Each year in my school district, we were required to attend a system-wide inservice meeting for all the science teachers in our district. In attendance were science teachers of grades 7 through 12. These events are fun and interesting, mostly because I have been teaching for 28 years, and it is nice to see science teachers from other schools that I have known for years but rarely get to see. After joining up with a group of old acquaintances, the inevitable question came up: "What have you been doing in your biology classes?"
I responded with, "I have just finished teaching a unit on enzymes to our Biology 1 students." One of the other teachers immediately responded with, "I don't really teach that in my class."
What???? How do you NOT teach about enzymes in a biology class???? As soon as I returned home that day, I promptly sent her all of my teaching materials on enzymes.
I have always considered enzymes to be an essential part of high school biology. Students need to understand how enzymes work before they can fully appreciate many of the processes that keep living organisms alive. Whether you are teaching biochemistry, photosynthesis, cellular respiration, or digestion, enzymes are involved. I want my students to understand not only what enzymes are but also why they are so important.
Why Is Teaching Enzymes Important in Biology?
Enzymes are the stuff of life! No cell could survive without the action of enzymes. Hundreds of different chemical reactions are constantly occurring inside living cells, and many of these reactions would proceed far too slowly under normal cellular conditions without the help of enzymes.
Enzymes are biological catalysts. They increase the rates of chemical reactions by lowering the activation energy needed for those reactions to occur. This allows essential cellular processes to take place faster and at lower temperatures.
Think about all the processes students learn during a biology course. Cells break down nutrients, build proteins, copy DNA, release energy from food, and carry out countless other chemical reactions. Enzymes play important roles in these activities, making them a concept students will encounter repeatedly throughout the year.
When Should You Teach Enzymes in High School Biology?
I begin teaching enzymes during my biochemistry unit. When students are learning about carbohydrates, lipids, proteins, and nucleic acids, it is a natural time to introduce the structure and function of enzymes. Most enzymes are proteins, so students can connect what they have learned about protein structure to the role of enzymes in cells.
But I certainly don't stop teaching enzymes when the biochemistry unit ends! I revisit enzyme function when teaching photosynthesis, cellular respiration, DNA replication, transcription, and digestion. Enzymes are involved in so many biological processes that students have repeated opportunities to apply what they have learned.
This is one reason I think enzymes deserve more than a passing mention in the curriculum. A strong understanding of enzyme function early in the year makes many later biology topics much easier for students to understand.
Essential Enzyme Concepts Students Need to Understand
There are several important ideas I want every student to understand before we move on from our initial enzyme lessons. These concepts provide the foundation for laboratory investigations, graphing activities, and later discussions of cellular processes.
1. Enzymes Are Biological Catalysts
Enzymes speed up chemical reactions by lowering their activation energy. Activation energy is the energy required to begin a chemical reaction. By providing an alternative reaction pathway with a lower activation-energy barrier, an enzyme allows the reaction to proceed more rapidly.
Enzymes do not provide energy to a reaction, change the overall energy difference between reactants and products, or change the position of chemical equilibrium. They simply help the reaction reach equilibrium more quickly.
2. Most Enzymes Are Proteins
Most enzymes are proteins with specific three-dimensional structures that allow them to perform their functions. Protein folding is important because an enzyme's shape helps determine how it interacts with the molecules involved in a chemical reaction.
There are also catalytic RNA molecules called ribozymes, so it is more scientifically accurate to say that most enzymes are proteins rather than all enzymes are proteins.
3. Enzymes Have Active Sites and Interact With Substrates
The substance an enzyme acts upon is called its substrate. The substrate interacts with a particular region of the enzyme called the active site. The active site's shape and chemical properties help determine which substrates the enzyme can bind and which reactions it can catalyze.
I like to introduce this idea with a simple enzyme-substrate diagram. Students can follow the substrate as it binds to the enzyme, forms an enzyme-substrate complex, and is converted into products.
Enzymes are often described using the lock-and-key model, but I also explain that enzymes are flexible molecules. In the induced-fit model, binding of the substrate can cause changes in the shape of the enzyme's active site. This helps students understand why enzyme action is more complex than two rigid puzzle pieces fitting together.
Enzymes are usually selective for particular substrates or groups of closely related substrates. It is important for students to understand this specificity without assuming that every enzyme acts on only one molecule under all circumstances.
4. Enzymes Are Not Used Up During Reactions
Another important concept is that enzymes are not consumed during the reactions they catalyze. After a reaction is completed and the products are released, the enzyme can participate in another reaction.
An enzyme may catalyze the same reaction repeatedly, provided it remains functional and the necessary substrates and conditions are available. Enzymes may eventually become damaged or broken down, but they are not used up as ordinary reactants in the reactions they catalyze.
5. Temperature and pH Affect Enzyme Activity
Students also need to understand that enzymes work best under particular environmental conditions. Temperature and pH can influence enzyme activity, and different enzymes have different optimal conditions.
As temperature increases, the rate of an enzyme-catalyzed reaction often increases until an optimal range is reached. At excessively high temperatures, an enzyme may lose the structure necessary for proper functioning. This change, called denaturation, can reduce or eliminate enzyme activity. At lower temperatures, reaction rates generally decrease, but the enzyme is not necessarily denatured.
Changes in pH can also affect the chemical properties and structure of an enzyme, including its active site. Extreme pH conditions may cause denaturation, while less extreme changes may alter enzyme activity without permanently damaging the enzyme.
This provides a useful connection to the concept of homeostasis. Living cells must maintain conditions that allow enzymes and other cellular components to function properly. If you want to extend this discussion, take a look at my article, How Do Living Cells Deal With Changes?, for a classroom investigation involving cells, pH, and buffers.
Introducing Enzymes With a PowerPoint Lesson and Guided Notes
When I first introduce enzymes, I want students to see how chemical reactions and catalysts relate to the processes occurring inside living cells. I begin with the basics of chemical reactions and energy changes, then explain how enzymes function, why substrates interact with active sites, and what happens when environmental conditions change.
For these lessons, I use my Enzymes PowerPoint and Notes. It includes 36 instructional slides, complete teacher notes, and guided student notes. Students complete their notes as the lesson progresses, giving them an organized reference for later practice and review.
I find that students benefit from having diagrams and examples available as they learn the vocabulary. Once students understand the basic concepts, I like to give them opportunities to apply that knowledge rather than simply memorizing definitions.
Using Graphing Activities to Teach Enzyme Function
One of my favorite ways to reinforce enzyme concepts is through graphing and data analysis. Students need to understand more than the definition of an enzyme. They should be able to interpret what happens to the rate of an enzyme-catalyzed reaction when temperature, pH, or reaction time changes.
Graphing activities help students make those connections while strengthening another important science skill. When students construct graphs from data tables and answer questions about the results, they have to apply their understanding of enzyme function to a new situation.
My Enzymes Graphing Activities resource includes three graphing exercises. Students analyze an enzyme-catalyzed reaction over time, investigate the effects of temperature on enzyme activity, and examine how pH influences enzyme functioning. Each exercise includes follow-up questions that encourage students to interpret the data and explain what their graphs show.
This is an activity I like because it reinforces enzyme concepts and provides valuable practice with scientific graphing. It also works well as independent practice, homework, or review when students need additional experience interpreting biological data.
Take a closer look at the Enzymes Graphing Activities and Critical Thinking Questions.
Reviewing and Reinforcing Enzyme Concepts
After students have learned the basic vocabulary and practiced interpreting enzyme data, I like to provide additional opportunities for review. Not every student learns a concept the first time it is presented, and enzyme vocabulary can be particularly challenging. Terms such as activation energy, substrate, active site, enzyme-substrate complex, and denaturation need repeated reinforcement.
One way I review these ideas is with Enzymes Task Cards. Students answer questions about enzyme structure, function, and the factors that affect enzyme activity. The cards can be used for individual review, partner work, small groups, or a classroom review activity.
For additional independent practice, I also use Enzymes Homework Worksheets. These give students another opportunity to work with the content after the lesson. For a different style of review, my Enzymes Color by Number activity offers a way to reinforce important enzyme concepts while providing a change of pace from traditional worksheets.
I like having several types of review activities available because they make it easier to adjust instruction to the needs of a particular class. Some groups need more independent practice, while others benefit from discussion, diagrams, and collaborative review.
Hands-On Enzyme Labs and Investigations
Of course, I don't want students to learn about enzymes only through notes, diagrams, and worksheets. Whenever possible, I like to include laboratory investigations that allow students to observe evidence of enzyme activity and analyze experimental results.
One of my favorite investigations is The Effect of the Enzyme Amylase on Starch. In this lab, students investigate what happens when the enzyme amylase interacts with starch. They use chemical tests to collect evidence about the substrate, the products of the reaction, and the enzyme itself.
Students use iodine to test for starch, Benedict's solution to test for reducing sugars, and Biuret reagent to test for proteins. These observations help students develop conclusions about enzyme activity, the breakdown of starch, and substrate specificity.
You can read more about the investigation in my amylase on starch lab blog post, or find the complete Effect of Amylase on Starch laboratory activity in my TpT store.
Planning a Complete Enzymes Unit for High School Biology
When I plan my enzyme instruction, I want students to move from understanding basic ideas to using those ideas in meaningful ways. I begin by introducing chemical reactions, activation energy, and the structure and function of enzymes. From there, students practice interpreting diagrams, analyze data, and investigate how enzymes work under different conditions.
I also make sure students understand that enzymes are not isolated vocabulary terms. Enzyme function connects to protein structure, cellular respiration, digestion, homeostasis, and many other topics they will encounter throughout biology.
For teachers who would rather have a collection of coordinated resources than assemble individual materials, I offer an Enzymes and Chemical Reactions Unit Bundle. It brings together instructional resources and student activities to support teaching this important topic.
Whether you are preparing an entire enzyme unit or looking for one activity to reinforce a difficult concept, the important thing is to give students enough opportunities to understand how enzymes function and why they matter.
Don't Leave Enzymes Out of Your Biology Curriculum!
I still think about that conversation at our science teachers' meeting. Enzymes are so important to the functioning of living cells that I cannot imagine teaching biology without giving them the attention they deserve!
Students will encounter enzymes again and again as they study the processes of life. By teaching the basic concepts carefully and reinforcing them through diagrams, graphing, review activities, and laboratory investigations, we can help students develop a foundation that will serve them throughout the course.
Enzymes really are the stuff of life. Make sure your students understand why!
