Enzyme Functions and Properties

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Questions and Answers

What is the primary role of ligases in biochemical reactions?

They transport substrates across membranes.

They catalyze degradation reactions.

They synthesize various bonds coupled with ATP breakdown. (correct)

They inhibit enzyme activity.

Which property allows enzymes to be reused multiple times in reactions?

Their ability to form ES complexes.

Low turnover number.

High specificity for substrates.

Not being consumed in the reaction. (correct)

What factor primarily affects the rate of enzyme-catalyzed reactions according to enzyme kinetics?

Substrate specificity.

Activation energy. (correct)

Enzyme concentration.

The presence of ligands.

How do enzymes lower the activation energy of a reaction?

By changing the route of the reaction. Signup and view all the answers

What can inhibit the activity of an enzyme?

Enzyme inhibitors. Signup and view all the answers

What is the effect of increasing temperature on enzyme activity, up to a certain point?

It increases kinetic energy and the rate of reactions. Signup and view all the answers

Which of the following statements is true regarding enzyme specificity?

Each enzyme typically catalyzes one particular reaction. Signup and view all the answers

How do cofactors influence enzyme activity?

They are required for the catalytic activity of some enzymes. Signup and view all the answers

What part of the electromagnetic spectrum corresponds to visible light that the human eye can detect?

380-770 nm Signup and view all the answers

What role does color play in consumer perception of food quality?

It is a significant factor in purchasing decisions. Signup and view all the answers

Which of the following colorants is categorized as a certified dye?

FD&C Red No. 40 Signup and view all the answers

What is a potential drawback of using turmeric as a natural color in food?

It can introduce unwanted flavors to the final product. Signup and view all the answers

How does color influence flavor perception in consumers?

By associating colors with specific flavors or fruits. Signup and view all the answers

Which natural color is used specifically for pickles and soft drinks?

Anthocyanin Signup and view all the answers

Which of the following is an example of a colorant that is exempt from certification?

B-Carotene Signup and view all the answers

What is a limitation of natural food colors compared to artificial ones?

Natural food colors can cause allergic reactions. Signup and view all the answers

Why are colors important when evaluating the freshness of food?

They relate to the expected maturity and quality. Signup and view all the answers

Which of the following natural colors is derived from insects?

Carmine Signup and view all the answers

What is a major reason for the limited use of natural food colors in products?

They are significantly more expensive than synthetic colors. Signup and view all the answers

What is one way in which colors can improve the appeal of food products?

By enhancing visual presentation. Signup and view all the answers

How does color perception relate to sweetness in food products?

Certain colors are commonly associated with different sweetness levels. Signup and view all the answers

Which pigment is NOT listed as a permitted natural color in India?

Carrot Extract Signup and view all the answers

What characteristic of natural food colors can affect their stability during processing?

They are often unstable during processing and storage. Signup and view all the answers

What color is riboflavin commonly used to impart in food products?

Bright yellow Signup and view all the answers

What happens to the rate of enzyme-catalyzed reactions as temperature continues to increase beyond a certain point?

The rate of reaction decreases due to bond breakage. Signup and view all the answers

What is the optimum pH value for an enzyme?

The pH at which the enzyme shapes actively complement the substrate best. Signup and view all the answers

Which factor primarily dictates the changes in reaction rate when varying enzyme concentration?

The substrate concentration relative to the enzyme. Signup and view all the answers

Why do extreme changes in pH cause enzymes to denature?

They disrupt the ionic and hydrogen bonds crucial for enzyme structure. Signup and view all the answers

What initially occurs when temperature increases in an enzyme-catalyzed reaction?

The reaction rate increases due to enhanced kinetic energy. Signup and view all the answers

At what point can substrate concentration no longer influence the rate of reaction?

When the reaction reaches its maximum rate. Signup and view all the answers

How do small changes in pH affect enzymes compared to extreme changes?

Small changes do not affect the enzyme's structure permanently. Signup and view all the answers

What occurs to weak hydrogen and ionic bonds in enzymes when temperature rises significantly?

They begin to break, altering the active site. Signup and view all the answers

Which statement accurately describes the reactivity of sugars?

Reducing disaccharides are less reactive than hexoses. Signup and view all the answers

What is a potential undesirable effect of the Maillard reaction?

Loss of nutrition component such as lysine. Signup and view all the answers

How can thermal treatment affect the color of foods?

It can lead to the destruction of natural pigments. Signup and view all the answers

What is suggested about the mechanism of non-enzymatic browning?

It may have a two-staged mechanism with first-order and zero-order kinetics. Signup and view all the answers

Which factor does NOT influence the Maillard reaction?

Time of day Signup and view all the answers

What outcome is associated with toasting bread?

It may reduce the protein efficiency ratio by half. Signup and view all the answers

Which aspect is NOT typically evaluated in color change during non-enzymatic browning?

Rate of food spoilage. Signup and view all the answers

What effect does raising the temperature have on the Maillard reaction?

It can accelerate the Maillard reaction. Signup and view all the answers

Study Notes

Ligases

Catalyze the synthesis of various bonds, primarily C-X bonds, using energy from substrates like ATP.

Properties of Enzymes

Exhibit high specificity for their substrates, catalyzing only one particular reaction.
Remain unchanged during reactions and can be reused.
Form enzyme-substrate (ES) complexes when they react with substrates.
Require only small amounts to catalyze large quantities of substrates.
Operate quickly, having high turnover numbers, converting many substrate molecules per unit time.
Affected by changes in temperature and pH.
Many require cofactors to function.
Can be slowed down or stopped by inhibitors.

Functions of Enzymes

Degradation reactions (catabolic).
Synthesis (anabolic).
Digestion.
Protection.

Enzyme Kinetics and Reactions

Studying enzyme kinetics reveals catalytic mechanisms, metabolic roles, activity control, and potential drug or agonist inhibition.

Activation Energy (Ea)

Minimum energy needed for a chemical reaction to occur.
Enzymes act as catalysts, lowering activation energy by changing the reaction pathway.
Reduced activation energy increases the number of reactant molecules reaching sufficient energy to form products.

Factors Affecting Enzyme Activity

Temperature

Increased temperature increases kinetic energy, leading to more collisions between molecules.
Initially, this enhances reaction rate due to increased collisions between enzymes and substrates.
However, excessive heat strains bonds within enzymes, causing active site shape changes and reduced substrate complementarity.
This leads to a decrease in reaction rate as temperature rises further.

pH

H+ and OH- ions interfere with hydrogen and ionic bonds maintaining enzyme structure.
Enzymes have optimal pH values where their active site conformation best complements their substrate.
Deviation from the optimal pH reduces reaction rate.
Extreme pH changes can denature enzymes, permanently disrupting their function.

Concentration

Changing enzyme and substrate concentrations influences reaction rates.
Increasing concentration of a limiting factor boosts the reaction rate until saturation is reached.
As reactions proceed, substrate depletion lowers reaction rates.
Initial Reaction Rate represents the maximum rate achievable in experimental conditions.
Increasing substrate concentration increases the rate until a plateau is reached where it becomes nonlimiting.

Maillard Reaction

Reaction between reducing sugars and free amino acids, common during heating and storage of foods.
Produces both desirable and undesirable products:
- Desirable: Caramel aromas, golden brown colors.
- Undesirable: Food darkness, off-flavor development, loss of lysine.
Significantly reduces the nutritional value of food.
Toasting can halve the protein efficiency ratio of bread.

Browning Measurement

Measured by increased absorbance at 420 and 560 nm using reflectance colorimetry, indicating colored substance formation.

Kinetics of Nonenzymatic Browning

First-order and zero-order models are employed to evaluate browning development.
Complex kinetics involving browning and pigment degradation require multifaceted models.
First-order kinetics is suggested for pigment destruction during thermal treatment.
A two-stage model is proposed:
- Zero-order color formation.
- First-order pigment destruction.
Increased temperature accelerates browning, increasing kinetic constants associated with color formation.

Factors Controlling Maillard Reaction Products

Temperature, pH, moisture level (Aw), oxygen, metals, phosphates, sulfur dioxide, and inhibitors influence browning.
Higher temperature and pH accelerate the Maillard reaction.

Food Color

Reflects or emits different quantities of energy at wavelengths stimulating the retina, creating color perception.
Visible light encompasses wavelengths between 380-770 nm.
Color perception plays a significant role in influencing consumer purchasing decisions.
Color is associated with quality and maturity in foods (e.g., redness of meat signifies freshness).
Color influences flavor perception:
- Red drinks are expected to have strawberry or cherry flavors.
- Yellow drinks are associated with lemon.
- Green drinks are associated with lime.
Color can affect perceived sweetness.
Many food pigments are unstable during processing and storage.

Natural Colors

Pigments derived from seeds, fruits, vegetables, algae, insects, and flowers.
Examples and uses of natural colors are extensively listed in the provided text.

Permitted Natural Colors in India

The Prevention of Food Adulteration Act, 1954 and associated rules permit the use of several natural colorants.

Limitations of Natural Food Colors

Some natural colors have their flavors that can alter final product taste.
Color retention can be affected by high temperatures.
Some may cause allergic reactions.
Natural colors are generally more expensive than artificial ones.
Natural ingredient scarcity can occur.

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Description

Explore the fascinating world of enzymes, including their properties, functions, and kinetics. Understand how ligases work, the importance of enzyme-substrate complexes, and the significance of activation energy in biochemical reactions.