List digestive enzymes and their substrates
WHAT is a digestive enzyme?
The name usually tells you the substrate + the suffix -ase:
- Amylase → acts on amylum (starch)
- Protease → acts on proteins
- Lipase → acts on lipids (fats)
- Nuclease → acts on nucleic acids
The Four Substrate Families (80/20 core)
There are only four food macromolecules to worry about. Learn the enzyme for each, where it works, and what it makes.
1. Carbohydrates (starch → glucose)
| Enzyme | Made by | Site | Substrate → Product |
|---|---|---|---|
| Salivary amylase (ptyalin) | Salivary glands | Mouth | Starch → maltose |
| Pancreatic amylase | Pancreas | Small intestine | Starch → maltose |
| Maltase | Small intestine | Small intestine | Maltose → glucose + glucose |
| Sucrase | Small intestine | Small intestine | Sucrose → glucose + fructose |
| Lactase | Small intestine | Small intestine | Lactose → glucose + galactose |
2. Proteins (protein → amino acids)
| Enzyme | Made by | Site | Substrate → Product |
|---|---|---|---|
| Pepsin | Stomach (gastric glands) | Stomach | Proteins → peptides |
| Trypsin | Pancreas | Small intestine | Proteins/peptides → smaller peptides |
| Chymotrypsin | Pancreas | Small intestine | Proteins/peptides → smaller peptides |
| Peptidases (erepsin) | Small intestine | Small intestine | Peptides → amino acids |
3. Fats (lipids → fatty acids + glycerol)
| Enzyme | Made by | Site | Substrate → Product |
|---|---|---|---|
| Lingual lipase | Tongue glands | Mouth/stomach | Fats → fatty acids + glycerol (small amount) |
| Pancreatic lipase | Pancreas | Small intestine | Emulsified fats → fatty acids + glycerol |
4. Nucleic acids
| Enzyme | Made by | Site | Substrate → Product |
|---|---|---|---|
| Nucleases (DNase, RNase) | Pancreas | Small intestine | DNA / RNA → nucleotides |
HOW to reconstruct the whole table from scratch (Derivation logic)
You don't memorise 15 rows — you derive them from 3 rules:
- Every polymer needs a starter + a finisher. Big cuts happen early (mouth/stomach), final cuts into monomers happen in the small intestine.
- Match enzyme optimum pH to the organ. Acid stomach ⇒ pepsin/lingual lipase. Neutral/alkaline intestine ⇒ pancreatic + intestinal enzymes.
- Pancreas = the master gland. It secretes one of each type: amylase, trypsin/chymotrypsin, lipase, nucleases — all into the small intestine.
Common Mistakes (Steel-manned)
Recall
Recall Flashcards — reveal after you try
#flashcards/biology Which enzyme digests starch in the mouth? ::: Salivary amylase (ptyalin), starch → maltose Final product of maltase acting on maltose? ::: Two glucose molecules Enzyme that digests protein in the stomach and its optimum pH? ::: Pepsin, optimum pH ~2 (acidic) Two pancreatic proteases? ::: Trypsin and chymotrypsin Enzyme that digests fats and what must happen first? ::: Lipase; bile must emulsify the fat first Products of complete fat digestion? ::: Fatty acids + glycerol Sucrase splits sucrose into? ::: Glucose + fructose Lactase splits lactose into? ::: Glucose + galactose Which enzyme type digests DNA/RNA and where? ::: Nucleases (DNase/RNase), from pancreas, in small intestine Is bile an enzyme? ::: No — it is an emulsifier/detergent, not a catalyst The general chemical reaction of all digestion is called? ::: Hydrolysis (splitting bonds using water) Which gland secretes one enzyme of every food type? ::: The pancreas
Recall Feynman: explain to a 12-year-old
Imagine your food is made of long LEGO chains — too big to fit through the tiny doors in your gut wall. Digestive enzymes are little scissor-workers. Amylase snips starch chains, pepsin and trypsin snip protein chains, lipase snips fat, and nucleases snip DNA. Each worker only cuts its own kind of chain. They each dip the chain in water to break a link (that's hydrolysis). Bile isn't a scissor — it's like soap that breaks a big grease blob into tiny drops so the fat-scissors can reach it. Once everything is snipped into single LEGO bricks (glucose, amino acids, fatty acids), they slip through the doors into your blood.
Connections
- Hydrolysis and Condensation Reactions — the chemistry behind every -ase
- Enzyme Action and Optimum pH — WHY pepsin ≠ trypsin location
- Structure of the Small Intestine — where final digestion & absorption occur
- Bile and Emulsification — the non-enzyme helper
- Absorption of Nutrients — what happens to the monomers next
- Pancreas and its Secretions — the master enzyme gland
Concept Map
Hinglish (regional understanding)
Intuition Hinglish mein samjho
Dekho, humara khana bade-bade molecules se bana hota hai — starch, protein, fat, aur DNA. Ye itne bade hote hain ki gut ki wall ke andar absorb hi nahi ho sakte. Isliye body ko chahiye digestive enzymes, jo ek tarah ki "biological scissors" hain. Ye bade polymers ko chhote monomers mein kaat dete hain, aur har cut mein ek water molecule use hota hai — is process ko hydrolysis kehte hain.
Yaad rakhne ka smart tareeka: sirf 4 food families hain. Carbohydrate ko amylase (mouth se shuru, pancreas se finish, phir maltase glucose banata hai). Protein ko stomach mein pepsin (acidic pH ~2 pe kaam karta hai), aur small intestine mein trypsin/chymotrypsin, phir peptidases amino acids bana dete hain. Fat ko lipase todta hai — lekin pehle bile aata hai jo enzyme nahi hai, wo sirf emulsifier (soap jaisa) hai jo fat ki badi bund ko chhoti droplets mein todta hai taaki lipase easily attack kar sake. DNA/RNA ko nucleases todte hain.
Ek golden rule: pancreas ek "master gland" hai — wo har type ka ek enzyme deta hai (amylase, protease, lipase, nuclease), sab small intestine mein. Aur enzyme kahan kaam karega, wo optimum pH decide karta hai — pepsin ko acid chahiye (stomach), trypsin ko alkaline (intestine). Isliye exam mein "-ase" naam dekh ke substrate guess kar lo: amyl-ase = starch, prote-ase = protein, lip-ase = fat. Ye trick 80% questions cover kar leti hai!