Maintaining a Balance

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Maintaining a Balance

1. Most organism are active in a limited temperature range

The role of Enzymes in metabolism, their chemical composition and specificity on substrates

Role of enzymes
* Enzymes are organic catalysts. They are protein molecules that increase the rate of the reactions in living organisms. * Without enzymes, metabolic reactions at body temperatures would be too slow to produce sufficient energy to maintain life * Intracellular enzymes are used in the cells that produce them e.g cellular respiration or photosynthesis * Extracellular enzymes act outside producer cells e.g. digestive enzymes.

Chemical composition
* Enzymes are proteins made of amino acids linked and folded to produce a 3D structure specific to a certain substrate * Composed of carbon, hydrogen, oxygen and nitrogen
* Each enzyme catalyses a distinct chemical reaction in which it combines with the substrate to form an enzyme substrate molecule upon which the substrate is broken down * One model used to illustrate the action of an enzyme is the lock-key model. This is where only one small part of the enzyme molecule can form a complex with the substrate. This part of the molecule is called the active site. Only a specific substrate can bond in that site and this makes the enzyme specific to that substrate. * The induced fit model, a more recent modification on the lock-key model, proposes that the active site slightly changes its shape to accommodate the substrate perfectly.

Factors affecting enzyme activity
* Temperature
* Increased temperature causes increased reaction rate as molecules move more rapidly and collide more with the enzymes active site * If temperature is too high, the enzyme denatures and can no longer bind with substrate * Substrate concentration

* The higher the substrate concentration the higher chance of collision with the enzyme active site * pH
* each enzyme is specific to a location in the body with a certain pH. If pH is less than or greater than the optimal range, the enzyme denatures * Presence of coenzymes or co-factors
* Presence of enzyme inhibitors
* Other molecules may compete with the normal substrate for the active site of enzyme, interfering with the normal substrate-enzyme reaction First Hand investigations
Effect of increased temperature on enzyme activity
Aim: to investigate the effect of temperature on activity of enzyme rennin Method: 1. set up five experimental groups of test tubes ads below 2. Maintain temperatures by using a water bath for each group Group 1 – 0C| Group 2 – 20C| Group 3 – 38C| Group 4 – 80C| Group 5 – 100C| A| B| A| B| A| B| A| B| A| B|

10 ml milk| 10 mil milk + ½ crushed junket tablet| 10 ml milk| 10 mil milk + ½ crushed junket tablet| 10 ml milk| 10 mil milk + ½ crushed junket tablet| 10 ml milk| 10 mil milk + ½ crushed junket tablet| 10 ml milk| 10 mil milk + ½ crushed junket tablet| 3. Record time taken for milk to coagulate in each test tube Test Tube| Coagulation time|

Group 1| A| No change|
| B| No change|
Group 2| A| No change|
| B| No change|
Group 3| A| No change|
| B| 7.1 minutes|
Group 4| A| No change|
| B| Instant coagulation|
Group 5| A| No change|
| B| No change|
Independent variable: temperature
Dependent variable: time taken to coagulate
Controlled variables: amount of milk, amount of junket, lack of stirring, test tube surface area, type of milk

Effect of pH on enzyme activity
Aim: to test the relative activity of the enzyme pepsin under different conditions of pH Method:
1. Dissolve ½ teaspoon of pepsin in 100ml distilled water. Add different amounts of acid and water to prepare seven pepsin solutions with a pH from 2 – 8

2. Set up 4 test tubes as below

1| 2| 3| 4|
10ml pepsin solution pH 2| 10ml pepsin solution pH 4| 10ml pepsin solution pH 6.8| 10ml...
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