Enzymes & Biological Catalysts
Enzymes are biological catalysts made of folded protein chains that speed up metabolic reactions in living cells without being used up. Each enzyme has a specifically shaped active site complementary to its substrate, and its rate of activity depends on temperature, pH, and substrate concentration.
- Catalyst
- A substance that increases the rate of a chemical reaction without being changed or used up.
- Active site
- The specific region of an enzyme where the substrate binds.
- Substrate
- The molecule that an enzyme acts upon.
Enzymes & Biological Catalysts: Enzyme Collision, Active Site & Rate Curve Lab
Drag the temperature, pH, and substrate sliders to watch how kinetic collisions, active-site binding, and denaturation change the reaction rate in real time.
Key Concepts & Exam Definitions (5)
- Catalyst
- A substance that increases the rate of a chemical reaction without being changed or used up.
- Active site
- The specific region of an enzyme where the substrate binds.
- Substrate
- The molecule that an enzyme acts upon.
- Denaturation
- The irreversible change in shape of an enzyme's active site, caused by extreme pH or temperature.
- Optimum
- The specific condition (e.g., temperature or pH) at which an enzyme works best.
Quick-Fire Flashcards (5)
Click any card to check the answer, then mark it as Known to track your progress.
What are enzymes made of?
What happens when an enzyme denatures?
What is an enzyme-substrate complex?
Why are enzymes specific?
What is the effect of too high or low pH on an enzyme?
Exam-Style Questions & Mark Schemes (3)
Write or think through your answer first, then click Check Mark Scheme to see the exact points examiners award marks for.
- Q1
Explain why enzymes are essential for living organisms.
Click “Check Mark Scheme” to compare your answer, They speed up metabolic reactions to a rate that can sustain life; without them, reactions would be too slow.
- Q2
Describe the effect of increasing substrate concentration on enzyme activity.
Click “Check Mark Scheme” to compare your answer, The rate increases as more substrate molecules collide with active sites, until all active sites are occupied (saturation), then the rate levels off.
- Q3
Why do digestive enzymes have different optimum pH levels?
Click “Check Mark Scheme” to compare your answer, Because different parts of the digestive system have different pH levels (e.g., stomach is acidic, small intestine is alkaline), so enzymes must be adapted to work best in their specific location.
Common Exam Questions (3)
What is an enzyme?
An enzyme is a biological catalyst made of protein. It lowers the activation energy of a specific chemical reaction inside cells so the reaction proceeds rapidly at body temperature, without the enzyme itself being changed or used up.
How does temperature affect enzyme action?
As temperature rises toward the optimum (around 37°C in humans), molecules gain kinetic energy and collide more frequently, increasing the rate of reaction. Above the optimum temperature, thermal vibrations break bonds holding the protein together, so the active site changes shape (denatures) and can no longer bind the substrate.
What is the lock and key model?
The lock and key model explains enzyme specificity: the substrate has a shape that is complementary to the enzyme's active site, fitting into it to form an enzyme-substrate complex just as a specific key fits a lock.
Need more questions on Enzymes & Biological Catalysts, or want to organise your own notes?
Type a specific exam question you are stuck on, pick one of the prompts below, or paste your class notes to build a custom set of flashcards and practice questions on this page.
Related study guides
Animal & Plant Cell Structure
All living organisms are composed of cells. Plant and animal cells are eukaryotic (containing a membrane-bound nucleus and organelles), whereas bacterial cells are prokaryotic and carry their DNA free in the cytoplasm as a single circular chromosomal loop and small rings called plasmids.
Aerobic & Anaerobic Respiration
Cellular respiration is an exothermic chemical reaction that occurs continuously in all living cells to transfer energy from glucose for metabolic processes. Respiration takes place aerobically (using oxygen in the mitochondria to release a large amount of energy) or anaerobically when oxygen is in short supply.
Cellular Respiration: Steps & Stages
Aerobic cellular respiration breaks down glucose through four linked stages: glycolysis in the cytoplasm, followed by the link reaction, the Krebs cycle, and oxidative phosphorylation via the electron transport chain inside the mitochondria. Learning where each stage occurs, what enters and leaves, and how reduced NAD and FAD drive ATP synthesis makes every exam question on respiration straightforward.