🧬 Strand A: Biochemistry

Course: SBI4U — Biology, Grade 12, University Preparation
Curriculum Expectation: Demonstrate understanding of the structures and functions of biological molecules

1. Elements of Life

Living organisms are composed primarily of six elements: carbon (C), hydrogen (H), oxygen (O), nitrogen (N), phosphorus (P), and sulfur (S) — collectively known as CHONPS.

Key Concept: Carbon is the backbone of all organic molecules because it can form 4 covalent bonds, creating chains, branches, and rings — allowing enormous structural diversity.

2. The Four Macromolecules

Carbohydrates Monomer: Monosaccharide (glucose, fructose) Bond: Glycosidic Function: Energy, Structure Lipids Monomer: Fatty acids + Glycerol Bond: Ester Function: Energy, Membrane Proteins Monomer: Amino acid (20 types) Bond: Peptide Function: Enzymes, Structure Nucleic Acids Monomer: Nucleotide (sugar+base+phosphate) Bond: Phosphodiester Function: Genetic info Dehydration Synthesis vs Hydrolysis Dehydration: monomers → polymer + H₂O (builds) Hydrolysis: polymer + H₂O → monomers (breaks) These are reverse reactions catalyzed by enzymes

Comparison Table

MacromoleculeMonomerBond TypeElementsExamplesFunctions
CarbohydratesMonosaccharideGlycosidicC, H, OGlucose, starch, celluloseQuick energy, structural support
LipidsFatty acids + glycerolEsterC, H, OFats, oils, phospholipidsLong-term energy, cell membranes
ProteinsAmino acidPeptideC, H, O, N, SEnzymes, hemoglobin, collagenCatalysis, transport, structure
Nucleic AcidsNucleotidePhosphodiesterC, H, O, N, PDNA, RNA, ATPGenetic information, energy transfer

3. Enzymes

Enzymes are biological catalysts (proteins) that speed up chemical reactions by lowering the activation energy. They are specific to their substrate (lock-and-key model / induced fit model).
Enzyme Active Site → E-S Complex Substrate → Products + Enzyme (unchanged)

Factors Affecting Enzyme Activity

📝 Worksheet — Strand A: Biochemistry

1. [K/U — 4 marks] Complete the table:

MacromoleculeMonomerBondOne Function
Carbohydrate
Protein
Lipid
Nucleic Acid

2. [K/U — 2 marks] Explain the difference between dehydration synthesis and hydrolysis. Include the role of water in each.

3. [Thinking — 3 marks] A patient has a fever of 41°C. Explain, using your knowledge of enzyme structure and function, why prolonged high fever can be dangerous at the cellular level.

4. [Application — 3 marks] Lactose intolerance occurs when a person lacks the enzyme lactase. Using the lock-and-key model:

a) Explain why lactase only breaks down lactose and not other sugars.

b) Suggest why taking a lactase supplement before eating dairy products helps.

5. [Communication — 3 marks] Draw and label a graph showing enzyme activity vs. temperature. Mark the optimal temperature and the point of denaturation. Explain the shape of your graph in 2-3 sentences.

6. [Thinking — 4 marks] Explain the difference between competitive and non-competitive inhibition. For each:

a) Where does the inhibitor bind?

b) How does it affect enzyme activity?

c) Can the effect be reversed by adding more substrate? Explain.

7. [Application — 3 marks] Many household cleaners contain enzymes (e.g., proteases in laundry detergent). Why do these products often include instructions to use warm (not hot) water? Connect your answer to enzyme kinetics.

SBI4U — Biology, Grade 12 | Strand A: Biochemistry | Ontario Curriculum 2008