What is Respiration?
Respiration is a process that occurs in all living beings in which oxygen is utilised and carbon dioxide is released from the body. The mechanism of cellular respiration involves the following mechanism:
Glycolysis
Anaerobic Breakdown of Pyruvic acid
Krebs Cycle
Electron Transport system
Terminal oxidation and oxidative phosphorylation
Pentose phosphate pathway
Here, in the article, let us discuss the difference between the Krebs Cycle and glycolysis but first let us take a look at what each of these terms means.
Glycolysis – It is an anaerobic process in which a molecule of glucose is converted into two molecules of pyruvic acid. It takes place in the cytoplasm
Krebs Cycle – It is an aerobic process that takes place in the mitochondria that involves the oxidation of pyruvic acid into water and carbon dioxide.
Given below in a tabular column are the differences between glycolysis and Krebs Cycle.
Differences Between Glycolysis and Krebs Cycle
Both glycolysis and Krebs are enzymes medicated and are under constant regulation based on the energy requirements of cells/organisms. The rates of these processes vary under various conditions such as the well-fed state, fasting state, exercised state, and starvation state.
The Krebs cycle or Citric acid cycle is a series of enzyme catalysed reactions occurring in the mitochondrial matrix, where acetyl-CoA is oxidised to form carbon dioxide and coenzymes are reduced, which generate ATP in the electron transport chain.
Krebs cycle was named after Hans Krebs, who postulated the detailed cycle. He was awarded the Nobel prize in 1953 for his contribution.
It is a series of eight-step processes, where the acetyl group of acetyl-CoA is oxidised to form two molecules of CO2 and in the process, one ATP is produced. Reduced high-energy compounds, NADH, and FADH2 are also produced.
Two molecules of acetyl-CoA are produced from each glucose molecule, so two turns of the Krebs cycle are required which yields four CO2, six NADH, two FADH2, and two ATPs.
Krebs cycle can be defined as an eight-step process occurring in the mitochondrial matrix. Acetyl CoA, derived from carbohydrates, proteins, and fats, is completely oxidised to release carbon dioxide. In the form of ATP, the energy released is stored. The eight steps involved are as follows:
Step 1: The first step is the condensation of acetyl CoA with oxaloacetate (4C) to form citrate (6C), coenzyme A is released. The reaction is catalysed by citrate synthase.
Step 2: Citrate is turned to its isomer, isocitrate. The enzyme aconitase catalyses this reaction.
Step 3: Isocitrate undergoes dehydrogenation and decarboxylation to form 𝝰-ketoglutarate (5C). A molecule of CO2 is released. Isocitrate dehydrogenase catalyzes the reaction. It is an NADh-dependent enzyme. NAD+ is converted to NADH.
Step 4: 𝝰-ketoglutarate (5C) undergoes oxidative decarboxylation to form succinyl CoA (4C). The reaction is catalyzed by 𝝰-ketoglutarate dehydrogenase enzyme complex. One molecule of CO2 is released and NAD+ is converted to NADH.
Step 5: Succinyl CoA is converted to succinate by the enzyme succinyl CoA synthetase. This is coupled with substrate-level phosphorylation of GDP to form GTP. GTP transfers its phosphate to ADP forming ATP.
Step 6: Succinate is oxidised to fumarate by the enzyme succinate dehydrogenase. In the process, FAD is converted to FADH2.
Step 7: Fumarate gets converted to malate by the addition of one H2O. The enzyme catalysing this reaction is fumarase.
Step 8: Malate is dehydrogenated to form oxaloacetate, which combines with another molecule of acetyl CoA and starts the new cycle. Hydrogens removed get transferred to NAD+ forming NADH. Malate dehydrogenase catalyses the reaction.
FAQs on Difference Between Glycolysis and Krebs Cycle
1. Name the pathway that Gustav Embden, Otto Meyerhof, and J. Parnas identified?
The Embden–Meyerhof–Parnas (EMP) pathway was identified by Gustav Embden, Otto Meyerhof, and Jakub Karol Parnas and is the most prevalent kind of glycolysis.
The metabolic mechanism that transforms glucose into pyruvate is known as glycolysis. The cytoplasm is where this happens. In the process of cellular metabolism, it is the initial step in the breakdown of glucose to extract energy. The first phase in cellular respiration is known as glycolysis. Glycolysis is a process that involves splitting a six-carbon molecule, converting glucose into three-carbon molecules, and producing pyruvates.
2. What is pyruvate and how does it work?
Pyruvate is a biological substance and a result of glucose metabolism that combines with adenosine triphosphate and carbon dioxide at the start of the TCA cycle to produce acetyl-CoA and adenosine diphosphate (ADP). It is frequently included in the cycle's first or preparatory stage. Pyruvate is usually derived from the glycolysis product pyruvic acid, which in most natural systems quickly dissociates to leave pyruvate.
3. What is the other name for glycolysis?
The Embden–Meyerhof–Parnas (EMP) is another name of glycolysis discovered by Gustav Embden, Otto Meyerhof, and Jakub Karol Parnas. The metabolic mechanism that transforms glucose \[(C_{6}H_{12}O_{6})\] to pyruvic acid \[(CH_{3}COCOOH)\] is known as glycolysis. The high-energy molecules adenosine triphosphate (ATP) and reduced nicotinamide adenine dinucleotide are formed from the free energy released during this process (NADH).[1] Glycolysis is a set of ten enzyme-catalyzed processes.
4. Identify two processes in glycolysis where ATP is used.
1st Step: Hexokinase is an enzyme that phosphorylates or adds a phosphate group to glucose in the cytoplasm of a cell. A phosphate group from ATP is transferred to glucose throughout the process, resulting in glucose 6-phosphate, or G6P. During this phase, one molecule of ATP is consumed.
2nd Step: Phosphoglucomutase is an enzyme that converts G6P to its isomer fructose 6-phosphate, or F6P. Isomers share the same chemical formula but differ in their atomic configurations. When fructose-6-phosphate is phosphorylated into fructose-1,6-bisphosphate, the second molecule of ATP is utilized.
5. Define Krebs cycle.
The citric acid cycle links glucose, lipid, and protein metabolism. The cycle's processes are carried out by eight enzymes, each of which completely oxidizes acetate (a two-carbon molecule) in the form of acetyl-CoA into two carbon dioxide and water molecules. The two-carbon organic product acetyl-CoA is formed through the catabolism of carbohydrates, lipids, and proteins, and it enters the citric acid cycle. The tricarboxylic acid (TCA) cycle, commonly known as the Krebs cycle, also known as the citric acid cycle, is a vital aspect of aerobic respiration and the primary source of energy for cells.
