Chapter 6 Bio 201

Energy as a Fundamental Requirement for Life
- Life is defined by properties that require energy.
- Energy flow is essential for the functioning of living organisms.

Thermodynamics
- Study of energy changes in chemical systems.
- Organisms obey the laws of physics and chemistry.

Definition of Energy
- Capacity to do work.
- Two main states:
  - Kinetic Energy: Energy of motion.
  - Potential Energy: Stored energy that can enable motion.
- Forms of energy include mechanical, heat, sound, electric, light, and radioactivity.

Units of Energy
- Heat: Convenient measure of energy.
- Biological Unit: Kilocalorie (kcal).
  - 1 kcal = heat required to raise 1 kg of water by 1°C.
  - The calorie with a capital C on food labels refers to 1 kcal.
- Physics Unit: Joule (J).
  - 1 J = 0.239 cal.

Energy Capture
- Energy flows from the sun into the biological world.
- Photosynthetic organisms capture this energy, storing it in chemical bonds of molecules like sugars.
- Breaking chemical bonds requires energy, which can then be used to form new bonds.

Oxidation and Reduction
- Oxidation: Loss of an electron; occurs frequently with oxygen as the electron acceptor.
- Reduction: Gain of an electron.
- These processes are always paired in oxidation-reduction reactions (redox).

First Law of Thermodynamics
- Energy is conserved; it cannot be created or destroyed.
- Energy can change forms (e.g., from potential to kinetic).
- Total energy in the universe remains constant, but some is lost as heat during transformations.
Second Law of Thermodynamics
- Entropy (disorder) of the universe is increasing.
- Energy transformations are never 100% efficient; some energy becomes unavailable.
- Systems move toward less ordered states spontaneously.

Definition
- Free energy (G) is the energy available to perform work.
- Formula: G = H − TS
  - H = enthalpy (total energy), T = absolute temperature, S = entropy.
Change in Free Energy (ΔG)
- Positive ΔG indicates non-spontaneous reactions (endergonic), requiring energy input.
- Negative ΔG indicates spontaneous reactions (exergonic), releasing energy.

Activation Energy
- Extra energy is needed to destabilize bonds and initiate a chemical reaction.
- The rate of reaction is influenced by the activation energy needed.
- Reaction rates can be increased by raising the energy of reactants or lowering the activation energy using catalysts.

Function of Catalysts
- Catalysts lower the activation energy required for reactions.
- Enzymes are biological catalysts that increase the rate of reactions without being consumed.

Structure and Function
- ATP is the primary energy currency in cells, composed of ribose, adenine, and a chain of three phosphates.
- Energy is released upon hydrolysis of ATP to ADP and Pi (inorganic phosphate).
- ATP hydrolysis drives endergonic reactions in the cell but is not suitable for long-term energy storage; fats and carbohydrates are preferred.

Basic Characteristics of Enzymes
- Enzymes bind substrates at their active sites to form enzyme-substrate complexes, facilitating reactions via induced fit.
- Enzymes can be influenced by environmental factors such as temperature and pH, and their activity may be altered by inhibitors or activators.

Types of Inhibition
- Competitive Inhibitors: Compete with substrate for the active site.
- Noncompetitive Inhibitors: Bind to the enzyme elsewhere, affecting activity without competing with the substrate.
- Allosteric Regulation: Enzymes can exist in active or inactive forms, with allosteric sites affecting their function.

Mechanism of Feedback Inhibition
- End products of a biochemical pathway may inhibit earlier steps, preventing waste of resources and energy.
- This regulatory mechanism ensures metabolic efficiency and balance in the cell.