Enzymes and Their Functions

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Questions and Answers

What role does isoleucine play in the enzyme threonine deaminase?

It degrades threonine into isoleucine.

It acts as an allosteric inhibitor at a site outside the active site. (correct)

It directly activates threonine deaminase.

It acts as a competitive inhibitor at the active site.

What happens to threonine deaminase when isoleucine binds to it?

It increases its affinity for threonine.

The enzyme is inhibited and converted to the T state. (correct)

Threonine deaminase is converted to the R state.

It enhances the production of isoleucine.

Which of the following correctly describes cofactors?

They are never involved in electron transport.

Cofactors are always organic molecules.

Cofactors enhance the substrate's stability.

They are required by some enzymes to bind substrates. (correct)

How do coenzymes assist enzymes in biochemical reactions?

They shuttle molecules from one enzyme to another. Signup and view all the answers

What will occur if the concentration of isoleucine decreases in a cell?

Threonine deaminase will regain its ability to function and produce isoleucine. Signup and view all the answers

What role do enzymes play in chemical reactions?

They speed up reactions by lowering activation energy. Signup and view all the answers

What is the significance of the active site in enzyme function?

It is the area where substrate binding occurs. Signup and view all the answers

How do enzymes lower the activation energy of a chemical reaction?

By forming enzyme-substrate complexes. Signup and view all the answers

Which of the following correctly describes the induced-fit model?

The enzyme changes shape slightly to better accommodate the substrate. Signup and view all the answers

What happens to enzyme activity as temperature increases?

Activity initially increases until reaching an optimal temperature. Signup and view all the answers

What is the correct function of a hydrolase enzyme?

Breaks down starch by hydrolysis. Signup and view all the answers

Which statement describes the lock and key model for enzymes?

The substrate must have a complementary shape to the active site. Signup and view all the answers

In what type of reaction do enzymes facilitate the formation of bonds between substrates?

Anabolic reactions only. Signup and view all the answers

What is the optimal temperature for enzyme activity in humans?

37oC Signup and view all the answers

How does pH affect enzyme activity?

Enzymes have an optimal pH range for maximum activity. Signup and view all the answers

What occurs when substrate concentration increases beyond a certain point?

All active sites of the enzymes are occupied. Signup and view all the answers

What distinguishes a competitive inhibitor from a non-competitive inhibitor?

Competitive inhibitors bind to the active site. Signup and view all the answers

What is the function of allosteric activators?

They stabilize the enzyme's active shape. Signup and view all the answers

What is feedback inhibition?

It involves a product from a later step inhibiting an earlier enzyme. Signup and view all the answers

Which of the following statements correctly describes enzyme denaturation?

It occurs when enzymes are exposed to extreme pH or temperature. Signup and view all the answers

Which of the following factors does NOT affect enzyme activity?

Color of the enzyme Signup and view all the answers

Study Notes

Enzymes

Enzymes are protein catalysts that speed up chemical reactions by lowering activation energy.
Enzymes are not used up during a reaction.
Enzymes are specific to a particular substrate (reactant).
Enzymes function by lowering the activation energy needed to break bonds between reactant molecules.
Enzymes can add or remove protons.
Enzymes can twist or bend molecules.
Enzymes can increase the probability of molecules coming in close proximity and reacting.

Enzyme Nomenclature

Enzymes are named for the molecule acted upon with the suffix "-ase" (hydrolytic enzymes).
For example, amylase breaks down starch, lactase catalyzes lactose, and peptidase breaks peptide bonds.
Many enzymes also end with "in" e.g. trypsin, pepsin.

Lock and Key Model

Enzymes are specialized for a particular type of reaction.
The substrate and the active site must possess complementary shapes for binding to occur.

Induced-Fit Model

Enzymes can slightly change their shape to better accommodate the substrate.
This is known as induced fit.

How Enzymes Lower Activation Energy

Enzymes form enzyme-substrate complexes.
Substrates bind to the active site on the enzyme.
The active site undergoes a slight conformation change (induced fit) to better accommodate the substrate.

Enzyme-Substrate Complex and Activation Energy

In catabolic reactions, the interactions between the substrate and enzyme cause stress or distortion of the bonds in the substrate, allowing them to break.
In anabolic reactions, the enzyme allows two substrates to have the proper orientation for bonds to form between them.

Factors Affecting Enzyme Activity

Temperature:
- As temperature rises, reacting molecules gain more kinetic energy which increases the chances of successful collisions.
- This increases the rate of the reaction.
- Enzymes have an optimal temperature for their activity. In humans, the optimal temperature is 37°C.
- At temperatures higher than optimal, enzymes denature.
pH:
- Enzymes work within a very small pH range.
- Optimal pH is the level where an enzyme performs at its greatest activity.
- pH levels outside of the optimal range can cause denaturation.
Concentration of substrate and enzyme:
- The rate of reaction increases with an increase in either the substrate or enzyme concentration.
- Eventually, all of the active sites of the enzymes become occupied and the reaction reaches saturation.
- To continue the reaction, an enzyme-substrate complex must dissociate to free up an active site.
Inhibition:
- Competitive Inhibitors:
  - Similar to the enzyme's substrate and can bind to the active site, blocking the normal substrate.
- Non-competitive Inhibitors:
  - Bind to the enzyme at an allosteric site (not the active site) and cause a conformational change, preventing the normal substrate from binding.
Allosteric Regulation:
- Cells control enzyme activity to coordinate cellular activities.
- Activators can bind to allosterically controlled enzymes to stabilize its shape, keeping all active sites available.
- Allosteric inhibitors can bind to allosterically controlled enzymes to stabilize the inactive form of the enzyme.
Feedback Inhibition:
- This method is used by cells to control metabolic pathways involving a series of reactions.
- A product formed later in the sequence allosterically inhibits an enzyme that catalyzes a reaction earlier in the pathway.
- Feedback inhibition prevents too much buildup of product.
Cofactors and Coenzymes:
- Required by some enzymes to function.
- Bind to the active sites of enzymes.
- Cofactors are inorganic, non-protein components. They usually attract electrons in the substrate to assist in breaking bonds (e.g. Zn²⁺ and Mn²⁺).
- Coenzymes are organic, non-protein molecules, such as the derivatives of many vitamins. They often shuttle molecules from one enzyme to another (e.g. vitamin B₃ is a coenzyme of NAD⁺).

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Description

This quiz covers the essential concepts of enzymes, including their role as protein catalysts, their specific naming conventions, and the models explaining their interactions with substrates. Test your knowledge on enzyme functionality and nomenclature.