Organic Molecules, Macromolecules, Membrane Transport, and Enzyme Function: Study Guide

Organic Molecules and Macromolecules

Definition and Characteristics

Organic molecules are compounds that contain both carbon and hydrogen. Macromolecules are large, complex molecules essential for life, including carbohydrates, proteins, lipids, and nucleic acids.

• Organic Molecules: Contain carbon and hydrogen atoms.

• Macromolecules: Include carbohydrates, proteins, lipids, and nucleic acids.

• Polymers: Carbohydrates, proteins, and nucleic acids form polymers from monomers; lipids do not form polymers.

Macromolecule Construction and Breakdown

Macromolecules are built and broken down through specific chemical reactions, often facilitated by enzymes.

• Dehydration Synthesis: Removal of a water molecule to link two monomers, forming a covalent bond. Requires enzymes and energy.

• Hydrolysis: Addition of a water molecule to break apart two monomers, breaking covalent bonds. Requires enzymes and releases energy.

Types of Macromolecules

• Carbohydrates: Composed of carbon, hydrogen, and oxygen. Used for energy storage and structural support. Monomers include glucose, fructose, and galactose. Examples: starch, glycogen, cellulose.

• Proteins: Composed of carbon, hydrogen, oxygen, and nitrogen. Functions include cellular transport, structural support, enzymatic activity, and communication. Monomers are amino acids, which form polypeptide chains.

• Nucleic Acids: Composed of carbon, hydrogen, oxygen, nitrogen, and phosphorus. Used for information storage. Monomers are nucleotides. Polymers are DNA and RNA.

• Lipids: Composed of carbon, hydrogen, oxygen, and phosphorus. Used for insulation, energy storage, and signaling. Do not form polymers. Common lipids: fatty acids, triglycerides, phospholipids.

Laboratory Tests for Macromolecules

Testing for Reducing Sugars (Benedict's Reagent)

Reducing sugars can donate electrons, resulting in a color change with Benedict's reagent.

• Positive Result: Red-orange (large amount), yellow or green (small amount).

• Negative Result: Blue to purple (color of reagent).

• Examples: Glucose and fructose are reducing sugars.

Testing for Starch (Lugol's/Iodine Reagent)

• Starch: Large complex carbohydrate.

• Positive Result: Color change to blue/brown/black.

Testing for Protein (Biuret's Reagent)

• Positive Result: Bright purple color.

Testing for Lipids (Sudan IV Reagent)

• Positive Result: Separation and orange color.

Membrane Transport

Types of Solutions

Cells interact with their environment based on solute concentration across membranes.

• Hypertonic: Higher solute concentration outside the cell.

• Hypotonic: Lower solute concentration outside the cell.

• Isotonic: Equal solute concentration inside and outside the cell.

Facilitated Diffusion

Facilitated diffusion is a passive process where molecules move down their concentration gradient with the help of membrane proteins.

• Passive: No energy required.

• Large Molecules: Require facilitation by specific plasma membrane proteins.

Active Transport

Active transport moves molecules against their concentration gradient, requiring energy (ATP) and membrane proteins.

• Requires ATP: Energy is needed to move molecules from low to high concentration.

• Example: Sodium-potassium pump.

Laboratory Activities

• Dialysis Tubing: Used to simulate a cell and test diffusion of various solutes.

• Surface Area & Volume: As cell volume increases, surface area increases less rapidly. Cells must remain small for efficient diffusion.

Enzyme Function

Enzymes and Catalysis

Enzymes are protein molecules that act as biological catalysts, speeding up chemical reactions without being consumed.

• Active Site: Region where substrate binds ('lock and key' fit).

• Substrate: Specific molecule acted upon by the enzyme.

• Example: Catalase converts hydrogen peroxide ($H_2O_2$) into water ($H_2O$) and oxygen ($O_2$).

Activation Energy

Activation energy ($E_A$) is the energy required to start a reaction. Enzymes lower activation energy, enabling reactions to occur faster.

• Equation:

$\Delta G = G_{products} - G_{reactants}$

Enzymes do not change $\Delta G$, but lower $E_A$.

Enzyme Inhibitors

• Inhibitors: Molecules that bind to enzymes and alter their shape, preventing substrate conversion.

Factors Affecting Enzyme Activity

• Temperature

• pH

• Salt Concentration

• Presence of Inhibitors

Laboratory Activity: Effect of Temperature on Catalase

• Test catalase activity at different temperatures (hot, room, ice) by measuring oxygen released from breakdown of hydrogen peroxide.

Summary Table: Macromolecules

Macromolecule	Elements	Monomer	Polymer	Function	Example
Carbohydrates	C, H, O	Monosaccharide	Polysaccharide	Energy storage, structure	Starch, glycogen, cellulose
Proteins	C, H, O, N	Amino acid	Polypeptide	Transport, structure, enzymes	Hemoglobin, catalase
Nucleic Acids	C, H, O, N, P	Nucleotide	DNA, RNA	Information storage	DNA, RNA
Lipids	C, H, O, P	Fatty acid (not a true monomer)	Do not form polymers	Insulation, energy storage, signaling	Triglycerides, phospholipids

Additional info:

• Living organisms are composed primarily of oxygen, hydrogen, carbon, and nitrogen.

• Carbohydrates, proteins, and nucleic acids can exist as single monomers or as polymers.