Metabolism, Anabolism, ATP, and Enzymes

Metabolism is the total set of chemical reactions occurring in a cell, enabling growth, maintenance, and response to the environment.
Reactions are organized into pathways; energy is captured, stored, and used to drive work.
Metabolism includes both anabolic (building up) and catabolic (breaking down) processes.
Understanding metabolism helps connect energy flow to biosynthesis and cellular function.

The lecture emphasizes understanding metabolism and differentiating between anabolism and metabolism. Note: Anabolism is a subset of metabolism; metabolism encompasses both anabolic and catabolic processes.
Anabolism (biosynthesis): building complex molecules from simpler ones; examples include protein synthesis, nucleotide synthesis, lipid synthesis; typically requires energy input.
Catabolism (energy-releasing): breakdown of larger molecules into simpler ones, releasing energy that can be harvested to form ATP.
Key idea: ATP acts as a key energy currency that couples energy-releasing (catabolic) processes to energy-requiring (anabolic) processes.

ATP serves as the primary energy currency in cells.
Functions of ATP:
- Powers mechanical work (e.g., muscle contraction and motor proteins).
- Drives active transport across membranes.
- Drives biosynthetic and other endergonic reactions.
ATP hydrolysis reaction: $\mathrm{ATP} + \mathrm{H<em>2O} \rightarrow \mathrm{ADP} + \mathrm{P</em>i}$
- Standard free energy change: $\Delta G^{\circ\prime} \approx -30.5\ \text{kJ/mol}$
- Under cellular conditions, the effective free energy change can be more negative (often around -50 to -60 kJ/mol depending on conditions).
ATP cycling and coupling: energy released from ATP hydrolysis is used to drive endergonic reactions by coupling.

Enzymes are biological catalysts that accelerate chemical reactions without being consumed.
Key features:
- Specificity: each enzyme acts on particular substrates at an active site.
- Mechanism: lower the activation energy ((\Delta G^{\ddagger})) needed for a reaction to proceed.
- Do not alter the overall thermodynamics ((\Delta G)) of the reaction; they speed up the rate.
- Formation and breakdown of the enzyme–substrate complex (ES) release product.
Regulation and cofactors:
- Enzyme activity can be regulated by activators, inhibitors, phosphorylation, etc.
- Cofactors and coenzymes (e.g., metal ions, NAD^+, FAD) assist catalysis or substrate binding.
Factors affecting enzyme activity:
- Temperature and pH: deviations from optimum reduce activity or denature the enzyme.
- Substrate concentration: affects rate until saturation.
- Presence of inhibitors/activators: modulate activity.
Activation energy concept:
- Enzymes lower the activation energy of a reaction:
  $\Delta G^{\ddagger}<em>{\text{uncatalyzed}} > \Delta G^{\ddagger}</em>{\text{catalyzed}}$

Metabolism connects energy flow with biosynthesis and cellular function.
ATP as energy currency links energy release in catabolism to energy consumption in anabolism; energy carriers like NADH and FADH2 also play roles in transferring energy.
Enzymes enable precise control of metabolic pathways, enabling regulation, speed, and efficiency in cellular processes.

The instructor announced that the next topic will cover photosynthesis and cellular respiration.
These topics are described as tricky and hard to study in isolation; attendance is encouraged.
The content builds on the metabolism and enzyme concepts discussed today and provides foundational understanding of energy capture and conversion in biology.

Day’s objectives recap:
- Understand metabolism and differentiate between anabolism and metabolism.
- Discuss ATP: its functions and importance.
- Discuss enzymes and what they do.
These objectives are presented in a day-by-day study-guide format to facilitate learning.
Practical advice: make sure not to miss the lecture and use study guides to reinforce understanding.