Have you ever put a piece of white bread in your mouth and left it there? Without chewing or swallowing, the bread will slowly begin to dissolve, producing a sweet taste. This happens because of the salivary enzyme amylase. Amylase function is to break down the complex carbohydrates in the bread and turns them into smaller, sweet-tasting sugar molecules.
The Definition of Amylase
First things first, what is amylase? It is a protein made by the salivary glands in and around the mouth of humans, where it triggers the process of digestion. Amylase is classified as an enzyme as it helps the body to catalyse the hydrolysis of carbohydrates into sugars.
Amylase is a digestive enzyme that speeds up the breakdown of starch into maltose.
Hydrolysis is the process of splitting a compound using water.
Amylase is also produced in the pancreas, where dietary starch is further broken down into simple sugars. These sugars are then further converted by the body (by other enzymes) into energy in the form of glucose.
Plants, along with some types of bacteria, produce amylase too.
Amylase is an Enzyme
Amylase is an enzyme. Enzymes are specialised proteins that speed up chemical reactions (in this case, digestion) by acting as biological catalysts.
Learn more about Enzymes by checking out our article!
Amylase breaks down starch (a long-chain saccharide) into smaller sugars such as maltose. It does this using a water molecule to break the glycosidic bonds in the starch compound.
A catalyst is a substance that increases the rate of reaction without being used up.
A glycosidic bond is a type of covalent bond that links sugars together.
Enzymes help to increase the rate of reaction by lowering the activation energy of a reaction.
The activation energy is the minimum energy required for a chemical reaction.
The feasibility of a reaction typically relies on a high temperature. So that reactions can take place at lower temperatures, enzymes reduce the amount of activation energy required - this increases the rate of reaction.
Enzymes are three-dimensional globular proteins. Every enzyme has a specific active site. This is where a specific substrate (the interacting substance) binds to the enzyme.
Think of an enzyme as a lock and the substrate as a key. Only a specific 'key' (substrate) can 'open' (interact with) the enzyme.
Every enzyme has an optimum temperature and pH where it functions best.
Outside these conditions, the enzymes can become denatured. The bonds that maintain the protein's shape break, and the enzyme will no longer function properly. But a denatured enzyme isn't a problem for the body. If an enzyme becomes denatured, the body will synthesise more.
The Structure of Amylase
Amylase is a globular protein. First, let's recap the four categories of protein structure:
- Primary proteins - the sequence of amino acids in a polypeptide chain determines the primary structure of a protein.
Amino acids are organic acids that contain:
- a carboxyl functional group (-COOH)
- an amine functional group (-NH2)
- a side chain specific to the amino acid (-R)
Amino acids commonly act as monomers, small units of larger molecules. Linking a few amino acids together creates a peptide. A large chain containing numerous amino acids is a polypeptide.
- Secondary proteins - hydrogen bonds form between the amino acids in the chains, altering the shape.
- There are two types of secondary proteins: spiral alpha-helix shapes and folded beta-sheets.
- Tertiary proteins - the protein bends and folds from a secondary protein into a complex, three-dimensional shape.
- Quaternary proteins - these proteins are made of different polypeptide chains.
Amylase, like all human enzymes, is a tertiary protein. It has some special structural traits that help it carry out its role effectively.
It has a globular (roughly spherical) shape. Tightly folded polypeptide chains cause these globular shapes. This shape allows amylase to form an active site where the substrate molecule can bond.
The outside of the amylase enzyme contains hydrophilic (water-loving) groups that make it soluble. This allows amylase to be easily transported around the body.
The Function of Amylase
Amylase catalyses the breakdown of starch molecules (polysaccharides) into maltose molecules (disaccharides) - but how does it do that?
The amylase enzyme collides with starch molecules and forms an enzyme-substrate complex. Amylase allows the starch molecule to break down into many smaller maltose molecules. The maltose molecules are released, and the enzyme is free to act again.
A polysaccharide is a large carbohydrate molecule, made up of lots of sugar molecules.
A disaccharide is a sugar molecule made up of two glucose units.
Amylase supports digestion in the mouth and the pancreas. Breaking down large, complex carbohydrates into smaller sugars makes it easier for the body to digest them and gain the energy they provide.
Sources of complex carbohydrates include bread, pasta, potatoes, and rice.
Fig. 1 - Complex carbohydrates are an essential part of our diets. They provide energy for our bodies and brains, aid with digestion, and may reduce our risk of heart disease, unsplash.com
Maltose molecules are made of only two glucose units; the body can break them down quickly to form single glucose molecules. Glucose molecules are the body's primary source of energy from food.
Amylase is the primary component of saliva. But saliva doesn't just help us digest our food – it also plays a vital role in looking after our teeth. Saliva neutralises acids, prevents plaque build-up and kills bacteria.
Amylase Testing with an Example
It's normal to have a small amount of amylase in your blood and urine.
The healthy range of amylase in the blood is 30 to 110 units per litre.
In urine, it's 2.6 to 21.2 international units per hour.
If your amylase levels are outside the usual range, you may be experiencing a health problem. High amylase levels typically indicate an issue with your pancreas. Low amylase levels suggest problems with your pancreas, liver, or kidneys. Low levels can also indicate cystic fibrosis.
Cystic fibrosis is a genetic disease occurring in 0.04% of the population (equivalent to 1 in every 2500 people). It is a multi-system disease affecting the pancreas, intestines, reproductive tract and lungs. Sufferers find it challenging to absorb adequate nutrients, leading to fatigue-related problems.
Amylase tests can be used to diagnose or monitor several diseases, such as:
How is an Amylase Test Conducted?
Amylase is an enzyme that increases the rate of starch digestion. Like all enzymes, amylase functions best at a specific temperature and pH.
During your GCSEs, you will carry out an experiment to see how pH affects the rate of reaction of amylase.
Method:
Set up test tubes at different pHs by using a buffer solution.
Add amylase and starch to each test tube, then add a drop of iodine solution. Iodine turns blue-black in the presence of starch.
When the iodine has returned to its natural orange colour, all the starch has been broken down into maltose.
Use a stopwatch to time how long it takes for the iodine solution to change colour — the quicker the colour change, the faster the rate of reaction.
Control Variable
Enzymes are affected by pH and temperature. We only want to test the effect of pH, so the temperature should stay the same. It can be controlled using a water bath or electric heater to keep the test tubes at 35°C.
Risk Assessment
Results
Present your results in a table. Calculate the rate of starch breakdown using the following equation: 1 / time in seconds
Finally, plot a graph of the rate of reaction against pH.
| pH | Time taken for starch to break down (seconds) | Rate of starch breakdown (1/t) |
| 5 | 85 | 0.012 |
| 6 | 30 | 0.033 |
| 7 | 25 | 0.040 |
| 8 | 40 | 0.025 |
| 9 | 100 | 0.010 |
Table 1: rate of starch breakdown by amylase (based on time taken) for different pH conditions.
Fig. 2 - The rate of reaction of amylase against pH value.
Amylase - Key takeaways
Amylase is a digestive enzyme that catalyses the breakdown of starch into maltose. It is produced in the salivary glands and the pancreas.
Enzymes are biological catalysts. They speed up the rate of chemical reactions without being used up.
Amylase has a globular shape and hydrophilic groups on the outside that make the enzyme soluble.
Amylase plays an essential role in digestion. It breaks down complex carbohydrates into smaller, simple sugars, making them more accessible for the body to digest. Salivary amylase also supports dental health.
Abnormal amylase levels in blood or urine can indicate a health problem - especially those that affect the pancreas.
References
- Anne Marie Helmenstine, Amino Acid Definition and Examples, ThoughtCo, 2019
- CGP, AQA A-Level Biology Revision Guide, 2015
- Cleveland Clinic, Amylase Test, 2022
- David J. Culp, Murine Salivary Amylase Protects Against Streptococcus mutans-Induced Caries, Frontiers in Physiology, 2021
- Edexecel, Salters-Nuffield Advanced Biology, 2015
- Keith Pearson, What Are the Key Functions of Carbohydrates?, Healthline, 2017
- Regina Bailey, Salivary Amylase and Other Enzymes in Saliva, ThoughtCo, 2019
- Fig. 1. Image (https://unsplash.com/es/fotos/m5Ft3bsalhQ) by Bozhin Karaivanov, free use under Unsplash license.
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