Ch+6+FP-module 5

Chapter 6: Energy and Enzymes

Energy Transformation

• Cells act as small chemical factories; many reactions require energy.

• Energy: the capacity to perform work; moves matter against forces (e.g., friction, gravity).

  • Kinetic Energy: energy of motion.

    • Examples: moving organisms or organelles, heat, light.

  • Potential Energy: stored energy due to position or structure.

    • Examples: compressed spring, a ball at the top of a hill.

  • Chemical Energy: form of potential energy stored in bonds.

• Energy can be converted from one form to another.

Laws of Thermodynamics

• Thermodynamics: study of energy transformation.

• First Law: Energy is neither created nor destroyed, only converted.

• Second Law: In every energy conversion, some energy is lost; it becomes random molecular movement (heat), increasing disorder (entropy).

• Cells require a constant input of ordered energy to maintain organization.

Chemical Notation

• Reactants: starting materials of a chemical reaction, listed on the left of the arrow.

• Products: new materials produced in a reaction, found on the right of the arrow.

  • Example: A + B → C + D.

Energy and Reactions

• Exergonic Reactions: high-energy reactants yield lower-energy products; they release energy.

  • Example: Wood burning releases energy instantly.

  • Cellular respiration is exergonic; energy is released gradually to be stored as ATP instead of lost as heat.

• Endergonic Reactions: low-energy reactants convert to high-energy products; they require an input of energy.

  • Example: Photosynthesis involves energy from sunlight, converting CO2 and water into high-energy sugars.

  • ATP is typically the energy source for macromolecule construction in cells.

Cell Metabolism

• Refers to the total of all cell reactions: anabolic (building) and catabolic (breaking down).

• Most reactions occur in linked steps called metabolic pathways, where products of one step become the reactants of the next.

• Cells use energy coupling through ATP to pair energy-producing exergonic reactions with energy-requiring activities.

  • Analogy: ATP is like money; you do work to earn it and spend it on necessities.

ATP—Adenosine Triphosphate

• A modified nucleotide with three negatively-charged phosphate groups.

• High potential energy due to unstable bonds; breaking down ATP into ADP + phosphate releases energy.

Cellular Work

• ATP is generated during respiration and used for:

  • Endergonic chemical reactions.

  • Movement (proteins, muscle contraction, vesicles, chromosomes).

  • Active and bulk transport.

ATP Cycle

• Respiration generates ATP through exergonic breakdown of glucose/carbohydrates.

• Cells break down ATP to fuel endergonic reactions; ADP + phosphate is recycled during respiration.

• Each ATP molecule can be recycled over 1000 times daily—approximately equal to one’s weight in ATP for humans.

Enzymes and Energy

• Reactions have activation energy barriers (Ea); existing bonds must weaken before breaking.

• Catalysts lower Ea, thus speeding reactions.

  • Enzymes: biological, protein-based catalysts that are not consumed in reactions. One enzyme can catalyze repeated reactions.

  • Catalysts are represented above arrows in equations: Enzyme A + B → C + D.

Enzyme Specificity

• Enzymes catalyze specific reactions based on their shape.

• A reactant in an enzyme-driven reaction is called a substrate.

• Only properly fitting substrates bind to the enzyme's active site.

  • Induced Fit: active site changes shape to hold substrates firmly, positioning them for reaction.

  • Products are released, and the enzyme is available for new reactions.

Names of Enzymes

• Enzymes named after substrates/processes with suffix +ase indicating they are enzymes:

  • Proteases: break down proteins.

  • Lipidases: break down lipids.

  • Amylases: break down starch.

  • Kinases: add ATP energy to proteins.

Factors Affecting Enzymes

• Enzymes require the proper shape to function; environmental factors can alter shape.

  • Significant for maintaining homeostasis; improper conditions can lead to denaturation.

• Temperature affects reaction rates:

  • Cold temperatures: enzymes and substrates interact less frequently, slowing reactions.

  • Increased temperatures: reactions speed up until a threshold (too hot leads to denaturation).

• pH levels affect enzyme activity; enzymes have an optimum pH for functioning.

Factors Affecting Enzymes (cont.)

• Enzyme or substrate concentration impacts reaction speed.

  • Low concentration: low likelihood of interaction, slowing reactions.

  • Speed increases with concentration until a maximum is reached.

• Some enzymes require modifications or cofactors (inorganic or organic) to activate:

  • Nutrient-based minerals (iron, zinc, copper) often act as cofactors.

  • Vitamins can be coenzymes or precursors for enzyme activation.

Inhibitors Prevent Enzyme Function

• Competitive Inhibitors: block active sites.

• Non-competitive Inhibitors: bind elsewhere, altering active site shape.

• Inhibitors can be toxins or serve species by defending against predators.

• Not always detrimental; cells can use inhibitors to regulate enzyme activity.

Feedback Inhibition

• Many reactions occur in metabolic pathways with several steps catalyzed by different enzymes.

• Feedback Inhibition: end products serve as inhibitors to earlier enzymes.

  • When final product levels are high, it stops the pathway, preventing energy waste.

  • Pathway resumes once the product is consumed.

Redox Reactions

• Redox reactions involve electron transfer between reactants; both processes must occur together.

  • Oxidation: loss of electrons.

  • Reduction: gain of electrons.

• Mnemonics: LEO goes GER (Lose Electrons Oxidized, Gain Electrons Reduced) or OIL RIG (Oxidation Is Loss, Reduction Is Gain).

• Photosynthesis and respiration are redox reactions:

  • In cellular reactions, follow hydrogens:

    • Loss of hydrogen: oxidation (e.g., glucose in respiration).

    • Gain of hydrogen: reduction (e.g., oxygen in respiration).

Photosynthesis and Respiration Chemical Equations

• Photosynthesis: Sun energy + 6CO2 + 6H2O → C6H12O6 + 6O2.

• Respiration: C6H12O6 + 6O2 → 6CO2 + 6H2O + ATP.

• Coefficient numbers indicate quantity needed for reactions; equations are mirror images minus energy content.

• Both plant and animal cells perform respiration; remember the 2nd Law: some energy is lost as heat during both processes.