AP BIO Unit 3 Lesson 2

ATP and Energy

  • ATP (Adenosine Triphosphate) is the primary energy carrier in living organisms.

  • The conversion between ATP and ADP (Adenosine Diphosphate) involves the addition or removal of a phosphate group.

  • Adding a phosphate group to ADP to form ATP is an endergonic process; it requires input of energy.

  • Breaking down ATP to ADP and inorganic phosphate releases a significant amount of energy due to the repulsion between the negatively charged phosphate groups.

Chemical Structure and Bond Interaction

  • Phosphates in ATP are negatively charged.

  • Negative charges repel each other, which results in a high-energy state when ATP is intact.

  • When the bond between the phosphates is broken, the repulsion energy is released as useful work.

Cellular Respiration

  • Cellular respiration is the process by which cells break down glucose and other macromolecules to release energy (exergonic reaction).

  • This released energy drives the endergonic process of re-phosphorylating ADP to form ATP.

  • Glucose is a quick energy source, glycogen and starch provide medium-term energy, and triglycerides offer long-term energy due to their high caloric content.

  • Oxygen is a necessary component for cellular respiration.

Energy Requirements and Usage

  • Continuous cellular respiration is essential for cellular functions, occurring 24/7.

  • Excess calories and oxygen allow for the recharging of ATP.

Energetics of Reactions

  • Some reactions, despite being exergonic (spontaneous), can be very slow due to activation energy barriers.

  • Example: Rusting of iron is an exergonic reaction that occurs at a slow rate.

Activation Energy

  • The energy required to reach the transition state in a reaction is known as activation energy.

  • A higher activation energy results in a slower reaction, while a lower activation energy allows for a faster reaction.

  • Enzymes lower the activation energy required for a reaction, facilitating rapid completion of biological processes.

Role of Enzymes

  • Enzymes serve as catalysts that increase the rate of reactions without being consumed.

  • They accelerate biochemical processes by reducing activation energy.

  • Enzymes do not add energy; they lower the threshold needed to initiate a reaction.

  • The enzyme must maintain its structure and integrity to function effectively.

Importance of Enzymes in Metabolic Pathways

  • Every step in a metabolic pathway typically requires an enzyme to ensure speed and efficiency.

  • Slow steps could halt the entire reaction sequence due to dependence on preceding reactions.

Regulation of Metabolic Pathways

Feedback Inhibition

  • Metabolic pathways can self-regulate through feedback inhibition, where the end product inhibits an enzyme early in the pathway.

  • If the end product concentration is high, it acts as an inhibitor, preventing unnecessary production.

Mechanism of Regulation

  • Consider a pathway converting substrate A to B, then C, D, and finally E to form product F.

  • Enzymatic activity is directly controlled by the concentration of the product F.

  • When product F concentration is high, it inhibits an early enzyme, shutting down the pathway.

  • If product F concentration falls, inhibition ceases, permitting the pathway to resume production.

Practical Implications

  • Searching for efficient energy usage in biological systems enhances adaptive advantages in evolutionary terms.

  • Organisms optimize their metabolism based on energy demands and resource availability.

Cellular Respiration Example

  • Cellular respiration is a critical example of metabolic pathway regulation where ATP levels serve as an indicator for the need to initiate or inhibit further energy extraction from glucose.

  • If ATP is abundant, cellular respiration slows down; if ATP levels drop due to increased energy demands (e.g. muscle contraction), respiration speeds up.