enzymes and digestion
🔹 What Are Enzymes?
Enzymes are biological catalysts – they speed up chemical reactions without being used up.
Made of proteins.
Each enzyme has a specific shape that fits the substance it works on – like a lock and key.
🔹 How Enzymes Work
The substrate fits into the enzyme’s active site.
The reaction happens, then the products are released.
This is called the lock and key model.
🔹 Factors Affecting Enzyme Activity
Factor | Effect |
|---|---|
Temperature | Enzymes work fastest at an optimum temperature (around 37°C in humans). If it's too hot, the enzyme denatures (the active site changes shape and doesn't work). |
pH | Each enzyme has an optimum pH. Too acidic or alkaline = enzyme may denature. |
Substrate concentration | More substrate = faster reaction (to a point), then levels off once all enzymes are working. |
🔹 Digestive Enzymes
Enzyme | Made in | Acts on | Breaks down into |
|---|---|---|---|
Amylase | Salivary glands, pancreas, small intestine | Starch | Sugars (e.g. maltose) |
Protease | Stomach (pepsin), pancreas, small intestine | Proteins | Amino acids |
Lipase | Pancreas, small intestine | Lipids (fats) | Fatty acids + glycerol |
🔹 Bile and Enzymes
Bile is made by the liver, stored in the gall bladder.
It’s not an enzyme but helps enzymes:
Emulsifies fats (breaks them into tiny droplets) → increases surface area for lipase.
Neutralises stomach acid → enzymes in the small intestine work best in alkaline conditions.
🔹 Required Practical: Investigating Enzyme Action
You need to know how to investigate how pH affects amylase:
Add starch solution and amylase to a test tube.
Use a water bath to control temperature.
Add iodine to spotting tiles to test for starch.
Take samples every 30 seconds.
Time how long it takes for iodine to stop turning blue-black (starch broken down).
Repeat with different pH buffers.
🔍 Purpose of Digestion
Breaks large, insoluble molecules into small, soluble ones that can be absorbed into the blood.
Enzymes speed up this process (biological catalysts).
🧠 Key Organs in the Digestive System
Organ | Function |
|---|---|
Mouth | Mechanical digestion (chewing), amylase in saliva starts breaking down starch. |
Oesophagus | Muscular tube that pushes food to the stomach. |
Stomach | Secretes protease enzyme (pepsin), hydrochloric acid (kills bacteria, gives optimum pH), churns food. |
Liver | Produces bile – neutralises stomach acid and emulsifies fats. |
Gall bladder | Stores bile. |
Pancreas | Produces enzymes (amylase, protease, lipase) and releases them into small intestine. |
Small intestine | Digestion finishes; nutrients absorbed into the blood. Villi increase surface area. |
Large intestine | Absorbs water from waste. |
🧪 Enzymes in Digestion
Enzyme | Where Made | Substrate | Products | Where It Works |
|---|---|---|---|---|
Amylase | Salivary glands, pancreas, small intestine | Starch | Sugars (e.g. maltose) | Mouth & small intestine |
Protease | Stomach (pepsin), pancreas, small intestine | Proteins | Amino acids | Stomach & small intestine |
Lipase | Pancreas, small intestine | Lipids (fats) | Fatty acids + glycerol | Small intestine |
🟡 Bile – What It Does
Made in liver, stored in gall bladder.
Not an enzyme, but helps digestion:
Emulsifies fats: breaks them into small droplets to increase surface area for lipase.
Neutralises stomach acid: makes conditions alkaline for enzymes in the small intestine.
🧪 Required Practical: Enzyme Activity
Investigate the effect of pH on amylase activity:
Add starch, amylase, and buffer solution to a test tube.
Keep in water bath at a constant temperature.
Every 30 seconds, take a sample and mix with iodine in a spotting tile.
If starch is present = blue-black.
Record time taken for iodine to stop changing colour.
🧠 Summary of Digestion
Food Type | Enzyme | Breakdown Products |
|---|---|---|
Carbohydrates | Amylase | Sugars (e.g. glucose) |
Proteins | Protease | Amino acids |
Fats | Lipase | Fatty acids + glycerol |