Biochemical Processes and Enzyme Regulation

Digestion and Metabolism

• Order of Processes

  • Digestion comes first in the metabolic pathway.

  • Breaking down larger molecules into smaller ones for absorption into the bloodstream.

  • Small molecules are then converted to acetyl CoA for further metabolic processes.

• Digestion Details

  • Initial breakdown takes place during chewing; ideally, food should be chewed approximately 32 times.

  • Types of food involved:

  • Carbohydrates

  • Triglycerides (Fats)

  • All foods enter the stomach where proteins are denatured and amino acids are separated for further breakdown.

• Small Intestine Role

  • The small intestine is crucial for the final breakdown of carbohydrates and fats, allowing them to be absorbed into the bloodstream.

  • All processed food is ultimately converted to acetyl CoA, which serves as the primary currency for the citric acid cycle.

Citric Acid Cycle (Krebs Cycle)

• Function of Acetyl CoA

  • Acetyl CoA undergoes oxidation in the Krebs cycle.

  • During this process, electrons are removed from acetyl CoA which then leads to the production of reduced coenzymes, specifically NADH and FADH₂.

  • These coenzymes serve as electron carriers to the electron transport chain (ETC).

• Energy Conversion

  • The main purpose of the citric acid cycle is to convert light energy (from plants) into chemical energy in the form of electron energy, ultimately leading to the production of ATP.

  • As chemical energy is oxidized, it produces carbon dioxide (CO₂) and water (H₂O) as waste products.

Electron Transport Chain (ETC)

• Mechanism

  • The ETC occurs in the mitochondria, where NADH and FADH₂ donate the electrons.

  • This transfer creates an electrochemical gradient across the membrane.

  • Protons are concentrated on one side of the membrane, creating a gradient akin to blocking a creek to build up water behind a dam.

  • When protons rush back through, they drive cellular processes such as converting ADP to ATP, releasing energy through the generation of ATP.

• Importance of Oxygen

  • Oxygen acts as the final electron acceptor, stopping the electrons' movement in the chain and preventing heat production through uncontrolled electron flow.

  • Approximately 90% of oxygen inhaled is used to support these oxidative processes.

Glycolysis

• Location: Glycolysis occurs in the cytosol (the fluid component of the cytoplasm).

• Function: Glycolysis is a primary pathway for converting glucose to acetyl CoA, which is essential for producing energy in the form of ATP.

Enzymes and Metabolism

• Role of Enzymes

  • Enzymes serve as biological catalysts facilitating chemical reactions.

  • They specifically lower the activation energy required for reactions to occur, akin to taking an elevator instead of walking up stairs.

• Activation Energy

  • Activation energy is the energy required to start a chemical reaction.

  • Enzymes remove barriers to reactions, allowing them to occur more efficiently.

• Specificity and Function

  • Enzymes exhibit specificity, usually acting on one substrate to produce a product.

  • Classification of enzymes includes catalysis types depending on their mechanisms in reactions, such as hydrolysis.

Enzyme Mechanism: Induced Fit Model

• Substrate Binding

  • The induced fit model indicates that enzyme conformation changes upon substrate binding, optimizing interactions between enzyme and substrate.

  • The enzyme undergoes a change that helps facilitate the formation of the product more effectively.

Regulation of Enzymatic Activity

• Types of Inhibition

  • Competitive Inhibition: Inhibitors bind to the active sites of enzymes, blocking substrate binding.

  • Increased substrate concentration can outcompete the inhibitor for active sites.

  • Non-competitive Inhibition: Inhibitors bind to sites other than the active site, altering enzyme shape and function. Cannot be outcompeted by substrate.

• Allosteric Regulation

  • Allosteric inhibitors bind to alternative sites and distort the enzyme's active site, preventing substrate binding.

  • They represent a method for regulating enzyme activity without competing with substrates for the active site.

  • Allosteric activators enhance enzyme activity, possibly altering enzyme shape to facilitate substrate binding more efficiently.

• Feedback Inhibition

  • Feedback inhibition allows the cell to regulate metabolic pathways based on product levels. If too much product accumulates, it can inhibit the first enzyme in the pathway, halting further production.

Conclusion

• Understanding these metabolic processes and enzymatic functions is crucial for grasping biological energy cycles and chemical pathways in cellular biology. Each stage, from digestion to ATP production, illustrates how life harnesses energy and regulates its chemical activities efficiently.