Enzymes and Cell Metabolism

• The topic is enzymes and cell metabolism.

Enzymes

• Enzymes are biological catalysts that speed up reactions without being used up in the process.
• Enzymes are composed of amino acids, forming globular, folded proteins with a 3D shape.
• Enzymes are proteins produced by ribosomes.

Substrate and Product

• The substrate is the substance with which an enzyme reacts.
• The product is the result of the reaction between an enzyme and its substrate.

Specific Enzyme Examples

• Amylase acts on starch (a polysaccharide) to produce maltose.
• Catalase acts on hydrogen peroxide to produce oxygen and water.
• Pepsin acts on protein to produce amino acids (peptides).
• Lipase acts on fats/lipids to produce glycerol and fatty acids.

Metabolism

• Metabolism is the sum of all chemical reactions in an organism.
• Catabolism is the breakdown of large molecules to release energy, such as in respiration and digestion.
• Anabolism is the conversion of small molecules into larger molecules and requires energy, such as in protein synthesis and photosynthesis.
• Enzymes control the rate of metabolic reactions.
• Pepsin, amylase, lipase, and catalase are catabolic enzymes.
• Polymerase enzymes are anabolic enzymes.

Active Site and Specificity

• The active site is the region of an enzyme that combines with the substrate.
• Specificity means an enzyme reacts with only one particular substrate.
• Denaturation occurs when the shape of an enzyme is permanently destroyed, preventing it from functioning.
• The active site is destroyed when an enzyme denatures.
• Denaturation can occur if an enzyme is heated above 40°C.

Optimum Conditions

• Optimum temperature is the temperature at which an enzyme works most effectively.
• At low temperatures, enzymes are inactive because the enzyme and substrate do not move enough to collide and form enzyme-substrate complexes.
• As temperature increases, more movement leads to more collisions and more enzyme-substrate (ES) complexes forming.
• At very high temperatures, the active site is destroyed, and the enzyme denatures.
• Optimum pH is the pH at which an enzyme functions best and extremes of pH can denature enzymes.
• Optimum enzyme activity refers to an enzyme working at its maximum rate.

Induced Fit Model

• The induced fit model of enzyme action states the substrate fits into the active site of the enzyme.
• The active site/enzyme changes shape slightly to fit precisely around the substrate.
• An enzyme-substrate complex forms, and then the product emerges.
• The enzyme returns to its original shape and can be reused.
• Factors such as temperature, pH, substrate concentration, and enzyme concentration affect enzyme activity.

Bioprocessing and Immobilized Enzymes

• Bioprocessing uses enzyme-controlled reactions to produce useful products or reactions.
• A bioreactor is the vessel in which bioprocessing takes place.
• Examples include cheese production using rennin and fructose production from glucose using glucose isomerase.
• Immobilized enzymes are enzymes trapped in a gel or fixed to an inert substance.
• Methods of enzyme immobilization include adsorption, covalent bonding, entrapment, and encapsulation.
• Advantages include the enzyme can be recovered, the enzyme can be reused and a pure sample of product is obtained.
• Lactase can be used to produce lactose-free milk by breaking down lactose into glucose and galactose.
• Glucose isomerase can be used to produce fructose from glucose.

Enzyme Experiments: Catalase and Heat Denaturation

• Catalase extracted from celery is used as the enzyme in this experiment.
• Hydrogen peroxide acts as the substrate.
• The products are water and oxygen.
• The rate of reaction is the volume of foam formed per minute.
• Factors kept constant include: temperature at 25°C, the same volume of celery extract, 6% hydrogen peroxide solution, and a buffer pH of 9.
• One factor changed is using boiled and unboiled celery extract.
• The boiled celery extract results in no foam formed.
• The unboiled celery extract results in the formation of foam.
• Boiling the celery extract denatures the enzyme, destroying its active site, hence foam no longer forms..

Enzyme Experiments: Catalase and pH

• The enzyme is Catalase and extracted from celery.
• The substrate is hydrogen peroxide.
• The products are water and oxygen.
• The rate of reaction is measured by volume of foam formed per minute.
• The factor is pH which is varied using different pH buffers.
• Factors kept constant include: temperature at 25°C, the same volume of celery extract and the same volume of 6% hydrogen peroxide solution.
• Measuring the volume of foam produced after 1 minute enables a comparison of reaction rates at different pH levels.
• The optimum pH of catalase is approximately 9, with activity decreasing at lower pH. At very low and very high pH's the enzyme is denatured and does not function.

Enzyme Experiments: Enzyme immobilization

• Sucrase is the enzyme.
• Sucrose is the substrate.
• Glucose and fructose are the product.
• Yeast is the source of the enzyme.
• Sodium alginate is used to immobilize or trap the enzyme.
• Calcium chloride is used to harden the beads of alginate.
• Sucrose is broken down into glucose and fructose by the action of the enzyme sucrase.
• The presence of glucose is tested, using glucose listing strips which change color when glucose is present.
• Turbidity (cloudiness) of each solution is measured.