Glycolysis in Aerobic and Anaerobic Cells

 A metabolic route and anaerobic energy source known as glycolysis has evolved in almost all sorts of organisms. The Embden-Meyerhof pathway is another name for the process, given in honor of those who made significant contributions to its discovery and understanding. It has a purpose in anaerobic respiration and is the initial stage of cellular respiration, despite the fact that it doesn't need oxygen. As the most important organic fuel for plants, microorganisms, and animals, glucose molecules must be oxidized during the process. The majority of cells favor glucose, while there are some exceptions, including acetic acid bacteria, which prefer ethanol. In glycolysis, each glucose molecule yields 4 ATP, 2 NADH, and 2 pyruvates after the consumption of 2 ATP molecules. 

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What is Glycolysis?   

Splitting of 6-carbon compound glucose to form two products depending upon the process occurs aerobically and anaerobically.2 Pyruvates and 7ATPs are formed as a result of aerobic glycolysis. 2 Lactates and 2 ATPs are formed  as a result of anaerobic glycolysis. Glycolysis - Products Every glucose molecule generates

Through Aerobic glycolysis 2 Pyruvates and 7 ATPs and through Anaerobic glycolysis 2 Lactate and 2 ATPs.

Significance of Glycolysis is Glycolysis is the only pathway that generates ATPs even in the absence of oxygen.

Glycolysis - Cells Dependent     

Physiologically, the following cells are dependent on glycolysis for ATP production as they lack mitochondria. that is RBCs. Retinal cells and Corneal cells, White muscle fibres due to Lack of fresh blood supply during isometric contractions. In isometric contractions, the muscle length should be maintained constant during contraction between two fixed points. The tone of the muscle increases enormously. Any blood vessel entering the muscle gets constricted due to muscular contraction. They won't get a fresh supply of oxygen, nor does it have myoglobin. Thus, they depend on anaerobic glycolysis. Lack of myoglobin (Storage form of oxygen)

Renal medulla- In Ischaemic or hypoxic damage to the kidney, the renal medulla is affected the most as it receives blood from end arteries Receives very less blood supply necessary for Concentrating the urine and Maintaining interstitial medullary hyperosmolarity.

Preferred Fuels  for Glycolysis

• Preferred fuel for Anaerobic cells: Glucose
• Preferred fuel for Aerobic cells: They use both glucose and fatty acid. But fatty Acids over glucose, as fatty acids produce more ATPs.
• Examples of aerobic cells
  • Cardiac muscle fibres.
  • Red muscle fibres
• Examples of fatty acids
  • Palmitic acid: it Generates 106 ATPs.
  • Stearic acid: it  Generates 120 ATPs.

Exception: Neuron Cells - They  use glucose aerobically it uses Glucose for ATP production. Any fatty acids (nonpolar) present in the blood are conjugated with albumin to make them soluble. Fatty acids conjugated with albumin cannot penetrate BBB.

Difference of Glycolysis in Anaerobic Cells (RBCs) and Aerobic Cells (Neurons)

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What are the Steps of Glycolysis?

Step-01: Conversion of Glucose into  Glucose 6 Phosphate.

Glucose enters the cell. First enzyme to act on is Glucokinase or Hexokinase. This enzyme utilizes 1 high-energy phosphate (ATP) for conversion. Purpose of Step 01 is To trap glucose and to trans pass the GLUT transporters, as they can cause efflux glucose out to the circulation due to an increase in glucose concentration inside the cell. All GLUT transporters belong to Facilitated Passive Diffusion.

Step-02: Conversion of Glucose 6 Phosphate (G6P) into  Fructose 6 Phosphate (F6P).

G6P and F6P,Both have phosphate groups and are hexoses and isomers. and they are Interconvertible. Phosphate Hexose Isomerase enzyme is involved.

Step-03: Conversion of  Fructose 6 Phosphate (F6P) into  Fructose 1,6 bisphosphate.

Phosphofructokinase I use one ATP for the conversion. Steps 01 to 03 are named the investment phase because 2 ATPs are utilized. Further steps are considered as the Harvest phase (ATPs are generated).

Step-04:  Conversion of Fructose 1,6 bisphosphate → Glyceraldehyde 3 Phosphate + Dihydroxyacetone Phosphate.

This reaction yields two different trioses. Aldolase A mediates the reaction and is important in glucose glycolysis. Aldolase B is important in fructose glycolysis.

Step-05: Conversion of  Glyceraldehyde 3 Phosphate into Dihydroxyacetone Phosphate.

G3P and DHAP are Trioses and isomers. They are Interconvertible. Enzyme involved is PhosphoTriose Isomerase.

Step-06: Conversion of  2 (Glyceraldehyde 3 Phosphate) into  2 (1,3 bisphosphoglycerate.) 

Glyceraldehyde 3 Phosphate dehydrogenase enzyme is involved. This reaction is an example of oxidative phosphorylation.it Gives two hydrogens to NAD to form 2 NAD → 2 NADH. Each NADH enters the ETC and gets oxidized to give 2.5 ATPs. 2 NADH × 2.5 ATP = 5 ATPs.

Step-07: Conversion of 2 (1,3 Bisphosphoglycerate) into 2 (3-Phosphoglycerate.)

An example of substrate-level phosphorylation. Enzyme  used is  Phosphoglycerate kinase. In this process 2 ATPs are generated directly.

Step-08: Conversion of 2 (3-Phosphoglycerate) into 2 (2-Phosphoglycerate).

Positional isomerism is seen in the phosphate group of the above compounds.Mutases always mediate this type of isomerism.Enzyme used in this process is  Phosphoglycerate mutase.

Step-09: Conversion of  2 (2-Phosphoglycerate) into  2 (Phosphoenolpyruvate).

In this process Enolase acts by removing a water molecule.

Step-10: Conversion of  2 (Phosphoenolpyruvate) into  2 (Pyruvate).

It is Catalyzed by pyruvate kinase.it is An example of substrate-level phosphorylation. In this process 2 ATPs are generated directly.

In this process Total ATPs generated is  9. a Total of 2 ATPs invested so the Net ATP generated is  7.

Facts About Glycolysis        

• Aerobic glycolysis leads to production of 2 Pyruvates and 7 ATPs. Anaerobic glycolysis leads to production of  2 Lactate and 2 ATPs. The Hexokinase or Glucokinase step traps the glucose inside the cell. Irreversible steps of glycolysis, marking them can make gluconeogenesis (Reversal of Glycolysis) easy.
  • Hexokinase or Glucokinase
  • Phosphofructokinase I (rate-limiting step of glycolysis)
  • Pyruvate Kinase
• Substrate level phosphorylation steps are catalyzed by phosphoglycerate kinase and pyruvate kinase enzymes. 
• Oxidative phosphorylation step is catalyzed by glyceraldehyde 3 phosphate dehydrogenase.
• Lactate is formed in anaerobic glycolysis for the regeneration of NAD. 

Hexokinase and Glucokinase

Glucokinase is present in the liver cells and beta cells of the pancreas and exhibits low affinity because. Liver is the 1st organ to meet dietary glucose. If it has a higher affinity, it may consume all for itself, and this may cause the peripheral tissues to suffer from hypoglycemia. Glucose enters the pancreatic beta cells and goes through glycolysis and then to the TCA Cycle. The cell gets the ATP and closes ATP-sensitive potassium channels. This causes depolarisation and action potential, causing the release of insulin.

If pancreatic beta cells were provided with more glucose, they'll release more insulin that may cause hypoglycemia.

Km and Affinity    

Km stands for Michaelis Constant,

Km = [S - Substrate concentration] at ½ maximal velocity (Vmax).

When the enzyme affinity for the substrate is low, more substrate is given to achieve the ½ maximal velocity. Example.

If Km = 100 µ mol, then [S] = 100 µ mol. and If Km = 200 µ mol, then [S] = 200 µ mol. Km is inversely proportional to Affinity.

What are the Inhibitors of Glycolysis?

Sodium fluoride + potassium oxalate (anticoagulant) comes in a gray top tube and is used for plasma glucose estimation. To avoid false glucose estimation as there will be a window period (1 and a half - 2 hours) between sample collection and sample analysis.

Facts About Rapaport Leubering Shunt or 2,3 BPG Shunt              

Phosphoglycerate kinase converts 2(1,3 BPG) is converted to 2(3 PG) usually we get 2 ATPs. In RBC, it needs 2,3 BPG. It helps in unloading O2 to tissues. It bypasses the phosphoglycerate kinase step to deliver oxygen to the tissues by decreasing the affinity of haemoglobin. 2(1,3 BPG) is converted to 2(2,3 BPG) (positional isomerism) catalyzed by Bis Phosphoglycerate mutase, and this molecule is useful in delivering oxygen. 2(2,3 BPG) is converted into 2 (3-PG) mediated by bisphosphoglycerate phosphatase. 2(3-PG) finally gets converted into 2 (2-PG) via phosphoglycerate mutase. It Acts as a source of 2,3-BPG. but there is Zero ATP production.

This is everything that you need to know about Glycolysis for your biochemistry preparation. For more interesting and informative blog posts like this download the PrepLadder App and keep reading our blog!