SBI4U Biochemistry Practice: Macromolecules and Enzyme Questions

To answer SBI4U biochemistry questions well, connect a structure or observation to a biological function. Naming a molecule is a start; explaining how its properties affect a process is the next step. For data questions, describe the measured pattern before proposing a mechanism.

This original practice set covers selected macromolecule and enzyme concepts. It is not a complete SBI4U assessment. Use your teacher’s terminology and the level of structural detail required in class.

Do I need to memorize everything in biochemistry?

Vocabulary and recognition matter, but memorized labels alone do not answer an explanation question. An SBI4U discussion highlights students’ concern about explaining processes in short answers. Treat that as a study question, not a prediction of the format of your own exam. Student discussion

A useful revision card has three parts: the term, a sketch or example, and a sentence explaining its function. Then test the connection with an unfamiliar example rather than only reciting the definition.

Ten original questions

• 1. What type of bond connects amino acids within a polypeptide chain?
• 2. A triglyceride is assembled from which two types of components, and in what numbers?
• 3. Why can phospholipids form a bilayer in water?
• 4. Explain one difference between dehydration synthesis and hydrolysis.
• 5. What does an enzyme change about the activation energy of a reaction? Does that mean it changes the reaction’s equilibrium position?
• 6. A high temperature reduces an enzyme’s activity after its shape changes. Explain the relationship between shape and function.
• 7. In a simplified enzyme model, reaction rate rises with substrate concentration and then approaches a plateau. Give a possible explanation for the plateau.
• 8. In a controlled illustrative experiment, rates at 10, 20, 30, 40 and 50°C are 2, 5, 9, 6 and 1 arbitrary units. Which tested temperature has the highest rate? Can you conclude the exact optimum is 30°C?
• 9. A student changes both pH and temperature between two enzyme trials. Why is it difficult to attribute a rate difference to pH alone?
• 10. Explain why “all lipids are polymers made of repeating monomers” is too broad a statement.

Explained answers

1. Link amino acids

A peptide bond connects amino acids in a polypeptide. Distinguish the covalent links in the chain from the interactions involved in folding the chain into a functional structure.

2. Identify the components of a triglyceride

A triglyceride contains one glycerol and three fatty-acid components, joined through ester linkages. The fatty-acid chains can differ. Naming the components is more precise than calling every lipid a chain of identical repeating units.

3. Explain the bilayer arrangement

Phospholipids have hydrophilic head regions and hydrophobic tails. In an aqueous setting, a bilayer places the heads toward water and the tails largely away from it. Link the arrangement to those properties rather than saying the molecules simply “want” to form a membrane.

4. Compare the role of water

In a typical dehydration-synthesis representation, building a bond releases water. Hydrolysis uses water in breaking a bond. State which process builds or breaks the relevant structure in the example rather than treating the words as interchangeable.

5. Separate rate from equilibrium

An enzyme lowers the activation-energy barrier by providing a catalytic pathway. It accelerates approach to equilibrium but does not change the equilibrium position for the reaction under the same conditions. A faster reaction is not automatically a reaction with a different final equilibrium composition.

6. Connect shape to binding and catalysis

A change in the protein’s structure can alter the active site and the interactions required for substrate binding or catalysis. Activity may therefore fall. Do not describe denaturation simply as every peptide bond being broken; changes in higher-level structure can disrupt function.

7. Interpret a plateau under stated assumptions

With a fixed amount of enzyme, increasing substrate can eventually leave active sites occupied much of the time. Adding more substrate then produces a smaller rate increase. This is a possible saturation explanation; confirm the model and controlled conditions before treating every plateau as proof of the same cause.

8. Distinguish a tested maximum from an exact optimum

The highest measured rate is 9 units at 30°C. The exact optimum could lie between tested temperatures. Additional measurements would be needed to locate it more closely. The values are invented for this practice question and do not describe a named enzyme.

9. Identify a confounded comparison

Both changed variables could affect the rate. To investigate pH, keep other relevant conditions comparable and vary pH systematically. The two-trial result alone does not isolate pH’s effect.

10. Avoid an overgeneralized category

Lipids are a diverse group. A triglyceride, for example, is not a long polymer of one repeating monomer in the way a polypeptide is a chain of amino-acid residues. Describe the actual molecule rather than forcing every biomolecule into the same structural pattern.

A simple structure for short answers

Begin with the claim, identify the relevant feature, and explain the connection. For a graph, first state the pattern with values or ranges, then explain a mechanism consistent with it. Keep observation and inference distinct.

If an answer says only “the enzyme denatured,” ask what changed and why that affects activity. If it says “the graph goes up,” identify the variables and the interval. These additions make the reasoning assessable.

Get support with biological explanations

Explore Grade 12 science tutoring or book a free one-hour assessment. For the earlier pathway, see our SBI3C and SBI3U comparison.

Curriculum reference: Ontario Grades 11–12 Science, SBI4U biochemistry. Questions and data are original practice material.