Enzymes - Section 6.2 (not 6.4)Assignment

What is a substrate?

A reactant molecule that binds to the active site of an enzyme

What must happen immediately before a reaction occurs with or without a catalyst?

A transition state must be reached.

energy is the energy required to destabilize existing chemical bonds and initiate a chemical reaction.

Activation

What is, in general, a barrier to the formation of products during a chemical reaction?

Activation energy is required for molecules to reach the transition state and product formation to proceed.

What causes the rate of some chemical reactions to be very slow?

Activation energy is required for molecules' bonds to be destabilized, and, therefore, products to be formed. A relatively large initial input of energy, the activation energy, is required for molecules to get close enough for the rearrangement of bonds to occur.

Where does a substrate bind on an enzyme in order for a chemical reaction to take place?

Active site

How can the functioning of an enzyme be affected by the external environment?

Altering the pH can be harmful to an enzyme when the pH is outside the normal or optimal range for that enzyme. Increasing the temperature can greatly affect the functioning of some enzymes by causing denaturation.

How is KM, a measure of the concentration of substrate needed for catalysis, related to reaction velocity?

An enzyme with a higher KM requires a higher concentration of substrate to reach a particular reaction velocity.

Which of the following statements correctly describes the relationship between affinity and KM in an enzyme-catalyzed reaction?

As the affinity of enzyme and substrate increases, the KM decreases.

Why do catalysts increase the rate of a chemical reaction?

Catalysts lower the activation energy.

What are the two important roles of ribozymes?

Catalyzing the formation of peptide bonds during polypeptide formation Processing RNA molecules from precursor to mature form

What are the small chemicals, usually inorganic ions, that temporarily attach to the surface of an enzyme and promote a chemical reaction?

Cofactors

are small chemical components, usually inorganic ions, such as Zn2+, Cu2+, and Mn2+, that temporarily attach to the surface of an enzyme and promote a chemical reaction.

Cofactors

_____ inhibitors increase the KM of a reaction but do not change the Vmax.

Competitive

How do competitive inhibitors affect the velocity and Km of an enzyme-catalyzed reaction?

Competitive inhibitors do not change the maximal velocity. Competitive inhibitors raise the substrate concentration at which the velocity is half the maximal velocity.

What is an induced fit between enzyme and substrate?

Conformational changes that cause enzyme and substrate to bind more tightly to one another

What are the key features of enzymes that allow them to act as effective catalysts?

Enzymes undergo conformational changes during an enzyme-catalyzed reaction. Enzymes lower the activation energy barrier of a chemical reaction. Enzymes exhibit high substrate specificity.

Which of the following are ways that enzymes act to increase the rate of a chemical reaction?

Lowering the activation energy Positioning the reactants very close to each other Straining the bonds in the reactants Changing the local environment of the reactants

What are the proposed roles of Mg2+ and protein in RNase P?

Mg2+ and protein function to stabilize the RNA in a catalytically active conformation.

Which of the following is an accurate description of a coenzyme?

Organic molecules that temporarily attach to an enzyme and promote a chemical reaction without being changed during the reaction

Choose the first step in an experiment designed to test the effect of substrate concentration on the rate of an enzymatic reaction.

Place 1 microgram of enzyme and increasing concentrations of substrate into four tubes.

Name environmental factors that affect proper enzyme function.

Temperature, pH and ionic conditions

Which of the following describes the relationship between substrate concentration and the rate of a chemical reaction?

The velocity increases as substrate concentration increases until it reaches a plateau.

What factors determine the direction and rate of a chemical reaction?

Thermodynamics governs the direction of a reaction but not the rate of a reaction. Catalysts influence the rate of a chemical reaction. The change in free energy will determine the direction of the reaction.

What best describes the primary role of ribozyme?

They are primarily involved in the processing of RNA molecules from precursor to mature forms.

Why are irreversible inhibitors uncommon?

They are thought to be energy inefficient because they cannot be reused.

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

When reactants are bound to enzymes, they can be strained, making it easier to achieve the transition state. Enzymes can bring reactants closer together.

The agent that speeds up the rate of a chemical reaction without being changed permanently is called

a catalyst

Catalyzed reactions occur at ______ rate compared to uncatalyzed reactions.

a faster

In order for molecules to achieve the transition state, _____ energy is necessary.

activation

When an enzyme-substrate complex undergoes conformational changes during induced fit, then

activation energy is lowered.

Enzyme-mediated chemical reactions take place when the substrate molecules bind to the _____ _____ of an enzyme.

active site

Select all of the ways that enzymes can increase the rate of a chemical reaction.

brings the reactants close to one another in the correct orientation reduces the activation energy of the reaction

Any agent that speeds up the rate of a chemical reaction without being permanently changed or consumed by it is known as a(n)

catalyst

The experiments of Sidney Altman and colleagues in the 1980s demonstrated that the RNA subunit alone can act as a(n) _____.

catalyst

Lowering the activation energy of a chemical reaction will:

change the rate of the reaction but will not change its direction

_____ are small organic molecules that temporarily attach to an enzyme and promote a chemical reaction without being changed during the reaction.

coenzyme

In a chemical reaction, an enzyme's _____ must change before it can catalyze the conversion of reactants to products.

conformation

The binding and interaction of a substrate with an enzyme causes slight _____ changes in the chemical bonds of the substrate that allow for a better induced fit between enzyme and substrate.

conformational

When enzymes and substrates bind and interact, this causes _____ changes to occur that allow for a tighter fit between enzyme and substrate.

conformational

increasing the temperature outside the optimal range for an enzyme can lead to _____ of the enzyme, altering the enzyme's structure and function.

denaturation

Affinity is the degree of attraction between a(n) _____ and a(n) _____.

enzyme; substrate

_____ are a type of catalyst found in living cells that acts to speed up chemical reactions.

enzymes

The rates of enzyme-catalyzed reactions are typically millions of times _____ than corresponding uncatalyzed reactions. Listen to the complete question

faster

An enzyme with a _____ KM requires a greater concentration of substrate to achieve a particular reaction velocity compared to an enzyme with a _____ KM

higher; lower

Altering the pH outside the optimal range for a protein can cause denaturation and can ______ the function of an enzyme.

impair

The rate of a chemical reaction that is catalyzed by an enzyme will speed up as substrate concentration _____ , but eventually reaches a(n) _____.

increases; maximum

During what step in an enzyme catalyzed reaction is the activation energy lowered?

induced fit

When conformational changes cause enzyme and substrate to bind more tightly, this is called _____ _____.

induced fit

The KM of a chemical reaction is ______ to the affinity between an enzyme and its substrate.

inversely related

Enzymes increase the rate of a chemical reaction by _____ the activation energy.

lowering

An enzyme accelerates the rate of a chemical reaction by:

lowering the activation energy

Vmax is the _____ velocity or rate of a chemical reaction.

maximum

Altman et al. proposed that the catalytic function of _____ _____ could be carried out by its RNA subunit or by its protein subunit.

ribonuclease ; P

Transfer RNA (tRNA) molecules are synthesized as large precursors which are processed with the help of ______. The tRNAs are directly involved in ______ synthesis.

ribonuclease P (RNase P); protein

A catalyst that is not made of protein is called a _______.

ribozyme

Sidney Altman and colleagues discovered _____ and revealed that RNA molecules may function as catalysts.

ribozymes

Almost all enzymes bind their substrates with a high degree of _____.

specificity

For an enzyme-catalyzed reaction, the formation of product can be viewed as occurring in two steps: (1) binding or release of _____ , and (2) formation of product.

substrate

When a reactant binds to the active site of an enzyme, this produces the enzyme- _____ complex.

substrate

Two features of enzymes that allow them to act as effective catalysts are that they can bind their _____ with high degree of specificity and can undergo _____ change.

substrate ; conformational

Ribonuclease P is involved in the processing of _____ molecules.

tRNA

Precursors of _________ are edited by RNase P and are RNA molecules that play a critical role in protein synthesis.

transfer RNA (tRNA)

Once the _____ state has been achieved, a chemical reaction can proceed and products can be formed.

transition

Enzymes are typically composed of which type of macromolecule?

Protein

Ribozymes are _____ , molecules.

RNA

What conclusions were reached from the experiments of Sidney Altman and colleagues in the 1980s?

RNA molecules can function as catalysts.

At what temperature do most human enzymes function best?

37°C

How does temperature affect the functioning of an enzyme?

Increasing the temperature outside the optimal range for an enzyme can alter the enzyme's structure and impair its function.

Which inhibitors bind to enzymes covalently?

Irreversible

Altman et al. discovered that this cofactor is essential for keeping RNA subunits in a conformation that is catalytically active:

Mg2+

True or false: Enzymes are sensitive to environmental conditions and, as a result, many enzymes function best only across a narrow range of temperature and pH.

True

True or false: Only after conformational changes cause an induced fit, can substrates be converted to products during an enzyme catalyzed reaction.

True

True or false: Straining reactants and bringing them closer together are two common ways enzymes can lower the activation energy required for a chemical reaction.

True

Many human enzymes function best at 37°C, which is:

normal body temperature

If the activation energy of a chemical reaction is lowered it will:

not change the direction of the reaction increase the rate of the reaction

What best describes the range of pH where most enzymes function best?

A narrow range

The interaction between enzyme and substrate resembles a lock and key. Which of the following accurately describes this analogy?

An enzyme is like a lock, into which the substrate must fit like a key.

The enzyme hexokinase recognizes and binds to glucose but does not bind to other similar sugars such as fructose. This is an example of what property?

Enzyme specificity

What is produced by the binding of enzyme and substrate?

Enzyme-substrate complex

What is the function of enzymes in chemical reactions?

Enzymes act as catalysts to speed up chemical reactions.

Pepsin is an enzyme found in the stomach that functions best at an acidic pH. Why?

Enzymes are sensitive to pH and function best across a narrow range of pH.

Select the reasons why changes in the pH of the fluid in which an enzyme is dissolved affect the enzyme's ability to function.

Enzymes have particular pH values at which they function best.

Why is Vmax reached during chemical reactions as the amount of substrate is increased?

Eventually Vmax is reached because all enzymes are saturated with substrate. so the rate can increase no more.

Why do most enzymes function maximally in a narrow range of temperature and pH?

Exposing enzymes to temperatures and pH outside the optimal range can change the conformation of the active site or denature the protein.

True or false: The enzyme concentration at which the reaction velocity is half its maximal value is the KM.

False

How do reversible and irreversible inhibitors differ?

Reversible inhibitors bind to enzymes noncovalently Irreversible inhibitors bind to enzymes covalently

What is the function of ribonuclease P?

Ribonuclease P is involved in the processing of tRNA molecules.

What was the major discovery made by Sidney Altman and colleagues in the 1980s?

Sidney Altman and colleagues discovered ribozymes and revealed that RNA molecules may function as catalysts.

What are prosthetic groups?

Small molecules permanently attached to the surface of an enzyme that aid in enzyme function

How do the types of ribozymes differ in the functions they perform?

Some ribozymes are involved in the processing of RNA while others are involved in protein synthesis.

_____ or reactants, are molecules that bind to an enzyme at the active site and are converted to products in chemical reactions.

Substrates

What hypothesis was proposed by Altman and colleagues regarding the catalytic function of RNase P?

The catalytic function of RNase P could be carried out by its RNA subunit or by its protein subunit.

What happens when the transition state is reached?

The chemical reaction can readily proceed. Bonds are stretched to their limit in the reactant molecules.

What is affinity?

The degree of attraction between enzyme and substrate

Which of the following are steps involved in an enzyme-catalyzed reaction?

The enzyme undergoes conformational changes to bind the substrate more closely. Substrate binds to the enzyme at the active site. Substrates are converted to products. Products are released from enzyme and enzyme is reused.

What is Vmax?

The maximal rate of a chemical reaction

What is KM?

The substrate concentration at which the reaction velocity is half its maximal value

Select the best description of product formation in enzyme-catalyzed reactions:

Two steps: binding or release of substrate and product formation

When is Vmax reached as the amount of substrate is increased during a chemical reaction?

Vmax is reached when all enzymes are saturated with substrate.

What is the main factor that can affect the rate of a reaction?

catalysis

Small molecules that are permanently attached to the surface of an enzyme and aid in its function are termed _____ groups.

prosthetic

In general, enzymes are composed of

proteins

The _____ inhibitors are common while the _____ inhibitors are uncommon.

reversible; irreversible