Chapter Summaries and Key Points

Section 3.2: ATP - Energy Currency of the Cell

Key Concepts:

1. ATP’s Role in Cellular Work:

   • ATP (Adenosine Triphosphate) supplies energy for cellular functions like DNA synthesis, protein synthesis, and muscle contractions. It’s known as the “energy currency” due to its universal role across all organisms.

   • Types of work by ATP include mechanical (e.g., muscle contractions), transport (e.g., active transport across membranes), and chemical (e.g., protein synthesis).

2. ATP Hydrolysis and Free Energy:

   • Hydrolysis of ATP (breaking a phosphate bond) releases energy, converting ATP to ADP and inorganic phosphate (ΔG=−30.5 kJ/mol\Delta G = -30.5 \, kJ/molΔG=−30.5kJ/mol).

   • This process releases energy used in endergonic (energy-requiring) reactions through energy coupling.

3. ATP Cycle:

   • ATP is continuously regenerated from ADP and inorganic phosphate, requiring energy input from food molecules.

   • Cycle Purpose: To efficiently harness energy and avoid dependence on glucose or other specific molecules alone.

Key Questions to Review:

• Question 3: Structure of ATP, with an emphasis on how the phosphate bonds store energy.

• Question 4: ATP hydrolysis and energy release.

• Question 12: Advantage of ATP as an energy source over direct use of glucose or lipids.

Section 3.3: Enzymes and Activation Energy

Key Concepts:

1. Role of Enzymes:

   • Enzymes speed up reactions by lowering activation energy (Ea), allowing cellular reactions to proceed faster.

   • Enzymes do not affect the overall ∆G of reactions, only the energy pathway.

2. Mechanisms of Enzyme Action:

   • Mechanisms include bringing substrates close together, altering charge environments, and bending substrates to weaken bonds (induced-fit model).

   • Enzymes are sensitive to environmental conditions; high temperatures, for example, can denature them.

3. Activation Energy and Reaction Rate:

   • Activation energy is required to initiate reactions. For instance, the hydrolysis of sucrose is exergonic but needs an enzyme to proceed efficiently at biological temperatures.

Key Questions to Review:

• Question 2: Why some spontaneous reactions do not occur immediately.

• Question 4: Draw and explain enzyme effects on activation energy graphs for exergonic and endergonic reactions.

• Question 6: Three main mechanisms by which enzymes lower activation energy.

Section 3.4: Food as Fuel

Key Concepts:

1. Energy in Fuels:

   • Glucose and fats are high-energy molecules because of C–H bonds, which store potential energy.

   • Oxidation-Reduction (Redox) Reactions are central to cellular respiration, involving the transfer of electrons (e.g., glucose oxidation in cells).

2. Controlled Oxidation:

   • Controlled oxidation in cells (e.g., glucose breakdown) occurs in multiple steps, releasing energy gradually and efficiently, unlike rapid combustion.

3. NAD+ as an Electron Carrier:

   • NAD+ accepts electrons (becoming NADH), which temporarily stores energy for later ATP synthesis.

Key Questions to Review:

• Question 2 (a-c): Write the equation for glucose combustion, identifying oxidizing and reducing agents.

• Question 3: Energy release due to electron positioning changes in redox reactions.

• Question 9: Benefits of controlled oxidation over rapid combustion.