🧬 Chapter 3: Biological Molecules

📚 Section 1: Vocabulary Matching ⏱ ~5 min

Match each macromolecule term with its correct definition.

🔬 Section 2: Key Figures ⏱ ~6 min

Study these key OpenStax figures covering all four macromolecule types. Click each to reveal its description.

Figure 3.2 Dehydration synthesis: Two glucose molecules link to form maltose (a disaccharide). A water molecule is removed in the process. This is how all polymers are built — monomers join as water leaves.

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Figure 3.5 Glucose, galactose, and fructose are all hexoses (C₆H₁₂O₆) but are structural isomers — same formula, different arrangement of atoms. This demonstrates that structure determines function in biology.

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Figure 3.16 Saturated fatty acids have only single bonds between carbons (straight, solid at room temp). Unsaturated fatty acids have one or more double bonds causing kinks (liquid at room temp, like oils).

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Figure 3.20 The phospholipid bilayer is the major component of all cell membranes. Hydrophilic phosphate heads face the water on both sides, while hydrophobic fatty acid tails face inward, away from water. This creates a selectively permeable barrier.

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Figure 3.30 Four levels of protein structure: (1) Primary — amino acid sequence, (2) Secondary — α-helices and β-pleated sheets from H-bonding, (3) Tertiary — 3D folding from R-group interactions, (4) Quaternary — multiple polypeptide subunits joined together.

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Figure 3.32 DNA is an antiparallel double helix. The sugar-phosphate backbone runs in opposite directions (5'→3' and 3'→5'). Complementary base pairs (A-T, G-C) are connected by hydrogen bonds in the center. This structure allows DNA replication and information storage.

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🔄 Section 3: Sort the Macromolecules ⏱ ~5 min

Click each item below to assign it to the correct macromolecule category. Select a chip, then click the correct category.

Click an item, then click a category above:

✅ Section 4: Concept Check ⏱ ~8 min

Test your understanding of the four macromolecules.

1. What type of reaction links monomers together to form a polymer?

Hydrolysis

Dehydration synthesis (condensation)

Oxidation

Fermentation

💡 Need a hint?

Look at the diagram — what small molecule is released when two glucose molecules bond?

Why this is correct: Dehydration synthesis (also called condensation) removes a water molecule to form a covalent bond between two monomers. This is how glucose → maltose, amino acids → proteins, and nucleotides → DNA are all built. Hydrolysis is the reverse — it breaks bonds by adding water.

2. Why do unsaturated fats tend to be liquid at room temperature?

They have more carbon atoms than saturated fats

They contain nitrogen atoms

They dissolve in water more easily

Double bonds create kinks that prevent tight packing

💡 Need a hint?

Compare the shapes in the diagram — straight chains vs. kinked chains. Which can pack together more tightly?

Why this is correct: The cis double bonds in unsaturated fatty acids create kinks in the hydrocarbon chains. These kinks prevent the molecules from packing tightly together, so they remain liquid (oils) at room temperature. Saturated fats with straight chains pack tightly, forming solids (like butter).

3. Which level of protein structure is determined by the specific amino acid sequence?

Quaternary structure

Tertiary structure

Primary structure

Secondary structure

💡 Need a hint?

Think about what comes "first" in protein folding — before any 3D shape forms...

Why this is correct: Primary structure is the linear sequence of amino acids in a polypeptide chain, determined by the gene that codes for it. This sequence dictates all higher levels of structure: secondary (α-helices, β-sheets), tertiary (3D folding), and quaternary (multi-subunit assembly). A single amino acid change can alter the entire protein (like in sickle cell disease).

5. What is the function of the phospholipid bilayer?

To store genetic information

To form a selectively permeable barrier around cells

To provide energy for cellular processes

To catalyze chemical reactions

💡 Need a hint?

The hydrophilic heads face water while hydrophobic tails hide inside. What kind of barrier does this create?

Why this is correct: Phospholipid bilayers form cell membranes — selectively permeable barriers that control what enters and exits the cell. The hydrophilic heads face the aqueous environment while hydrophobic tails form the interior, blocking polar/charged molecules while allowing small nonpolar molecules through.

💡 Section 5: Apply Your Knowledge ⏱ ~5 min

Answer these short response questions (minimum 30 characters each).

Question 1

Sickle cell disease is caused by a single amino acid change in hemoglobin (glutamic acid → valine). Using your knowledge of protein structure, explain why this small change can have such a dramatic effect.

Question 2

Why can humans digest starch (from bread and potatoes) but not cellulose (fiber from vegetables), even though both are made of glucose?

🎯 Section 6: Final Reflection ⏱ ~2 min

Write a brief reflection: Why is understanding biological macromolecules important for understanding all of biology? How do the four types work together in a living cell? (Minimum 100 characters)