Intracellular and Extracellular Enzyme-Catalysed Reactions
- Enzymes are essential for metabolism, the sum of all chemical reactions in living organisms.
- These reactions can occur inside cells (intracellular) or outside cells (extracellular).
Definition
Intracellular enzymes
Intracellular enzymes operate within cells, driving critical metabolic pathways such as glycolysis and the Krebs cycle.
Definition
Extracellular enzymes
Extracellular enzymes work outside cells to break down large molecules into smaller, absorbable units.
Glycolysis: Breaking Down Glucose in the Cytoplasm
Definition
Glycolysis
Glycolysis is the first step in cellular respiration, where glucose is broken down into pyruvate, releasing energy in the form of ATP.
This process occurs in the cytoplasm and involves a series of enzyme-catalysed reactions.
1. Phosphorylation of Glucose:
- The enzyme hexokinase adds a phosphate group to glucose, forming glucose-6-phosphate.
- This step requires ATP and traps glucose in the cell, making it more reactive.
2. Conversion to Pyruvate:
- Through a series of steps, glucose is split into two three-carbon molecules called pyruvate.
- During this process, ATP and NADH(an electron carrier) are produced.
- Glycolysis is an anaerobic process, meaning it does not require oxygen.
- It is the first step in both aerobic and anaerobic respiration.
The Krebs Cycle: Energy Extraction in the Mitochondria
Definition
The Krebs cycle
The Krebs cycle (also known as the citric acid cycle) occurs in the mitochondrial matrix and is a key part of aerobic respiration.
- The Krebs cycle completes the breakdown of glucose by oxidizing acetyl-CoA (derived from pyruvate) into carbon dioxide.
- Formation of Citrate
- Acetyl-CoA combines with oxaloacetate to form citrate, catalysed by the enzyme citrate synthase.
- Energy Extraction
- The cycle involves a series of reactions that release energy.
- Formation of Citrate
