B2.5 Proteins - their functions and uses

Proteins have many functions, both inside and outside the cells of living organisms. Proteins, as enzymes, are now used widely in the home and in industry.

Proteins are made up from long chains of amino acids. These long chains are folded to produce a specific shape that enables other molecules to fit into the protein e.g. the biological catalysts we call enzymes.

Proteins act as:

• structural components of tissues such as muscles
• hormones
• antibodies
• catalysts

Catalysts increase the rate of chemical reactions. Biological catalysts are called enzymes. Enzymes are proteins. They enable the vast majority of reactions in cells, hence all the essential chemical reactions of any living organism.

The shape of an enzyme is vital for the enzyme’s function. High temperatures change the shape. 

Enzyme - Enzymes are very specific about what reactions they catalyse due to their shape. They are a specific sequence of amino acids

Substrate - There is a specific substrate for each enzyme. Its shape has to complement the enzymes ACTIVE SITE

Enzyme Substrate Complex - When the substrate binds with the active site and a reaction can take place

Products Made - The products no longer compliment the active site and are released. The enzyme is free to continue reacting.

The optimum is often around pH 7 neutral, which is the most common pH region inside cells.

Bile is made in the Liver, stored in the Gall Bladder and secreted by the bile duct into the small intestine.

Bile emulsifies fat, making fat, large droplets into small droplets. This increases the total surface area of fat droplets enabling lipase enzyme to work faster when digesting and break down the lipids. When the fat breaks down it becomes glycerol and fatty acids.

It also helps neutralise the acidic contents of the stomach as they enter the small intestine Otherwise small intestine enzymes would be denatured

Amylase

• It is made in the salivary glands, pancreas and small intestine
• It works in the mouth and small intestine
• It breaks down starch into sugar

Protease

• It's made in the salivary glands and small intestine
• It works in the stomach and small intestine
• It breaks down proteins into amino acids

Lipase

• It is made in the pancreas and small intestine
• It works in the small intestine
• It breaks down lipids into fatty acids and glycerol

We have acid in our stomach to help in digestion of proteins, minerals and carbohydrates. It activates digestive enzymes into amino acids because of acidic pH.
We need to digest food so it is small enough for the body to absorb its nutrients.

Some microorganisms produce enzymes that pass out of the cells. These enzymes have many uses in the home and in industry.

In the home:

• biological detergents may contain protein-digesting and fat-digesting enzymes (proteases and lipases)
• biological detergents are more effective at low temperatures (saving energy) than other types of detergents for breaking down plant and animal substances including blood, food and stains.

In the food industry:

• proteases are used to ‘pre-digest’ the protein in some baby foods to help digestion in immature digestive systems
• carbohydrases are used to convert starch into sugar syrup to sweeten foods
• isomerase is used to convert glucose syrup into fructose syrup, which is much sweeter and therefore can be used in smaller quantities in slimming foods and fizzy drinks.

In industry, enzymes are used to bring about reactions at normal temperatures and pressures that would otherwise require.

• Enzymes are excellent catalysts for speeding up reactions at relatively low temperatures and pressures without the need for increased energy costs of using high temperatures and more costly high pressure engineering in chemical manufacturing plants.

• They have the advantage of catalysing a specific reaction (no other reaction, no waste chemicals), lower energy costs, they can be recycled over and over again and any waste enzymes are biodegradable.

• There are a few disadvantages eg they are easily inhibited or denatured by changes in temperature and pH, so reaction conditions must be carefully controlled.