Enzymes are one of the most important biological concepts in the IB Biology syllabus. They appear throughout topics on metabolism, digestion, DNA replication, cellular respiration, and photosynthesis. Because enzymes control nearly every chemical reaction in living organisms, understanding how they work is essential for exam success. This is why strong students master enzyme fundamentals early, following strategies such as those in How to Pass IB Biology SL Exams (https://www.revisiondojo.com/blog/how-to-pass-ib-biology-sl-exams-proven-study-strategy) .
What Exactly Are Enzymes?
Enzymes are biological catalysts—proteins that speed up chemical reactions without being used up in the process. They allow reactions that would normally occur too slowly to happen fast enough to sustain life. Without enzymes, metabolism would break down instantly.
Enzymes are made of long chains of amino acids folded into precise three-dimensional shapes. These structures form the active site, where the substrate (the molecule the enzyme acts on) binds. Understanding protein structure and bonding helps explain enzyme function, and this level of biochemical detail becomes especially important in HL, as described in IB Biology HL vs SL: 7 Key Differences (https://www.revisiondojo.com/blog/ib-biology-hl-vs-sl-difficulty-7-key-differences-every-ib-student-must-know) .
How Enzymes Work: The Lock-and-Key and Induced Fit Models
Enzymes work by lowering the activation energy required for a reaction. They do this by binding substrates at their active site and helping convert them into products.
Two models explain this:
1. Lock-and-Key Model
- The active site has a fixed shape.
- Only specific substrates with the correct shape can bind.
- Often used to explain enzyme specificity.
