Unit 6_Enzyme Basics: Structure and Function
Fundamental Biochemistry: Enzyme Structure and Function
Definition of an Enzyme
Enzymes are specialized PROTEINS that function to accelerate chemical reactions while requiring LESS energy to do so.
Rate and Activation Energy: Enzymes increase the RATE () of a chemical reaction while simultaneously decreasing the ACTIVATION ENERGY required to initiate that reaction.
Substrate Specificity: Enzymes are substrate-specific, meaning they possess a unique configuration that allows them to bind only to certain specific substrates.
Reusability: Enzymes are REUSABLE and are not consumed or permanently altered during the reaction process.
Ubiquity: Enzymes are present in ALL living things.
Necessity: Without the presence of an enzyme, a chemical reaction will still OCCUR; however, it will proceed at a significantly slower rate.
Enzymatic Nomenclature and Examples
Most enzyme names typically end with the suffix –ASE.
Lactase: An enzyme responsible for breaking down lactose within the digestive system.
Salivary Amylase: An enzyme present in saliva that initiates the breakdown of food in the mouth, facilitating a faster rate of digestion once the food reaches the stomach.
Sucrase: Specifically breaks down sucrose.
Proteases: Enzymes that breakdown proteins.
Key Components and Vocabulary
Substrate: The specific substance upon which an enzyme acts to produce a chemical reaction.
Active Site: The specific part of the enzyme that directly binds to the substrate; this is the physical location where the chemical reaction occurs.
Products: The converted substances that are produced by the enzyme-substrate complex after the reaction is complete.
Inhibitor: A molecule that blocks the active site, preventing the substrate from binding to the enzyme.
Catalyze: A verb meaning to speed up a reaction.
Catalyst: Another name for an enzyme or a substance that increases the rate of reaction.
Activation Energy: The specific amount of energy required to START a chemical reaction.
Energetics of Enzymatic Reactions
Activation Energy Analogy
Activation energy can be compared to the cost of buying a ticket to a movie.
When enzymes LOWER the activation energy, the reaction requires less energy to proceed, which is analogous to receiving a discount or finding a sale on that movie ticket.
Reaction Profiles (With vs. Without Enzymes)
Without Enzyme: The energy profile line is higher because a greater amount of energy is required for the reaction to occur.
With Enzyme: The energy profile line is lower because the enzyme facilitates the reaction using less energy.
General Outcome: Chemical reactions are catalyzed and happen significantly faster when enzymes are present.
Mechanisms of Substrate Binding
Specificity Requirements
Enzymes and their specific substrates must fit together precisely in order to function. Each enzyme is designed to fit only specific substrate.
Theories of Binding
Lock and Key Theory: This theory proposes that the active site of an enzyme is precisely shaped and rigid, holding specific substrates like a key fits into a specific lock.
Induced-fit Theory: This theory suggests that the active site and the substrate do not fit together perfectly at first; instead, both the enzyme and the substrate alter their shapes slightly upon contact to create a secure connection.
Factors Influencing Enzyme Function
Temperature
Enzymes function only within specific temperature ranges, and each individual enzyme has its own optimal range.
If the temperature becomes too extreme (either too high or too low), the enzyme will denature.
pH (Measure of Acidity)
Enzymes require specific pH ranges to maintain their activity.
Each enzyme has a unique optimal pH range.
Extreme pH levels will cause the enzyme to denature.
Enzyme Concentration
This refers to the total amount of enzyme present in a system.
A higher enzyme concentration typically results in faster chemical reactions.
Substrate Concentration
This refers to the total amount of substrate available for the enzyme to act upon.
A higher substrate concentration typically results in faster chemical reactions.
Denaturation
To denature means to permanently change the shape of the enzyme.
Once denatured, the enzyme will no longer work because the substrate can no longer bind to the physically altered active site.
Practice and Applications
True/False Concepts
Enzymes are an example of a protein: TRUE.
Enzymes decrease the rate of reaction: FALSE (they increase it).
Enzymes lower activation energy: TRUE.
Enzymes are substrate specific: TRUE.
Without enzymes present, a chemical reaction can still take place, just slower: TRUE.
Enzymes are only found in animals: FALSE (they are in all living things).
Case Study: Lactose Intolerance
Scenario: Delaney is lactose intolerant but enjoys ice cream. Consumption leads to digestive distress. She discovers that taking a probiotic daily for a few months helps her break down food at a faster rate without side effects.
Application: The probiotics Delaney is taking most likely contain the biomolecule Proteins (specifically the enzyme Lactase).
Graphical Analysis and Data Interpretation
Temperature Graphs: Used to identify the ideal temperature for enzyme function (the peak of the curve). If heated beyond a certain threshold (e.g., above ), the enzyme will denature.
pH Graphs: Different enzymes (e.g., Enzyme A vs. Enzyme B) will have different peaks representing their ideal pH levels. Extreme pH shifts lead to loss of function.
Substrate Concentration Graphs: Points on the graph with lower values (e.g., Point A) represent lower substrate concentrations. The rate of reaction is often highest at the plateau (e.g., Point C) because the enzymes are working at their maximum capacity given the available substrate or are saturated.