Chapter 5: The Dynamic Cell

Energy

• Capacity to do work.
• Biosphere energy source: the sun.

Types of Energy

• Potential: Stored energy.
• Kinetic: Energy of motion.
• Conversion between forms results in heat loss.

Thermodynamics Laws

• First law: Energy cannot be created or destroyed, only transformed.
• Second law: Energy transformation increases entropy (disorder), losing usable energy as heat.

Entropy

• Increase in disorganization/randomness.
• Maintaining order requires energy input.
• Universe is a closed system, energy transformations increase total entropy.
• Sun's energy allows plants to create glucose, some energy is lost as heat.

ATP: Energy Currency

• Adenosine triphosphate (ATP) is the energy currency of cells.
• Used for nearly all cellular activities.
• 1 nucleotide + 3 phosphate groups= unstable.
• Loses a phosphate group, becoming ADP (adenosine diphosphate).
• ATP releases energy, facilitating enzymatic reactions.
• Coupled reactions link energy-releasing with energy-requiring reactions, often via ATP breakdown.

Coupled Reaction Example

• Muscular contraction: ATP breakdown energizes myosin to pull actin, causing contraction.

Energy Flow

• Photosynthesis uses solar energy to convert water and CO2 into carbohydrates.
• Cellular respiration breaks down carbohydrates, producing ATP.
• Energy transformations result in loss of useful energy.

Metabolic Pathways and Enzymes

• Metabolic pathway: Series of linked reactions where product of one reaction is the reactant for the next.
• Enzymes: Organic catalysts (typically proteins) that speed up reactions.

Enzymes Action

• Act on substrates to facilitate breakdown or synthesis.
• Energy of activation (Ea): Energy needed for molecules to react.
• Enzymes lower Ea, accelerating reactions.

Enzyme's Active Site

• Accommodates substrate (lock and key model).
• Induced fit: Enzyme changes shape to fit substrate.
• Returns to original shape after releasing products; enzymes are not consumed.

Enzyme Inhibition

• Active enzyme is prevented from combining with its substrate.
• Feedback inhibition: Product competes with substrate for active site; end-product inhibits early enzyme, shutting down pathway.