Topic 2.5 Enzymes

IB BiologyS. Dosman

Topic 2.5 Outcomes

2.5 (U1) Enzymes have an active site to which specific substrates bind.2.5 (U2) Enzymes catalysis involves molecular motion and the collision of substrates with the active site.2.5 (U3) Temperature, pH and substrate concentration affect the rate of activity of enzymes.2.5 (U4) Enzymes can be denatured.2.5 (U5) Immobilized enzymes are widely used in industry.

Enzyme

• Enzymes are catalysts that are produced by living organisms and are therefore often referred to as biological catalysts.

• A catalyst speeds up chemical reactions without being changed by the reaction itself.

• Enzymes are globular proteins which act as catalysts in chemical reactions in organisms.

Substrate

• A substrate is a substance or material that an enzyme acts upon.

• An enzyme may act upon one substrate to break it into two products or it may act upon two substrates to create one product.

• Catabolic metabolism breaks one substrate into two products.

• Anabolic metabolism creates one product from two substrates.

Active site• Enzymes are composed of

long chains of amino acids that have folded into a very specific three-dimensional shape which contains an active site.

• An active site is a region on the surface of an enzyme to which substrates will bind and which catalyses a chemical reaction involving the substrate.

Enzyme-Substrate Specificity

• The active site of each enzyme has a very specific and intricate shape and it also has distinct chemical properties that match those of its substrate. Not only does the substrate molecule fit the shape of the active site but it is also chemically attracted to it.

• This is known as enzyme-substrate specificity. The enzyme and substrate fit together like a key fits a specific lock. The enzyme is the lock and the substrate is the key.

Denaturation

• In proteins, a process in which a protein unravels and loses its native conformation, thereby becoming biologically inactive.

• In DNA, the separation of the two strands of the double helix.

• Denaturation occurs under extreme conditions of pH, salt concentration, and temperature.

Catalyst

• A chemical agent that changes the rate of a reaction without being consumed by the reaction.

Immobilized Enzymes

• Enzymes used in industry that attach to another material in such a way that the movement of the enzyme is restricted.

1. Explain how a substrate bonds to the active site of an enzyme. Make sure your answer includes an explanation of the role of enzyme-substrate specificity.

• There are thousands of biochemical reactions that take place and each one requires a specific enzyme for each substrate.

• The shape and chemical properties of the enzyme match that of the substrate. The substrate binds to the active site of the enzyme, it is converted into products and then released by the enzyme. The enzyme is now free to catalyze another substrate.

2. Describe the three stages that occur when an enzyme catalysis a reaction.

• Stage 1: the substrate binds to the active site of the enzyme. There are some enzymes that have different parts to their active site and can bind two substrates.

• Stage 2: the substrates change into different chemical substances (products) while they are still bound to the active site.

• Stage 3: The active site releases the products and it is now free to catalzye another substrate.

3. Explain the role of molecular motion and collisions between substrates and enzymes during catalysis.

• In most reactions the substrates are dissolved in water and the particles are in constant, random motion. These substrate particles will collide with the enzymes due to this random motion and if the angle is correct, the substrate can bind with the active site on the enzyme.

• The substrate molecules are smaller than the enzyme and moving faster as well. This random motion is responsible for the collisions and eventual catalyst of the substrate.

What can affect enzyme activity?

• Enzymes can be affected by three different factors in their environment.

• A change in these factors can affect the rate at which the enzyme will work or they can render it ineffective. Enzymes must have the right conditions they need in order to work effectively.

• Enzyme activity is affected by temperature, pH, and the concentration of the substrate.

#4. Enzymes and Temperature• Enzyme activity will increase

as temperature increases (often doubles with every 10˚C rise). At a higher temperature more collisions occur between the substrate and the enzymes due to faster movement of molecules.

• However, at high temperatures enzymes are denatured and stop working. High heat causes vibrations inside the enzymes which break bonds needed to maintain the structure of the enzyme.

#5. Enzymes and pH

• As pH levels increase or decrease from the optimum level for each specific enzyme, the activity level is reduced.

• Both acids and alkalis can denature enzymes. A pH of 7 is optimum for most enzymes.

#6. Enzymes and concentration of substrate

• Enzyme activity is directly proportional to substrate concentration at low concentration levels. As the concentration of the substrate rises, the enzyme activity increases because random collisions of substrate molecules and enzymes increases as the concentration of the substrate increases.

• At high substrate concentrations, all the active sites of the enzymes will be occupied so raising the concentration level will no longer have an effect.

7. Describe how enzymes can be denatured.

• Denaturation is changing the structure of an enzyme (protein) that results in the loss (usually permanent) of its biological properties. This means it can no longer carry out its function because the active site is altered in such a way that the substrate can no longer bind.

• Denaturation occurs as a result of a change in temperature or pH.

8. Explain how immobilized enzymes are used in industry and what advantages there are to using them.

• Enzymes can be used outside of living things as catalysts and have many uses in industry. Humans now make commercial use of more than 500 enzymes in industries such as biotechnology, energy, environment, food & nutrition, agriculture, medical uses and others.

• The enzymes used are immobilized and have several advantages.

Advantages of Immobilized Enzymes

• Separation of enzyme from product occurs easily so the reaction stops at the right time and prevents contamination of the product.

• Once extracted from the mixture the enzymes may be used again making them cost effective.

• Immobilized enzymes are more stable and therefore more resistant to changes in pH and temperature. This means a lower rate of denaturation and replacement.

• The enzyme concentration can be higher than with dissolved enzymes which increases the rate of reaction.

Uses of enzymes in industrial processes

• Enzymes are used in many biological processes (biotechnology).

• These advances can have many benefits for the human population.

• Some examples are the use of enzymes in laundry detergent, preparation of textiles for clothing, tanning hides into leather, biodegradable plastics and the biofuel bioethanol.

2.5 A1 – Methods of production of lactose-free milk and its advantages.

• Enzymes are a very important part of biotechnology, which is the use of organisms or parts of organisms to produce things or carry out useful processes.

• Lactose is a dissacharide found in milk. The enzyme lactase is used to break it down into glucose and galactose (two monosaccharides). Under normal circumstances the human body produces enough lactase to break down any lactose consumed in the diet.

The use of lactase in the production of lactose-free milk.

• Biotechnology companies culture a particular species of yeast known as Kluveromyces lactis which grows naturally in milk. These yeast produce lactase which the companies extract and purify to sell to food manufacturing companies.

• Lactase can be added to milk to break down lactose into glucose and galactose. This is very helpful to people who are lactose intolerant. People who are lactose intolerant do not produce enough lactase to break down the lactose found in milk and milk products. By adding lactase to milk, the lactose is broken down before it is consumed therefore making the milk product lactose-reduced and it can be consumed by an individual with lactose intolerance.