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Explain the Importance of Enzymes in the Digestive System

Worksheet Overview

QUESTION 1 of 10

Did you know that our saliva contains something called enzymes? And did you know that without these enzymes digestion wouldn't be able to occur? So what are these enzymes anyway, and how do we use them in digestion?

Enzymes are proteins. They are biological catalysts that speed up a chemical reaction without being used up in the reaction. Enzymes have a specific shape that allows molecules to fit in - called the active site. It's here that large insoluble food substances are broken into smaller soluble molecules. Smaller molecules are easily absorbed by the blood. These smaller molecules might be used for different processes, for example, glucose can be used for respiration. Some smaller molecules will be used to build and make new products. Proteins can be broken down into peptides which are short chains of amino acids, and then further broken down into just amino acids. These amino acids can be used to build new proteins needed for growth and repair.

 

 

The lock and key theory 

The shape of the active site of an enzyme matches the shape of the food molecule (substrate), a bit like a key is specific to the lock it opens -  a substrate will only match a specific enzyme. This is called the lock and key theory. 

 

Image showing enzyme in action

 

Different types of food are broken down by different enzymes.  Digestive enzymes are classified by the type of food that they affect. There are three main types:

carbohydrase – breaks carbohydrate into smaller sugars

protease – breaks protein into amino acids

lipase – breaks fat into fatty acids and glycerol

 

Carbohydrates

Carbohydrates are chains of identical sugar molecules. The digestive enzyme called carbohydrase breaks the chemical bonds between the sugar molecules in each carbohydrate chain. An example is amylase. Amylase is found in saliva and pancreatic juices. Amylase breaks starch down into small sugar molecules called maltose. 

 

Image of starch broken into maltose by amylase enzyme

 

 

Proteins 

Proteins are made up of amino acids. There are over 20 different types of amino acids. Proteins are digested by digestive enzymes called proteases. These enzymes break proteins into smaller amino acids. They are found in the stomach, pancreas and small intestine.

 

Image of protein into amino acid by protease enzyme

 

 

Fats

Fats are digested in two stages:

Firstly, bile (made by the liver) allows the fat to ‘mix’ with water by breaking it into smaller droplets (emulsion). 

Secondly, the digestive enzyme lipase breaks each fat molecule into the smaller glycerol and fatty acid molecules. These can now be absorbed by the blood and can be used by the body for energy storage, and for building cell structures, such as cell membranes. Lipases are found in the pancreas and small intestine.

 

Image of fats being broken down by bile and enzyme lipase 

 

In the following activity, you will explain the importance of enzymes in the digestive system.

Enzymes are super important and without them digestion can't occur.

 

What are enzymes?

Enzymes break up larger food molecules into smaller food molecules. The lock and key theory is a model that describes how enzymes work. 

 

Describe the lock and key theory by matching up the sentences below.

 

Image showing enzyme in action

Column A

Column B

Enzymes have active sites that...
breakdown of the food molecule
The active site shape...
...have specific shapes
The fit between the enzyme and substrate is like.....
matches the shape of specific food molecules
The enzyme catalyses the...
a lock and key

Enzymes are very specific. They have active sites that only bind with specific food molecules, also known as substrates.

 

Match up the types of enzymes with their substrates.

Column A

Column B

Carbohydrase
Breaks fat into fatty acids and glycerol
Protease
Breaks carbohydrate into smaller sugars
Lipase
Breaks protein into amino acids

Starch is a carbohydrate. In the image below, starch is being broken down by an enzyme, forming simple sugar molecules.

 

Label (a) and (b).

 

Image showing starch being broken down into maltose

(a) Lipase

(a) Amylase

(b) Glucose

(b) Maltose

Enzymes break down larger insoluble food molecules to smaller soluble food molecules. Starch is a carbohydrate that will often get broken down into glucose.

 

What might we need glucose for? 

To make enzymes

Photosynthesis

Respiration

Digestive enzymes are essential for digestion to occur.

 

Where are the main enzymes found and what do they digest? 

The image below shows an enzyme catalysing a substrate. The enzyme has an active site.

 

What is special about the active site? 

 

Image showing enzyme in action

 

The active site is very specific

The active site is not specific

The active site will allow any substrate to fit

The active site will only fit complementary substrates

The image below shows the digestion of fats.

 

Why is bile added to the fat? 

 

Image of fats being broken down by bile and enzyme lipase

 

Bile emulsifies fat, allowing lipase to break fat molecules up quicker

Bile is an enzyme and breaks up the fat completely

Bile mixes with the fat to make it easier for the fat to travel in the blood

We often eat protein as part of a balanced diet.

 

What happens to this protein once we have eaten it? 

 

Image of foods high in protein

The protein is broken down in fatty acids

The protein is broken down by proteases into amino acids

The amino acids are recombined to make new types of proteins

The amino acids are recombined to make new carbohydrates

The image below shows proteins being catalysed by proteases into amino acids.

 

Where in the body does this process occur? 

 

Image of protein into amino acid by protease enzyme

Stomach

Small intestine

Large intestine

Pancreas

  • Question 1

Enzymes are super important and without them digestion can't occur.

 

What are enzymes?

CORRECT ANSWER
EDDIE SAYS
Did you manage to get all the blanks filled in correctly here? This is a key aspect of the topic of digestion, so you need to make sure you understand what enzymes are and why they are important. A common misconception is that enzymes get used up in reactions. Enzymes help to speed up reactions but don't take part in the actual reaction, so don't get used up.
  • Question 2

Enzymes break up larger food molecules into smaller food molecules. The lock and key theory is a model that describes how enzymes work. 

 

Describe the lock and key theory by matching up the sentences below.

 

Image showing enzyme in action

CORRECT ANSWER

Column A

Column B

Enzymes have active sites that...
...have specific shapes
The active site shape...
matches the shape of specific foo...
The fit between the enzyme and su...
a lock and key
The enzyme catalyses the...
breakdown of the food molecule
EDDIE SAYS
Don't worry if you found this one a bit tricky - one tip is to look at the sentence structure and you might well be able to see that there's only one way that they will all make sense! Enzymes, and the specific food molecules they help to break down, fit together - a little like a puzzle piece or a lock and key. It isn't possible for an enzyme to work if it doesn't fit exactly on to a specific food molecule.
  • Question 3

Enzymes are very specific. They have active sites that only bind with specific food molecules, also known as substrates.

 

Match up the types of enzymes with their substrates.

CORRECT ANSWER

Column A

Column B

Carbohydrase
Breaks carbohydrate into smaller ...
Protease
Breaks protein into amino acids
Lipase
Breaks fat into fatty acids and g...
EDDIE SAYS
A very important bit of information this!! You need to make sure you know it. To help you remember the name of these enzymes and their substrates - the clue is in the name: Carbohydrase → Carbohydrates Protease → Proteins Lipase → Lipids (another name for fats)
  • Question 4

Starch is a carbohydrate. In the image below, starch is being broken down by an enzyme, forming simple sugar molecules.

 

Label (a) and (b).

 

Image showing starch being broken down into maltose

CORRECT ANSWER
(a) Amylase
(b) Maltose
EDDIE SAYS
Well done if you got both of these right - it was a bit of a challenge! A good tip to remember is that most enzymes will end in the letters -'ase'. For example: amylase peptidase lipase The enzyme amylase breaks down carbohydrates to make maltose.
  • Question 5

Enzymes break down larger insoluble food molecules to smaller soluble food molecules. Starch is a carbohydrate that will often get broken down into glucose.

 

What might we need glucose for? 

CORRECT ANSWER
Respiration
EDDIE SAYS
Digestion allows smaller molecules to be used by the body for important processes. Often, these smaller glucose molecules will be used to build new carbohydrates. The most important use for this glucose is in the process of respiration in which glucose is converted into energy.
  • Question 6

Digestive enzymes are essential for digestion to occur.

 

Where are the main enzymes found and what do they digest? 

CORRECT ANSWER
EDDIE SAYS
This activity is a great summary for revision purposes. How did you get on with it? You can always try this question a few times to consolidate your knowledge.
  • Question 7

The image below shows an enzyme catalysing a substrate. The enzyme has an active site.

 

What is special about the active site? 

 

Image showing enzyme in action

 

CORRECT ANSWER
The active site is very specific
The active site will only fit complementary substrates
EDDIE SAYS
Active sites have a specific shape that is complementary to a particular substrate. Like a puzzle piece, the substrate and the active site have to be complementary or the substrate won't be broken down.
  • Question 8

The image below shows the digestion of fats.

 

Why is bile added to the fat? 

 

Image of fats being broken down by bile and enzyme lipase

 

CORRECT ANSWER
Bile emulsifies fat, allowing lipase to break fat molecules up quicker
EDDIE SAYS
How did you do with this one? They all sounded plausible at first glance, didn't they? Bile isn't an enzyme. It emulsifies the fat, breaking it up into smaller droplets. This gives the fat droplets a larger surface area, which helps lipase to catalyse it quicker. Bile also neutralises food substances leaving the acidic conditions of the stomach, creating an alkaline environment so that the lipase can work at its optimum pH level.
  • Question 9

We often eat protein as part of a balanced diet.

 

What happens to this protein once we have eaten it? 

 

Image of foods high in protein

CORRECT ANSWER
The protein is broken down by proteases into amino acids
The amino acids are recombined to make new types of proteins
EDDIE SAYS
There were two options correct in this question. The protein that we eat is broken down by proteases into amino acids, which are then recombined to create new proteins. It's important to eat a variety of protein, as different sources of protein will be made up of different kinds of amino acids. These amino acids will be used for growth and repair in our body.
  • Question 10

The image below shows proteins being catalysed by proteases into amino acids.

 

Where in the body does this process occur? 

 

Image of protein into amino acid by protease enzyme

CORRECT ANSWER
Stomach
Small intestine
Pancreas
EDDIE SAYS
Did you get all three options this time? The breaking down of proteins starts to take place in the stomach, but continues in the small intestines and the pancreas. Different types of proteases break down different types of proteins. Some proteases break proteins into peptides (shorter amino acid chains) first, before further breaking them down into amino acids. You've reached the end of this activity - how do you feel about this topic now?
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