, thus every living thing engages in cellular respiration to release energy, which is then stored in the form of ATP. After ingestion, food is transported into the stomach via the oesophagus, where stomach acids and enzymes break it down into several smaller bits, including glucose. Since glucose is the most prevalent monosaccharide and the first substrate for the metabolism of carbohydrates, where it is broken down to release energy, glucose and ATP are the molecules that carry the energy.

Definition of Cellular Respiration

All plant and animal cells produce energy through a process called cellular respiration (excluding RBCs). Food glucose is broken down into carbon dioxide, water, and energy with or without oxygen throughout this process. As a result, it liberates ATP and releases carbon dioxide as a waste product (adenosine triphosphate).

Difference between Respiration and Breathing

Respiration	Breathing
Respiration is the physiological process of breathing in and breathing out. Energy is released from cells during the chemical breakdown of food-derived glucose.	Breathing is the movement of oxygen into the body from the outside environment and the release of carbon dioxide from the lungs into the outside environment.
It is categorised into cellular respiration and physiological respiration.	Since breathing is a form of respiration, it is often referred to as physiological respiration.
In cells, and notably in cellular organelles like the cytosol and mitochondria, cellular respiration takes place.	It takes place in the lungs.
There is the involvement of enzymes.	There is no involvement of enzymes.
It produces ATP that is converted into energy.	It does not produce energy.

Glycolysis

• One glucose molecule is broken down into two pyruvate molecules in this process, which also results in the creation of ATP. 
• Every cell in the body contains it in the cytoplasm. Hexokinase enzyme converts glucose to glucose-6-phosphate.
• By using phospho-hexose isomerase, which are isomers of one another, glucose 6-phosphate is converted to fructose 6-phosphate. 
• By phosphorylating fructose 6-phosphate, phosphofructokinase catalyzes the irreversible conversion of fructose 6-phosphate to fructose 1,6-bisphosphate.
• Aldolase catalyzes the breakdown of fructose 1,6 bisphosphate into glyceraldehyde 3-phosphate and dihydroxyacetone phosphate.
• The reversible interconversion of glyceraldehyde 3-phosphate and dihydroxyacetone phosphate is carried out by phosphotriose isomerase.
• Glyceraldehyde 3-phosphate is converted to 1,3-bisphosphoglycerate by glyceraldehyde 3-phosphate dehydrogenase. 
• In this stage, \(NA{D^ + }\) is converted to \(NAD{H^ + }\) and \({H^ + }\), which adds a phosphate group to glyceraldehyde 3-phosphate. With the creation of ATP, the enzyme phosphoglycerate kinase converts 1,3-bisphosphoglycerate into 3-phosphoglycerate.
• Phosphoglycerate mutase converts 3-phosphoglycerate into 2-phosphoglycerate, and these two substances are isomers. 
• Enolase transforms 2-phosphoglycerate into the highly energetic molecule phosphoenolpyruvate once water is removed. 
• In the presence of pyruvate kinase, phosphoenol pyruvate is transformed into pyruvate along with the creation of ATP.       
•  

Generation of ATP: Two pyruvates, two NADH, and two ATP molecules are the final products of glycolysis. Due to the conversion of glucose into two pyruvates, 8 ATP molecules are produced.

Krebs Cycle

Acetyl CoA is converted into carbon dioxide and water by some chemical processes called Krebs cycle.

• Pyruvate is converted to acetyl CoA through oxidative decarboxylation by pyruvate dehydrogenase. 
• The elimination of carboxylate groups to create carbon dioxide is known as oxidative decarboxylation. Acetyl CoA and oxaloacetate are condensed by citrate synthase. 
• Aconitase converts citrate into isocitrate.
• Isocitrate dehydrogenase uses oxidative decarboxylation to change the isocitrate to oxalosuccinate, which is then transformed into -ketoglutarate. 
• By removing the carboxylate group from ketoglutarate and generating carbon dioxide, the enzyme ketoglutarate dehydrogenase transforms ketoglutarate to succinyl CoA. 
• Succinate thiokinase causes succinyl CoA to be converted to succinate. A phosphorylated group is added to GDP to create GTP, which is then converted into ATP by a protein called nucleoside diphosphate kinase. 
• By catalysing the conversion of succinate to fumarate and producing \(FAD{H_2}\), succinate dehydrogenase.
• By including water, fumarase catalyses the conversion of fumarate to malate.
• Malate dehydrogenase converts malate to oxaloacetate and generates NADH in the process. 
• The cycle is maintained by mixing the oxaloacetate with more acetyl CoA molecules.
• 

Generation of ATP: In the Krebs cycle, 12 ATP is produced as a result of the production of 2 \(C{O_2}\), 3 NADH, and 1\(FAD{H_2}\).

Electron Transport Chain or Terminal Oxidation or Oxidative Phosphorylation

The proton gradient created by the electron transport chain (ETC), a chain of proteins that transports electrons through the mitochondrial membrane, powers ATP generation. A series of ETC enzyme complexes: 

• NADH-ubiquinone reductase – Complex I
• Succinate CoQ reductase – Complex II
• Ubiquinone-cytochrome c oxidoreductase – Complex III
• Cytochrome oxidase – Complex IV 
• ATP synthase – Complex V 

Through electron carriers such as flavoproteins, cytochromes, coenzyme Q, nicotinamide nucleotides, and iron-sulfur proteins, these catalyze the transport of electrons.

Since energy is lost during the passage of electrons through ETC, the ATP synthase complex uses the energy to produce ATP from ADP, a procedure known as oxidative phosphorylation. 32 ATP molecules are generated during oxidative phosphorylation and ETC.

Differences between Glycolysis and Krebs Cycle

Glycolysis	Krebs cycle
It involves both aerobic and anaerobic respiration.	It involves only aerobic respiration.
The substrate substance is glucose.	The substrate material is acetylAcetyl CoA.
Glycolysis takes place in the cytoplasm.	The KrebsKrebs cycle takes place in the mitochondria.
It consumes two molecules of ATP.	It does not consume ATP.
Carbon dioxide is released in glycolysis.	Carbon dioxide is not released in the Krebs cycle.
It is a linear enzymatic reaction.	It is a non-linear pathway.
It occurs in both eukaryotes and prokaryotes.	It occurs in eukaryotes.

Difference between Aerobic and Anaerobic Respiration

Summary 

All plant and animal cells produce energy through a process called cellular respiration. Due to the conversion of glucose into two pyruvates, 8 ATP molecules are produced in glycolysis. In the Krebs cycle, 12 ATP is produced as a result of the production of 2 \(C{O_2}\), 3 NADH, and 1 \(FAD{H_2}\). 32 ATP molecules are generated during oxidative phosphorylation and ETC.

Frequently Asked Questions

1.How do electron carriers function?,
Ans. The metabolite is present at one end and oxygen is at the other end, therefore the electrons are carried by a series of proteins.

2. What are the processes in the conversion of glucose to pyruvate that require energy?
Ans. By using enzymes in intermediary processes, glyceraldehyde 3-phosphate and dihydroxyacetone phosphate are produced from glucose. These processes call for energy.

3. What is oxidative phosphorylation?
Ans. Oxidative phosphorylation, which takes place in the mitochondria, is the addition of the phosphate group through reactions that use the energy produced when ATP is made from ADP.

4. What is the importance of cellular respiration in living organisms?
Ans. Energy is released during cellular respiration, which activates a number of bodily processes. Therefore, ensuring the survival of living things is important.

Introduction

All living things require energy to carry out their many tasks, such as breathing, growth, metabolism, and movement. Because of this, cells need a constant flow of energy to support their development, maintenance, and repair. Although the sun is a good source of energy, not all types of life can use it directly. The process by which all the cells in living things produce energy is called cellular respiration. The body receives energy via the breakdown of glucose, whether oxygen is present or not.

What is Aerobic Respiration?

During aerobic respiration, glucose present in the food is converted into water and \(C{O_2}\). It releases energy in the form of ATP (Adenosine triphosphate) and each ATP hydrolysis gives 7.3 kcal/mol. Through this catabolic process, food is converted into energy that is needed for various body functions. Eukaryotes, prokaryotes, and plants undergo this process. The process is also known as oxidative metabolism.

Aerobic Respiration Equation 

When glucose is completely burned, carbon dioxide and water are released with energy as a byproduct. The overall equation of aerobic respiration is given here,

\[{{\bf{C}}_6}{{\bf{H}}_{12}}{{\bf{O}}_6}\left( {{\bf{Glucose}}} \right) + {\bf{6}}{{\bf{O}}_2}({\bf{Oxygen}}){\bf{6C}}{{\bf{O}}_2}\left( {{\bf{Carbon}}{\rm{ }}{\bf{dioxide}}} \right) + {\bf{6}}{{\bf{H}}_2}{\bf{O}}\left( {{\bf{Water}}} \right) + {\bf{Energy}}\]

About 2900 kJ are released and transformed into ATP, which is used for several purposes.

Steps Involved in Aerobic Respiration

The process of aerobic respiration involves four major steps with intermediate reactions. Those are as follows.

Glycolysis

Initially, glycolysis was derived from the Greek words glyco (meaning sugar or sweet) and lysis (meaning dissolution). As a universal sequential reaction, it occurs in both aerobic and anaerobic respiration in the cytosol of a cell.

• Two ATP molecules and two NADH molecules are produced when one glucose (glycogen) molecule breaks down into two molecules of three carbon compounds pyruvates.
• NADH (NAD+H) is the reduced form of NAD (nicotinamide adenine dinucleotide), which is the electron acceptor. The further process of aerobic respiration is carried out by these molecules. 
• Glycolysis is also called the “Embden- Meyerhof-Parnas” (EMP) Pathway.

Pyruvate oxidation (linking reaction)

• During this linking reaction, two stages are connected so that the end product of glycolysis can be used in the citric acid cycle.
• The enzyme pyruvate translocase assists in the entry of the two pyruvate molecules into the mitochondrial matrix. 
• Acetyl-CoA is formed by the oxidation of pyruvate by the Pyruvate dehydrogenase complex.

Citric acid/Krebs cycle

• Citric acid is produced by combining Acetyl-CoA with four-carbon oxaloacetate.
• ATP and carbon dioxide are produced sequentially, along with NADH and FADH reduced forms.
• It is also known as the TCA cycle (tricarboxylic acid cycle) because citric acid has three carboxyl groups.

Electron Transport Chain (ETC)

• This last stage of aerobic respiration occurs in the mitochondria. 
• ETC is a cluster of proteins that transports electrons across a membrane into mitochondria and generates a significant amount of ATP.
• One glucose molecule is broken down into 32 molecules of ATP during this aerobic respiration process.

Examples of Aerobic Respiration

• All multicellular species, including humans, birds, animals, and insects, partake in aerobic respiration. The glucose in the food breaks down in the presence of oxygen and releases energy. 
• It occurs in the majority of higher plants also.

Do all human cells carry out aerobic respiration?

All the cells in the human body are capable of doing aerobic respiration. However, during intense physical activity such as running, jogging, jumping rope, aerobic dance, and cycling up hills, where low oxygen levels result in low energy levels in the body, muscle cells can do anaerobic respiration. To obtain energy, the muscle cells resort to anaerobic respiration.

Aerobic Respiration in Plants

• In the cytosol and mitochondria of plant cells, aerobic respiration takes place.
• Oxygen and simple carbohydrates such as glucose function as reactants. 
• The stomata, which are pores in the epidermis of a plant’s stem and leaves, allow oxygen to enter the plant while it is engaged in aerobic respiration. 
• With the assistance of ambient oxygen, glucose completely breaks down to produce carbon dioxide and water. 
• Additionally, a significant amount of energy is released in the form of ATP.

Significance of Aerobic Respiration

• Living things require ATP that is produced during aerobic respiration to participate in metabolic processes and perform necessary bodily functions.
• Carbon dioxide, the by-product of aerobic respiration, can be used for photosynthesis in green plants. 
• Water, carbon dioxide, and sunlight can be combined during photosynthesis to produce food for plants. 
• Cell division also uses the energy that is generated during respiration.
• The intermediate compounds, organic acids, and coenzymes are useful for organic activities.

Summary

During aerobic respiration, glucose present in the food is converted into water and \(C{O_2}\). When glucose is completely burned, carbon dioxide and water are released as by-products along with energy. The process of aerobic respiration involves four major steps with intermediate reactions. Those are glycolysis, pyruvate oxidation, Krebs’s cycle, and the electron transport chain. In the cytosol and mitochondria of plant cells, aerobic respiration takes place.  Carbon dioxide, the by-product of aerobic respiration, can be used for photosynthesis in green plants.

Frequently Asked Questions

1. Which respiration process transforms glucose into energy more efficiently, and why?
Ans. The 36 ATP molecules are produced by aerobic cell respiration. The efficiency of aerobic cell respiration is about 18 times greater than that of anaerobic cell respiration. Due to the entire conversion of glucose into \(C{O_2}\) and energy, there is a significant amount of energy production.

2. What are ATP and NADH?
Ans. Adenosine triphosphate, or ATP, is an energy-carrying molecule that fuels the metabolism of living things. Nicotinamide adenine dinucleotide, or NAD, is an electron acceptor; its reduced version is called NADH.

3. What is the difference between breathing and cellular respiration?
Ans. While cellular respiration is a process of obtaining energy to carry out various bodily tasks, breathing is a process of exchanging gases between the environment and an organism.

4. Does anaerobic respiration takes place in the human cells?
Ans.  During heavy workouts, anaerobic respiration takes place in the muscles. Since there is no complete breakdown of glucose in anaerobic respiration, the energy liberated is less than that of aerobic respiration. The muscles accumulate lactic acid when you exercise vigorously. Then, this lactic acid oxidizes to produce water and \(C{O_2}\).

5. Where does oxygen-assisted respiration occur within the cell?
Ans. The cytoplasm of the cell serves as the starting point for aerobic respiration, which concludes in the mitochondria. The mitochondria are where the majority of aerobic respiration’s reactions take place.