Glycolysis
Glycolysis is a fundamental metabolic pathway that occurs in the cytoplasm of cells and is an important part of cellular respiration. It involves the breakdown of glucose molecules into two molecules of pyruvate, along with the production of ATP (adenosine triphosphate) and NADH (nicotinamide adenine dinucleotide).
The overall reaction for glycolysis can be summarized as follows:
Glucose + 2 NAD+ + 2 ADP + 2 Pi → 2 pyruvate + 2 NADH + 2 ATP + 2 H2O
Let’s break down the process into its individual steps:
- Hexokinase/ Glucokinase: Glucose enters the cell and is phosphorylated by the enzyme hexokinase (in most tissues) or glucokinase (in the liver) to form glucose-6-phosphate (G6P).
- Phosphohexose isomerase: G6P is then converted to fructose-6-phosphate (F6P) through an isomerization reaction.
- Phosphofructokinase-1 (PFK-1): F6P is phosphorylated by ATP to form fructose-1,6-bisphosphate (F1,6BP) with the help of the enzyme PFK-1. This step is considered the committed step of glycolysis and is regulated to control the flux of glucose through the pathway.
- Aldolase: F1,6BP is cleaved into two three-carbon molecules: glyceraldehyde-3-phosphate (G3P) and dihydroxyacetone phosphate (DHAP).
- Triose phosphate isomerase: DHAP is converted into another molecule of G3P, which is an intermediate required for the continuation of glycolysis.
- Glyceraldehyde-3-phosphate dehydrogenase: G3P is oxidized by removing hydrogen atoms and transferring them to NAD+ to form NADH. This reaction also leads to the production of 1,3-bisphosphoglycerate (1,3BPG).
- Phosphoglycerate kinase: 1,3BPG donates a phosphate group to ADP, generating ATP and converting 1,3BPG into 3-phosphoglycerate (3PG).
- Phosphoglycerate mutase: 3PG is converted into 2-phosphoglycerate (2PG) by relocating the phosphate group.
- Enolase: 2PG loses water to form phosphoenolpyruvate (PEP).
- Pyruvate kinase: PEP transfers a phosphate group to ADP, forming ATP and generating pyruvate.
Overall, glycolysis produces a net gain of 2 ATP molecules through substrate-level phosphorylation (steps 7 and 10). Additionally, for every glucose molecule processed, there is a net production of 2 NADH molecules, which can be further used in the electron transport chain to generate more ATP.
It is important to note that the fate of pyruvate after glycolysis depends on oxygen availability and cellular conditions. In the absence of oxygen (anaerobic conditions), pyruvate can be converted into lactate (lactic acid fermentation) or ethanol (alcoholic fermentation). In the presence of oxygen (aerobic conditions), pyruvate can enter the mitochondria to undergo further oxidation in the citric acid cycle and oxidative phosphorylation to produce more ATP.
First Year Pharm D Subjects Syllabus, Notes, PDF Books, MCQ
| 1.1 | Human Anatomy and Physiology |
| 1.2 | Pharmaceutics |
| 1.3 | Medicinal Biochemistry |
| 1.4 | Pharmaceutical Organic Chemistry |
| 1.5 | Pharmaceutical Inorganic Chemistry |
| 1.6 | Remedial Mathematics/ Biology |
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