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[h] iGCSE Biology Notes Enzymes
[q] Enzymes
What are enzymes and what do they do?
[a]
- Enzymes are proteins that function as biological catalysts.
- This means they make a chemical reaction faster and/or lower the activation energy needed for a reaction
- Examples of these reactions include digestive reactions that break down large food molecules into smaller, soluble nutrients
[q] How do enzymes work?
How do enzymes catalyse reactions?
[a]
- Enzymes work using the ‘lock and key’ model
- This is where the active site of the enzyme must be a complimentary shape to the substrate it binds to
- Once they bind, they become an enzyme-substrate complex.
- Then, the products are formed
- Only one substrate can fit into each enzyme, so they are specific
[q] What enzymes are there?
Which enzymes do you need to know?
[a]
- You need to know the three major digestive enzymes that we use to break down our food.
- This process is really important, because molecules like protein, starch and lipids can not be absorbed as they are large and insoluble.
- Therefore, enzymes in our alimentary canal break down these molecules into smaller and soluble nutrients, which can be absorbed.
HUMAN DIGESTIVE SYSTEM
[q] What enzymes are there?
Which enzymes do you need to know?
[a]
- The first enzyme is amylase. It breaks down starch into simpler sugars. More specifically, it breaks it into maltose. (There is a maltase enzymes that breaks this down into glucose). Amylase is produced in the salivary glands, small intestine and the pancreas
- Lipase breaks down lipids into one glycerol and three fatty acids each. It is produced in the pancreas, small intestine and pancreas
- Proteases break down proteins into amino acids. Proteases are produced in the stomach, pancreas and small intestine
HUMAN DIGESTIVE SYSTEM
[q] What can affect enzyme activity?
How does temperature effect enzyme activity?
[a]
- Anyone know how temperature affects enzyme activity?
- At higher temperatures, the enzyme and substrate particles have more kinetic energy as they move and vibrate more, so there will be more successful collisions and the reaction will be faster.
- However, if the temperature gets too high, it can change the shape of the enzyme’s active site, making it denatured. This means the substrate is no longer a complimentary shape and can no longer fit.
[q] What can affect enzyme activity?
How does pH effect enzyme activity?
[a]
- Anyone know how pH affects enzymes activity?
- Each type of enzyme has an optimum pH, which is the pH it works best at and gives the highest rate of reaction.
- If the pH strays too far from the optimum (too high or too low), this can also change the shape of the enzyme’s active site and make it denatured. Again, this means the substrate is no longer a complimentary shape and it will no longer fit.
[q] How have we adapted for digestion?
How have we adapted for digestion?
[a]
- The stomach is full of hydrochloric acid, around pH 2. This is because the protease that works in the stomach, called pepsin, has an optimum pH of 2.
- However, the protease in the small intestine, trypsin, has an optimum pH of 7. This is why bile, an alkali, is produced by the liver and secreted into the small intestine to neutralize the stomach acid.
- Also never forget, the small intestine has lots of villi to increase the surface area for very fast absorption of these nutrients
[q] Specific Enzymes
What specific enzymes do humans have?
[a]
- Pepsin is a protease found in the stomach that digests protein into amino acids. It’s optimum pH is pH 2 since the stomach contain hydrochloric acid
- Trypsin is another protease which also digests protein into amino acids but this time found in the small intestine, so the optimum pH is 8
- Maltase breaks down maltose into glucose in the small intestine. (Maltose is produced when amylase breaks down starch)
[q] One more use for enzymes
Are enzymes just used for digestion?
[a]
- Enzymes are not just used for digestion
- There is pretty much one enzyme for every chemical reaction that happens in your body (which is a lot)
- One example you need to know are the enzymes in sperm cells.
- Sperm cells have an organelle in the head called an acrosome which contains enzymes to break down the wall of the egg.
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