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.

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:

Lots of amino acid molecules → a protein molecule Glycine is an amino acid

Different proteinsThe 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) The particular shape that a protein molecule has allows other molecules to fit into it. This is particularly important for antibodies and enzymes.

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.

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.The animation shows how this works. In this example, two small molecules join together to make a larger one.

f 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.

emperature 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.

igestive enzymes 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. Enzymes Different enzymes catalyse different digestion reactions.Amylase   --->   Starch → sugarsProtease   --->   Proteins → amino acidsLipase      --->    Lipids → fatty acids + glycerolAmylase is an example of a carbohydrase. Lipids are fats and oils.

Different parts of the gut Different parts of the gut produce different enzymes. Where enzymes are produced Amylase    ----    Salivary glands, pancreas, small intestineProtease    ----    Stomach, pancreas, small intestineLipase       ----    Pancreas, small intestine

Summary Overall, this means that: 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 You should recall that different enzymes work best at different pH values. The digestive enzymes are a good example of this. Stomach acid 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. Bile 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 The names of the different types of enzymes usually end in the letters -ase. Three of the most common enzymes with their chemical actions are: lipase - breaks down fats protease - breaks down proteins carbohydrase - breaks down carbohydrates.

Enzyme uses Enzymes allow certain industrial processes to be carried out at normal temperatures and pressures, thereby reducing the amount of energy and expensive equipment needed. Enzymes are also used in the home, for example, in 'biological' detergents. examples...Protease                  -        Used to pre-digest proteins during the manufacture of baby foodsLipase    -   Used - together with protease - in biological detergents to break down (digest) the substances in stains into smaller, water soluble substancesCarbohydrase   -   Used to convert starch syrup, which is relatively cheap, into sugar syrup, which is more valuable - for example, as an ingredient in sports drinksIsomerase   -   Used to convert glucose syrup into fructose syrup - fructose is sweeter than glucose, so it can be used in smaller amounts in slimming foods

n industry, enzymes allow reactions that normally need expensive, energy-demanding equipment to happen at normal temperatures and pressures. On the other hand, most enzymes are denatured at high temperatures. Many enzymes are expensive to produce.

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Enzymes

Digestive Enzymes

Substances in Digestion

Enzymes in home and industry