Unit 8: Energy, Enzymes, & Organisms – Study Notes

Energy Forms & Transformations

Types of Energy

Energy exists in various forms within biological systems, each with distinct properties and roles in cellular processes.

• Mechanical Energy: Energy associated with motion or position of an object (e.g., muscle contraction).

• Chemical Energy: Energy stored in chemical bonds of molecules (e.g., glucose, ATP).

• Thermal Energy: Energy related to the random movement of atoms and molecules; often released as heat.

• Light Energy: Energy in the form of electromagnetic radiation, essential for processes like photosynthesis.

Kinetic Energy is the energy of motion, while Potential Energy is stored energy due to position or structure. For example, a stretched spring has potential energy, while a moving car has kinetic energy.

Thermodynamics in Biology

Thermodynamics governs energy transformations in biological systems.

• First Law of Thermodynamics: Energy cannot be created or destroyed, only transformed from one form to another.

• Second Law of Thermodynamics: Every energy transfer increases the entropy (disorder) of the universe; some energy is always lost as heat.

• Entropy (S): A measure of disorder or randomness. Systems tend to move toward higher entropy.

• Chemical Energy vs. Free Energy: Chemical energy is stored in bonds; free energy (Gibbs free energy) is the portion available to do work. Thermal energy is often released as a byproduct, increasing entropy.

Example: In cellular respiration, glucose is broken down, releasing energy for cellular work and increasing entropy by producing heat and waste products.

Reactions, Enzymes, & ATP

Endergonic and Exergonic Reactions

Chemical reactions in cells can either absorb or release energy.

• Endergonic Reactions: Require an input of energy; products have more free energy than reactants (e.g., photosynthesis).

• Exergonic Reactions: Release energy; products have less free energy than reactants (e.g., cellular respiration).

• Synthesis (Dehydration Synthesis): Building larger molecules from smaller ones by removing water.

• Decomposition (Hydrolysis): Breaking down molecules by adding water.

Graphical Models: Endergonic reactions show an upward curve (energy input), while exergonic reactions show a downward curve (energy release).

Enzymes and Activation Energy

Enzymes are biological catalysts that speed up chemical reactions by lowering the activation energy required.

• Activation Energy (Ea): The minimum energy needed to start a reaction.

• Enzyme-Substrate Interaction: Enzymes have an active site where substrates bind, forming an enzyme-substrate complex. The enzyme facilitates the reaction and releases the product.

• Induced Fit: The enzyme changes shape slightly to fit the substrate more closely.

• Effect of Environment: Temperature, pH, and other factors can affect enzyme activity. Extreme conditions may denature (unfold) the enzyme, reducing its function.

Example: The enzyme lactase breaks down lactose into glucose and galactose.

ATP: The Energy Shuttle

ATP (adenosine triphosphate) is the primary energy carrier in cells, transferring energy for cellular work.

• ATP Structure: Composed of adenine, ribose, and three phosphate groups.

• ATP Hydrolysis: Breaking the terminal phosphate bond releases energy ($\mathrm{ATP} + \mathrm{H}_2\mathrm{O} \rightarrow \mathrm{ADP} + \mathrm{P}_i + \text{energy}$).

• Cellular Work Driven by ATP:

  • Mechanical Work: Muscle contraction, movement of cilia/flagella.

  • Transport Work: Pumping substances across membranes.

  • Chemical Work: Driving endergonic reactions (e.g., synthesis of macromolecules).

Example: ATP powers the sodium-potassium pump in nerve cells.

Digestion

Chemical Digestion and Enzymes

Chemical digestion involves breaking down biomolecules into monomers using hydrolysis, facilitated by specific enzymes.

• Hydrolysis: Addition of water to break bonds in polymers (e.g., proteins to amino acids).

• Dehydration Synthesis: Removal of water to form bonds between monomers (e.g., forming proteins from amino acids).

• Enzymes in Digestion:

  • Salivary Amylase: Breaks down starch into sugars.

  • Protease: Breaks down proteins into amino acids.

  • Lipase: Breaks down lipids into fatty acids and glycerol.

  • Lactase: Breaks down lactose into glucose and galactose.

Example: In lactose-intolerant individuals, the enzyme lactase is deficient, leading to difficulty digesting lactose.

Biomolecule Monomers and Polymers

Understanding the building blocks of biomolecules is essential for grasping digestion and metabolism.

• Carbohydrates: Monomers are monosaccharides (e.g., glucose); polymers are polysaccharides (e.g., starch).

• Proteins: Monomers are amino acids; polymers are polypeptides/proteins.

• Lipids: Monomers are fatty acids and glycerol; polymers are triglycerides.

• Nucleic Acids: Monomers are nucleotides; polymers are DNA/RNA.

Key Vocabulary and Root Words

Important Terms

• Activation Energy

• Active Site

• ADP

• ATP

• Cellular Respiration

• Chemical Energy

• Denature

• Energy

• Entropy

• Enzyme

• Endothermic (Endergonic)

• Exothermic (Exergonic)

• First Law of Thermodynamics

• Heat

• Induced Fit

• Kinetic Energy

• Metabolic Pathway

• Metabolism

• Potential Energy

• Second Law of Thermodynamics

• Substrate

• Thermodynamics

Root Words

• endo- = inner, within

• -ase = enzyme

• exo- = outer

• kinet- = movement

• therm- = heat

Chapter 21 Vocabulary

• Lactose

• Lactase

• Salivary Amylase

• Protease

• Lipase

• Synthesis

Unit 6 Review

• Hydrolysis

• Dehydration Synthesis

• Biomolecule Monomers and Polymers