Enzymes and Metabolic Processes

Enzyme and Metabolism

Metabolism

• Metabolism is the sum of all the chemical reactions that take place in an organism.
• Metabolism is divided into two main processes: catabolism and anabolism.

Catabolism

• Catabolism is the breakdown of complex molecules into simpler ones.
• Catabolic reactions release energy.
• An example of catabolism is respiration, where glucose is broken down into water and carbon dioxide, releasing energy.

Anabolism

• Anabolism is the building up of simple molecules into complex ones.
• Anabolic reactions require energy.
• An example of anabolism is the condensation of glucose molecules to form starch.

Common Usage of Terms

• Catabolism and anabolism can refer to a chain reaction or a series of reactions.

Metabolic Rate

• Metabolic rate is the overall speed of the chemical reactions in an organism.
• Several factors affect metabolic rate.

Energy and Chemical Reactions

• Chemical reactions need energy to occur
• Chemical reactions need energy to overcome the energy barrier.
• Supplying energy helps the process.
• Increasing the temperature is not always possible due to harm to body cells.

Enzymes

• Enzymes speed up chemical reactions by lowering the energy barrier.
• Enzymes are proteins that act as biological catalysts.
• The formation of an enzyme-substrate complex creates an alternative pathway that lowers activation energy, which allows chemical reactions to occur in living cells and accelerate the reaction rate.
• Metabolic reactions would proceed very slowly, or even stop, without enzymes.
• Enzymes function as biological catalysts that decrease activation energy to speed up chemical reactions.

Active Site

• Each enzyme has an active site with a specific shape.
• An active site can combine with substrate molecules because shapes fit together.
• An enzyme-substrate complex provides an alternative reaction with lower activation energy to speed up living cell reaction rate.
• The active site combines with substrate molecules and then breaks down to give products.
• In catabolic reactions, the enzyme helps to break the substrates apart.
• In anabolic reactions, the enzyme helps to join the substrates together.
• Once the enzyme substrate complex is formed, it breaks down to yield the product and releases the enzyme in its original form.
• Enzymes act as biological catalysts.

Properties of Enzymes

Lock and Key Hypothesis

• Enzymes are proteins, which act as biological catalysts.
• Each enzyme has an active site of a specific shape.
• The lock-and-key hypothesis explains the specificity of enzyme action.
• Enzymes combine with a particular substrate.
• Enzymes are specific in action and they can only fit specific substrate(s) to form enzyme-substrate complex
• Once an enzyme finishes a reaction, it will be released with an intact active site, so the enzyme is reusable.

Enzyme Characteristics

• Enzymes are reusable and return to their original form after reaction.
• Enzymes are required in small amounts but produce large amounts of products.
• Enzymes are specific.
• Each enzyme combines with a specific substrate and catalyses only one type of reaction.
• Enzyme action can be explained by the lock-and-key hypothesis.

Biological Catalysts

• Enzymes act as catalysts in organisms.
• Enzymes speed up metabolic reactions.
• Enzymes are denatured at high temperatures and extreme pH levels.
• Enzymes work best under optimum temperature and pH value.

Measuring Enzymatic Rates

• Enzymatic rates can be measured by the rate of substrates being used up or by the rate of product formation.

Factors Affecting Enzyme Activity: Temperature

• At low temperatures, enzymes have low kinetic energy and therefore move slowly.
• Enzymes moving slowly leads to less chance of collision so reactions are slower.
• At high temperatures, enzymes have more kinetic energy and therefore move more rapidly.
• Enzymes with higher kinetic energy collide more frequently and cause higher enzyme activity.
• At optimum temperatures enzyme activity is at its peak.
• When the temperature gets too high, the conformation of the active site begins to change and enzymes are denatured.
• Denatured enzymes mean substrates no longer fit, and enzyme activity permanently decreases.

Factors Affecting Enzyme Activity: pH

• Different enzymes have different optimum pH levels. For example:
• Pepsin has an optimum pH of 2.
• Salivary amylase has an optimum pH of 7.
• Pancreatic lipase has an optimum pH of 9.
• An unsuitable pH can lead to conformational changes to the active sites, denaturing the enzyme.
• Denatured enzymes means substrates no longer fit, and enzyme activity permanently decreases.

Factors affecting enzyme reactions: Enzyme Concentration

• With excess substrate available, higher enzyme concentrations lead to more active sites for substrates to collide and form an enzyme-substrate complex.

Factors affecting enzyme reactions: Substrate Concentration

• With sufficient enzyme available, higher substrate concentrations increase the chance to form an enzyme-substrate complex once the enzyme is not occupied.
• At the saturation point, all active sites of the enzyme molecules are occupied by substrates, and the reaction rate plateaus.

Inhibitors

• Inhibitors are substances that decrease enzyme activity, such as cyanides and some heavy metals.

Competitive Inhibitors

• Having a similar shape to the real substrate, competitive inhibitors reversibly bind with the active sites of the enzymes.
• The inhibitory effect can be overcome by increasing substrate concentration.

Non-competitive Inhibitors

• Non-competitive inhibitors bind to the allosteric sites of enzymes, which are sites other than active sites.
• Binding denatures the enzymes by changing the shape of the active site of the enzymes, either irreversibly or reversibly.
• The substrate cannot bind to the active sites, so the inhibitory effect cannot be overcome by increasing substrate concentration.

Enzyme Applications

• Enzymes can originate from plants, animals, or microorganisms, and are extracted and used in:
• Food Processing.
• Biofuels.
• Clothing.
• Medical.
• Personal care.

Enzyme Applications: Food Processing

• Fruit Juice Extraction: Pectinases catalyse the breakdown of cell walls within fruit to release juice inside, maximising the yield of fruit juice extraction - pectinases also clarify the juices.
• Baby food: Proteases pre-digest some of the proteins for easier digestion and absorption by babies.
• Syrups: Amylase catalyses the breakdown of corn starch into sugars.
• Meat tenderisers: Proteases digest proteins in meat, which soften the meat before cooking.

Enzyme Applications: Clothing Industry

• Stonewashed Jeans: Use of enzymes replaces washing jeans with stones to break cellulose fibres. Jeans become less stiff, production cost decreases, and the amount of removed dye is controlled.

Enzyme Applications: Medical

• Glucose Test Strips: Enzymes in test strips catalyses oxidation of glucose to detect the sign of diabetes.
• Enzyme Injections: Enzyme injections help dissolve blood clots if patients suffer from excessive blood clotting that block blood flow and lead to heart attack or stroke
• Lysozyme: Lysozyme is used in anti-inflammatory drugs, and naturally weaken bacterial cells to kill them allowing them to rupture.

Enzyme Applications: Personal Care

• Contact Lens Cleaners: Proteases remove protein deposits from contact lenses to relieve discomfort and prevent blurred vision, and increased risk of eye problems.
• Biological Washing Powde: Lipases, amylases, and proteases breakdown substances in food stains on clothes.

Enzyme Applications: Biofuels

• Fuels are produced from plant materials such as maize and enzymes break down starch in crops into sugars to produce ethanol as fuel for vehicles

Advantages of Using Enzymes

• Enzymes speed up chemical reactions.
• They mass-produce more quickly, with a higher product yield.
• Enzymes are specific in action.
• They only catalyse specific processes, while giving specific products and reduces the potential for the generation of undesirable products.
• Enzymes are reusable in small amounts.
• Enabling users the ability to convert a lot of substrates into useful products.
• Enzymes permit reactions to manifest in mild conditions without high temperatures or extreme pHs.
• This helps to reduce production costs.
• Enzyme activity can be easily regulated by adjusting reaction temperature or pH.
• Enzymes are non-toxic and biodegradable and replace harmful chemicals to produce fewer pollutants.