Biochemistry Chapter 4: Enzymes

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Questions and Answers

What is the primary role of an enzyme in a chemical reaction?

To lower the activation energy required for the reaction (correct)

To change the concentration of reactants

To alter the products formed in the reaction

To increase the temperature of the reaction

In the lock and key model, what is true about the substrate?

It can fit any enzyme regardless of shape

It is complementary to the enzyme's active site (correct)

It changes shape to fit the enzyme during the reaction

It is released from the enzyme without any modification

What happens to the free energy change (ΔG) of a reaction when an enzyme is present?

ΔG decreases significantly

ΔG becomes negative

ΔG remains unaffected (correct)

ΔG increases significantly

Which statement about product formation in enzyme reactions is correct?

The product has a different shape from the substrate Signup and view all the answers

What is one consequence of enzyme inhibitors?

They block the binding site for the substrate Signup and view all the answers

Which term is used to describe the combination of an enzyme and its substrate?

Enzyme-substrate complex Signup and view all the answers

What aspect of the enzyme's structure is crucial for its specificity?

The shape of the active site Signup and view all the answers

Why is the lock and key model considered incorrect?

It does not account for the flexibility of the enzyme Signup and view all the answers

Which class of enzymes catalyzes the transfer of a functional group from one substrate to another?

Transferase Signup and view all the answers

What is a potential disadvantage of using immobilized enzymes in industrial processes?

Possible partial loss of enzyme activity Signup and view all the answers

Which reaction is catalyzed by the enzyme Dipeptidase?

Hydrolysis reaction Signup and view all the answers

Which method of enzyme immobilization allows an enzyme to be trapped within a three-dimensional structure?

Entrapment Signup and view all the answers

What is the role of ligases in enzymatic reactions?

Catalyze bond formation using energy from ATP Signup and view all the answers

Which of the following is NOT a common method of enzyme immobilization?

Saturation Signup and view all the answers

Which of the following is a characteristic of isomerases?

They rearrange atoms within a molecule Signup and view all the answers

What is the major benefit of using immobilized enzymes in industrial processes?

Minimized product contamination Signup and view all the answers

What triggers feedback inhibition in the synthesis of isoleucine?

An accumulation of isoleucine Signup and view all the answers

What is the role of threonine deaminase in the isoleucine synthesis pathway?

Catalyzes the first step of isoleucine synthesis Signup and view all the answers

How do the classifications of enzymes help in understanding their function?

By grouping them based on the type of reaction they catalyze Signup and view all the answers

What would most likely happen if a cell accumulates too much isoleucine?

Inhibition of threonine deaminase activity Signup and view all the answers

Which of the following classes of enzymes is involved in oxidation-reduction reactions?

Oxidoreductases Signup and view all the answers

Study Notes

Chapter 4: Enzymes

Enzymes are organic catalysts, typically proteins
They accelerate specific chemical reactions by lowering the activation energy (Ea)
Enzymes are globular proteins
Enzymes are not permanently changed/consumed by the reaction
Enzymes can be reused
Enzymes have one or more active sites where substrates bind
Enzymes lower activation energy (Ea) needed for a reaction to start

4.1 Catalysis and Concept of Activation Energy

Activation energy (Ea) is the initial energy needed to start a chemical reaction
The source of Ea is heat energy from the surroundings
Enzymes lower Ea by:
- Bringing substrates together with correct orientation
- Providing a favorable cellular microenvironment
- Stretching substrate bonds toward their transition state
- Forming temporary covalent bonds with substrate

4.2 Mechanism of Enzyme Action: Lock and Key Model

The substrate is complementary to the active site of the enzyme
Substrate binds to the active site of the enzyme
Enzyme-substrate complex formed
Old bonds break and new ones form
Substrates change to product
Product has a different shape from the substrate
Product is released from the enzyme

4.2 Mechanism of Enzyme Action: Induced-Fit Model

Substrate not perfectly complementary to active site
Binding of substrate induces a slight conformational change in the enzyme's active site
Shape of substrate also changes slightly
Catalytic groups on enzyme are correctly oriented with the substrate
Old bonds break, and new bonds form
Substrate is changed into a product
Product has a different shape from the substrate
Product is released from the enzyme
Enzyme returns to its original shape

4.3 Factors Affecting the Rate of Enzyme Reactions

Enzyme concentration
Temperature
pH
Substrate concentration

4.4 Enzyme Kinetics

Study of enzyme reaction rate
Enzyme-catalyzed reactions often follow a hyperbolic curve
Michaelis-Menten kinetics can explain how enzymes enhance reaction rates and how reaction rates depend on enzyme and substrate concentrations.
Michaelis-Menten kinetics model is represented by the saturation plot

4.4 Lineweaver-Burk Plot

Double-reciprocal graph of the Michaelis-Menten equation
Plots 1/v (reaction rate) against 1/[S] (substrate concentration), where 'v' is reaction rate and '[S]' is substrate concentration
Produces a straight line, useful for accurately determining Vmax (maximum reaction rate) and Km (Michaelis-Menten constant)

4.5 Cofactors

Non-protein molecules or ions needed for enzyme function
- Coenzymes: organic molecules that bind loosely and temporarily to the active site. They often carry chemical groups, atoms, or electrons between molecules
- Metal ions: inorganic ions that can activate or stabilize the enzyme's structure and function
- Prosthetic groups: tightly bound organic molecules essential for enzyme activity

4.6 Enzyme Inhibition

Inhibiting agents are chemicals that selectively reduce the function of specific enzymes.
Reversible inhibitors: bind reversibly to the enzyme, form weak bonds (like hydrogen bonds) and enzymes can return to functional structure
Irreversible inhibitors: bind irreversibly to the enzyme, strong covalent bonds forming, which inactivates the enzyme permanently

4.6 Competitive Inhibitors

Similar shape to the natural substrate
Compete with the substrate for the active site
Can be overcome by increasing substrate concentration
Reduce the rate of reaction and product formation

4.6 Non-competitive Inhibitors

No structural similarity to the natural substrate
Bind to the allosteric site
Binding causes conformational changes in the enzyme
Substrate cannot bind to the active site
Slower rate of reaction and reduced product formation

4.7 Regulation of Enzyme Activity

Cells regulate their metabolic pathways by controlling when and where enzymes are active
Mechanisms include:
- Feedback inhibition: End product inhibits an enzyme earlier in the pathway.
- Allosteric regulation: Regulatory molecules bind to a site (allosteric site) other than the active site, changing the enzyme's conformation and activity
- Cooperativity (a type of allosteric regulation): Binding of a substrate to one active site affects activity at other active sites

4.8 Enzyme Classification

Enzymes are named by adding "ase" to the name of the reaction catalyzed
Six classes: Oxidoreductases, Transferases, Hydrolases, Lyases, Isomerases, Ligases, based on the type of reaction catalyzed

4.9 Enzyme Technology

Enzymes are useful outside cellular systems for industrial and medical use
Immobilization: Enzymes are attached or trapped in insoluble materials. This helps with product yield and reusing enzymes.
- Immobilization methods: adsorption, entrapment, encapsulation, and covalent bonding
Advantages of immobilization: Stability, Reusability, Prevention of product contamination, Easier separation.
Disadvantages of immobilization: Partial loss of enzymatic activity, altered kinetics.

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Description

Explore the fascinating world of enzymes in this quiz on Chapter 4. Learn how these organic catalysts function, their role in lowering activation energy, and the mechanisms of enzyme action, including the lock and key model. Test your knowledge on key concepts from biochemistry related to enzymes.