In-Depth Notes on Biology 120

Energy and Enzymes

• Enzymes: Essential for catalyzing metabolic reactions in cells.

• Influence of Physical Conditions: Enzyme activity can be affected by various factors, including temperature, pH, and concentration of substrates.

Types of Energy

• Potential Energy: Stored energy based on position (e.g., concentration gradients).

• Chemical Energy: Stored in molecular bonds (e.g., ATP, glucose).

• Kinetic Energy: Energy of movement (e.g., flagella in bacteria).

• Thermal Energy: Energy from the movement of molecules, correlated to temperature.

• Light Energy: From the sun, utilized by plants during photosynthesis.

• Electrical Energy: Movement of charged particles (e.g., Na+/K+ ions).

• Mechanical Energy: Direct physical movement or force (e.g., beating of cilia).

Laws of Thermodynamics

1. First Law: Energy cannot be created or destroyed, only transformed.

   • Example: Chemical energy in glucose is converted to ATP + heat.

2. Second Law: Energy transfers increase entropy (disorder).

   • Example: Breakdown of glucose releases energy and heat, increasing disorder.

3. Third Law: As temperature approaches absolute zero, molecular motion stops, and entropy approaches zero.

Energy Exchange in Systems

• Isolated System: Exchanges neither energy nor matter with surroundings.

• Open System: Exchanges both energy and matter.

• Closed System: Exchanges energy but not matter.

Spontaneity of Reactions

• Free Energy Change (ΔG): Determines whether a reaction is spontaneous.

  • Formula: $ext{ΔG} = ext{ΔH} - T ext{ΔS}$

  • ΔG < 0: Spontaneous (exergonic)

  • ΔG > 0: Non-spontaneous (endergonic)

Enthalpy and Entropy Change

• Enthalpy (ΔH): Change in heat energy.

  • ΔH < 0: Exothermic (releases energy, favors spontaneity).

  • ΔH > 0: Endothermic (absorbs energy, less favorable).

• Entropy (ΔS): Change in disorder.

  • ΔS > 0: More disorder (favors spontaneity).

Types of Reactions

• Exergonic Reactions: Energy is released, spontaneous, ΔG < 0, linked to catabolism (e.g., cellular respiration).

• Endergonic Reactions: Energy is required, non-spontaneous, ΔG > 0, linked to anabolism (e.g., photosynthesis).

Catabolic vs. Anabolic Reactions

• Catabolic Reactions: Break down molecules; yield energy, produce ATP, spontaneous (e.g., digestion of proteins).

• Anabolic Reactions: Build complex molecules; require energy input, non-spontaneous (e.g., protein synthesis).

ATP Structure and Function

• ATP (Adenosine Triphosphate): Composed of adenine, ribose, and three phosphate groups.

• Bonds between phosphate groups store high energy; breaking the last bond releases energy.

ATP Hydrolysis

• Definition: Breaking down ATP using water, an exergonic reaction releasing energy.

• Reaction: $ext{ATP} + ext{H}_2 ext{O} <br>ightarrow ext{ADP} + ext{Pi} + ext{Energy}$

Coupled Reactions with ATP

• Definition: ATP hydrolysis powers endergonic reactions.

• Example: Glucose and inorganic phosphate become glucose-6-phosphate using ATP.

ATP Cycle

• Continuous ATP Production: ATP is constantly regenerated from ADP and inorganic phosphate.

• Importance: Links catabolic and anabolic processes, maintaining cellular energy flow.

Enzymatic Functionality

• Enzymes: Catalysts that speed up reactions without being consumed.

• Functions: Lower activation energy, increase reaction rates, and specificity.

• Examples: Amylase, DNA polymerase, ATP synthase.

Mechanisms of Action

• Enzymes hold substrates in optimal positions to react, modify pH, and provide co-factors (metals like Mg or Zn) to stabilize charges.

Factors Influencing Enzyme Activity

• pH: Extreme pH can denature enzymes.

• Temperature: Low temperature slows reactions, while high temperature may lead to denaturation.

Induced-fit Model

• More widely accepted model of enzyme-substrate interaction.

Cofactors and Enzymes

• Inorganic Cofactors: Metal ions like Mg, Zn, Fe.

• Organic Cofactors: Vitamins (e.g., NAD+, FAD, Coenzyme A).

Defining Life and Origins

• Challenges in Definition: Life varies from unicellular (bacteria) to multicellular (humans). Common attributes complicate a simple definition.

Seven Properties of Life

1. Display Order

2. Utilize Energy

3. Reproduce

4. Respond to Stimuli

5. Homeostasis

6. Growth and Development

7. Evolve

Viruses and Life

• Viruses lack essential characteristics of life; they lack ribosomes and metabolism, relying on host cells for replication.