9/25/25 Energy Production and Glycolysis

Enzymes: Function, Factors, and Regulation

• Controlled Energy Release: Cells avoid a single burst of energy release (like an explosion) by controlling the rate at which energy is extracted from molecules. This ensures that energy can be utilized effectively rather than harming the cell.

• Role of Enzymes: Enzymes are crucial proteins that regulate the rate of chemical reactions in cells. They facilitate reactions, either breaking molecules apart or joining them together. This depends on factors like the protein's function, enzyme concentration, and substrate availability.

• Active Site: The enzyme (e.g., in blue) binds to a substrate (e.g., yellow) at its active site, facilitating a chemical reaction.

• Factors Affecting Enzyme Function:

  • Temperature: Enzymes have an optimal temperature range. For humans, this is around $40 ext{ degrees Celsius}$. In prokaryotic archaea, it can be higher, around $70 ext{ degrees Celsius}$. Extreme temperatures (too hot or too cold) can change an enzyme's shape, leading to a loss of function.

  • pH: Enzymes also have an optimal pH. For example, pepsin (in the stomach) works best at a pH of around $2.5$, while trypsin works best at around $6.5$. Deviations from the optimal pH can alter an enzyme's shape, reducing its efficiency.

• Enzyme Recycling: Enzymes are recycled; they perform their job and can be reused multiple times. This is energy-efficient, as making new enzymes requires significant energy.

• Enzyme Inhibition:

  • Competitive Inhibition: An inhibitor molecule physically blocks the enzyme's active site, competing with the substrate and preventing the enzyme from performing its function. This is a way for the body to turn off an enzyme if there's an excess of its product.

  • Noncompetitive Inhibition: An inhibitor binds to a site on the enzyme other than the active site. This binding changes the enzyme's overall shape, including the active site's conformation, making it unable to bind to its substrate effectively.

• Biochemical Pathways & Feedback Inhibition:

  • Pathways: A series of sequential reactions, often catalyzed by multiple enzymes arranged in a row (e.g., on a cell membrane, Golgi apparatus, or endoplasmic reticulum). An initial molecule is transformed by Enzyme 1, then the product moves to Enzyme 2, and so on, until a final product is formed.

  • Feedback Inhibition: A regulatory mechanism where the end product of a biochemical pathway cycles back and deactivates an enzyme earlier in the pathway (often the first enzyme). This stops further production of the end product once sufficient quantities have accumulated, preventing waste.

• Enzyme Co-factors and Co-enzymes: These are molecules that help activate or facilitate enzyme function.

  • Cofactors: Often inorganic metals (e.g., magnesium, lithium, potassium) required in certain concentrations.

  • Coenzymes: Organic molecules (e.g., coenzyme Q, commonly found in multivitamins) that assist in reactions, often by moving electrons around. A balanced diet is important to obtain these molecules.

Metabolism: Anabolic vs. Catabolic Reactions

• Metabolism: The sum of all chemical reactions occurring within an organism.

• Anabolic Reactions: These reactions expend energy to build up complex molecules from simpler ones. An example is the process of muscle growth influenced by anabolic steroids, which builds up tissue and proteins.

• Catabolic Reactions: These reactions harvest energy by breaking down complex molecules into simpler ones. Cellular respiration is a prime example, where sugar is broken down to release energy.

• Organisms constantly perform both anabolic and catabolic reactions.

Adenosine Triphosphate (ATP): The Cell's Energy Currency

• ATP Structure: ATP (Adenosine Triphosphate) is the primary energy currency of the cell, providing energy for cellular reactions. It is a nucleic acid, built from:

  • A ribose sugar.

  • An adenine base.

  • Three phosphate groups.

• Related Molecules:

  • AMP (Adenosine Monophosphate): Contains one phosphate group.

  • ADP (Adenosine Diphosphate): Contains two phosphate groups.

  • ATP (Adenosine Triphosphate): Contains three phosphate groups.

• High-Energy Bonds: The bonds between the phosphate groups, particularly the terminal two, are considered