Proteins and Enzymes
What are Proteins?Proteins are made from long chains of smaller molecules called amino acids. These long chains are folded into particular shapes. This is important in relation to how antibodies and enzymes work. What are enzymes? Enzymes are biological catalysts. There are optimum temperatures and pH values at which their activity is greatest. Enzymes are also proteins. If the shape of an enzyme changes, it may no longer work (it is said to have been 'denatured').
- Amino acids to proteins: Proteins are polymers. They are built up in cells when monomers called amino acids join together end to end. There are only about 20 different naturally occurring amino acids. However, each protein molecule has hundreds, or even thousands, of them joined together in a unique sequence. This gives each protein its own individual properties. Different proteins: The long chains of amino acids fold to give each type of protein molecule a specific shape. Proteins act as:
- Structural components of tissues (such as muscles)
- Hormones (such as insulin)
- Antibodies (part of the body's immune system)
- Biological catalysts (enzymes)
How enzymes work
Enzymes are biological catalysts - substances that increase the rate of chemical reactions without being used up.
Enzymes are proteins folded into complex shapes that allow smaller molecules to fit into them. The place where these substrate molecules fit is called the active site.
If the shape of the enzyme changes, its active site may no longer work. We say the enzyme has been 'denatured'.
Enzymes can be denatured by high temperatures or extremes of pH. Note that it is wrong to say the enzyme has been killed. Although enzymes are made by living things, they are proteins and not alive. - ENZYMES CAN'T DIE
Temperature, pH and enzymes
Temperature and enzymes
As the temperature increases, so does the rate of reaction. But very high temperatures denature enzymes.
The graph shows the typical change in an enzyme's activity with increasing temperature. The enzyme activity gradually increases with temperature up to around 37ºC, or body temperature. Then, as the temperature continues to rise, the rate of reaction falls rapidly as heat energy denatures the enzyme.
pH and enzymes
Changes in pH also alter an enzyme’s shape. Different enzymes work best at different pH values. The optimum pH for an enzyme depends on where it normally works. For example, intestinal enzymes have an optimum pH of about 7.5. Enzymes in the stomach have an optimum pH of about 2.
The enzymes involved in respiration, photosynthesis and protein synthesis work inside cells. Other enzymes are produced by specialised cells and released from them. The digestive enzymes are like this. They pass out into the gut, where they catalyse the breakdown of food molecules.
- Amylase catalyses the breakdown of starch into sugars in the mouth and small intestine
- Proteases catalyse the breakdown of proteins into amino acids in the stomach and small intestine
- Lipases catalyse the breakdown of fats and oils into fatty acids and glycerol in the small intestine
Other substances in digestion
The stomach produces hydrochloric acid. This helps to begin digestion, and it kills many harmful microorganisms that might have been swallowed along with the food. The enzymes in the stomach work best in acidic conditions - in other words, at a low pH.
After the stomach, food travels to the small intestine. The enzymes in the small intestine work best in alkaline conditions, but the food is acidic after being in the stomach. A substance called bile neutralises the acid to provide the alkaline conditions needed in the small intestine. Bile is produced by the liver and stored in the gall bladder.
Enzymes in the home and industry
Enzyme names + uses
The names of the different types of enzymes usually end in the letters -ase. Three of the most common enzymes with their chemical actions + uses are:
- lipase- breaks down fats = Used - together with protease - in biological detergents to break down (digest) the substances in stains into smaller, water soluble substances
- protease- breaks down proteins = Used to pre-digest proteins during the manufacture of baby foods
- carbohydrase- breaks down carbohydrates. = Used to convert starch syrup, which is relatively cheap, into sugar syrup, which is more valuable - for example, as an ingredient in sports drinks