11a Bilegdemberel

ENZYME ACTIVITY

ACTIVE SITE• Enzymes are globular proteins. In one part of the molecule, there is an area called the

active site, where the substrate molecule can bind. This produces an enzyme-substrate complex. The 3D shape of the active site fits the substrate perfectly, so only one type of substrate can bind with the enzyme. The enzyme is specific for that substrate

ENZYMES• An enzyme is a protein that acts as a biological catalyst--- that is, it speeds up a

metabolic reaction without itself being permanently changed.

• The substrate present at the start of an enzyme-catalysed reaction is called the substrare. The product is the new substance or substances formed.

• Virtually every metabolic reaction which takes place within a living organism is catalysed by an enzyme. Many enzyme names end in –ase, for example amylase.

• Enzymes are globular proteins. Like all globular proteins, enzyme molecules are coiled into a precise three-dimensional shape, with hydrophillic r groups (side chains) on the outside of the molecule ensuring that they are soluble.

ACTIVATION ENERGY• Substrates generally need to be supplied with energy to cause them to change into

products. The energy required to do this is called activation energy.

• Enzymes are able to make substances react even at low temperatures. They reduce the activation energy needed to make the reaction takes place. They do this by distorting the shape of the substrate molecule when binds at the enzyme’s active site

EFFECT OF PH

• Enzymes are affected by changes in pH. The most favorable pH value - the point where the enzyme is most active - is known as the optimum pH.

• Extremely high or low pH values generally result in complete loss of activity for most enzymes. pH is also a factor in the stability of enzymes. As with activity, for each enzyme there is also a region of pH optimal stability.

Enzyme pH Optimum

Lipase (pancreas) 8.0

Lipase (stomach) 4.0 - 5.0

Lipase (castor oil) 4.7

Pepsin 1.5 - 1.6

Trypsin 7.8 - 8.7

Urease 7.0

Invertase 4.5

Maltase 6.1 - 6.8

Amylase (pancreas) 6.7 - 7.0

Amylase (malt) 4.6 - 5.2

Catalase 7.0

TEMPERATURE• Like most chemical reactions, the rate of an enzyme catalysed reaction increases as the

temperature is raised

• Above a certain temperature, however, hydrogen bonds holding the enzyme molecule in shape begin to break. This causes the tertiary structure of the enzyme to change, an effect called denaturatio. This affects the shape of its active site. It becomes less likely that the substrate molecule will be able to bind with the enzyme, and the rate of reaction slows down

ENZYME CONCENTRATION• The greater the concentration of enzyme, the more frequent the collisions between

enzyme and substrate, and therefore the faster the rate of the reaction. However, at very high enzyme concentrations, the concentration of substrate may become a limiting factor, so the rate does not continue to increase if the enzyme concentration is increased

SUBSTRATE CONCENTRATION• The greater the concentration of substrate, the more frequent the collisions between

enzyme and substrate, and therefore the faster the rate of the reaction. However, at high substrate concentration, the concentration of enzyme may become a limiting factor, so the rate does not continue to increase if the substrate concentration is increased..

COENZYMES• A nonproteinaceous organic substance that usually contains a vitamin or mineral and

combines with a specific protein, the apoenzyme, to form an active enzyme system.

• Not all enzymes have optimum temperatures of 40 degree Celcius. Bacteria and algae living in hot springs such as this one in Yellowstone National Park, USA, are able to tolerate very high temperatures. Enzymes from such organisms are proving useful in various industrial applications.

INHIBITORS• An inhibitor is a substance that slows down the rate at which an enzyme works.

INHIBITORS

Inhibitor binds to active site on enzyme

Inhibitor binds elsewhere on enzyme

Inhibitor binds briefly Competitive reversible Non-competitive reversible

Inhibitor binds permanently Non-competitive Irreversible Non-competitive irreversible

CONCLUSION• Enzymes are globular proteins, which act as catalysts by lowering activation energy.

• Each enzyme acts on only one specific substrate, because there has to be a perfect match between the shape of the substrate and the shape of the enzyme’s active site to from an enzyme-substrate complex.

• Anything which affects the shape of the active site, such as high temperature, a change in pH or the binding of a non-competitive inhibitor with the enzyme, will slow down the rate of the reaction.

• Competitive inhibitors also slow down the rate of reaction, by competing with the substrate for the active site of the enzyme.

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