Enzymes

Enzymes

-Catalysts that speed up the rate of a chemical reaction without being changed or used up in the reaction -Proteins -Biological catalysts (biological because they are made in living cells, catalysts because they speed up the rate of chemical reactions without being changed) -Necessary to all living organisms as they maintain reaction speeds of all metabolic reactions (all the reactions that keep an organism alive) at a rate that can sustain life. =For example, if we did not produce digestive enzymes, it would take around 2 - 3 weeks to digest one meal; with enzymes, it takes around 4 hours

Effect of temperature on enzymes

Enzymes are proteins and have a specific shape, held in place by bonds. This is extremely important around the active site area as the specific shape is what ensures the substrate will fit into the active site and enable the reaction to proceed. Enzymes work fastest at their 'optimum temperature' - in the human body, the optimum temperature is 37⁰C. Heating to high temperatures (beyond the optimum) will break the bonds that hold the enzyme together and it will lose its shape -this is known as denaturation. Substrates cannot fit into denatured enzymes as the shape of their active site has been lost. Denaturation is irreversible - once enzymes are denatured they cannot regain their proper shape and activity will stop. Increasing the temperature from 0⁰C to the optimum increases the activity of enzymes as the more energy the molecules have the faster they move and the number of collisions with the substrate molecules increases, leading to a faster rate of reaction. This means that low temperatures do not denature enzymes, they just make them work more slowly.

How do enzymes work?

Enzymes are specific to one particular substrate (molecule/s that get broken down or joined together in the reaction) as the enzyme is a complementary shape to the substrate The product is made from the substrate(s) and is released

Enzyme action and specificity

Enzymes are specific to one particular substrate(s) as the active site of the enzyme, where the substrate attaches, is a complementary shape to the substrate. This is because the enzyme is a protein and has a specific 3-D shape. This is known as the lock and key hypothesis. When the substrate moves into the enzyme's active site they become known as the enzyme-substrate complex. After the reaction has occurred, the products leave the enzyme's active site as they no longer fit it and it is free to take up another substrate. 1. Enzymes and substrates randomly move about in solution 2. When an enzyme and its complementary substrate randomly collide - with the substrate fitting into the active site of the enzyme - an enzyme-substrate complex forms, and the reaction occurs. 3. A product (or products) forms from the substrate(s) which are then released from the active site. The enzyme is unchanged and will go on to catalyse further reactions.

Effect of pH on enzymes

The optimum pH for most enzymes is 7 but some that are produced in acidic conditions, such as the stomach, have a lower optimum pH (pH 2) and some that are produced in alkaline conditions, such as the duodenum, have a higher optimum pH (pH 8 or 9). If the pH is too high or too low, the bonds that hold the amino acid chain together to make up the protein can be destroyed. This will change the shape of the active site, so the substrate can no longer fit into it, reducing the rate of activity. Moving too far away from the optimum pH will cause the enzyme to denature and activity will stop.