Biology Chapter 6
All cells use a molecule called to carry and release energy cyclically.
ATP
Which inhibitors bind to enzymes covalently?
irreversable
In broad terms, energy can exist in two states: energy and energy.
potential, kinetic
What molecule is a common energy source for living organisms?
ATP
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.
In order for molecules to achieve the transition state, energy is necessary.
activation
When enzymes and substrates bind and interact, this causes changes to occur that allow for a tighter fit between enzyme and substrate.
conformational
is the ability to promote change or do work.
energy
For living organisms, the total energy (H) is called , while the free energy (G) is the amount available to do work.
enthalpy
are a type of catalyst found in living cells that act to speed up chemical reactions.
enzymes
What must happen immediately before a reaction occurs with or without a catalyst?
A transition state must be reached.
Which of the following describes the hydrolysis of ATP?
A water molecule is added to ATP resulting in its breakdown to ADP and inorganic phosphate.
What is an induced fit between enzyme and substrate?
Conformational changes that cause enzyme and substrate to bind more tightly to one another
Name environmental factors that affect proper enzyme function.
Temperature, pH and ionic conditions
Select all of the statements that correctly describe endergonic reactions.
The products have higher free energy than the reactants. An input of energy is required.
What is enthalpy?
The total energy of a system
Which of these is an example of an object with high potential energy?
Water stored in a reservoir behind a dam
Why do organisms couple exergonic and endergonic reactions?
When exergonic and endergonic reactions are coupled, the endergonic reaction will proceed if the net free energy change is negative.
When will an endergonic and exergonic reaction that are coupled proceed spontaneously?
When the net free energy change for both reactions combined is negative (exergonic)
When does chemical equilibrium occur?
When the rate of formation of products equals the rate of formation of reactants
Where does a substrate bind on an enzyme in order for a chemical reaction to take place?
active site
What type of reaction or process occurs without needing an input of energy?
spontaneous
or reactants, are molecules that bind to an enzyme at the active site and are converted to products in chemical reactions.
substrates
Select the true statements about endergonic reactions.
-Endergonic reactions require the addition of free energy. -Endergonic reactions have a positive change in free energy. -The products have a higher free energy than the reactants. -Endergonic reactions are not spontaneous.
What causes the rate of some chemical reactions to be very slow?
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. Activation energy is required for molecules' bonds to be destabilized, and, therefore, products to be formed.
What is phosphorylation?
The transfer of a phosphate group from one molecule to another
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 are the two general functions of catabolic pathways?
To recycle the components of organic molecules for use in the synthesis of new molecules To obtain energy for use in endergonic processes
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
Select all of the following that describe metabolic pathways.
a different enzyme catalyzes each step can result in the synthesis of larger molecules from smaller molecules the product of one reaction becomes the substrate for the next reaction can result in the breakdown of large molecules
energy is the initial input of energy needed to overcome repulsion between molecules in a chemical reaction.
activation
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
Chemical occurs when the rate of formation of products equals the rate of formation of reactants.
equilibrium
When conformational changes cause enzyme and substrate to bind more tightly, this is called
induced fit
An enzyme accelerates the rate of a chemical reaction by:
lowering the activation energy
A(n) chemical reaction will proceed without the input of energy.
spontaneous
What best describes the range of pH where most enzymes function best?
A narrow range
Chemist Emil Fischer proposed that the interaction between enzyme and substrate resembled 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.
Which line on the graph indicates the activation energy in the presence of an enzyme for the reaction?
Blue line
The forward direction of the equation A+B → C+D shows that ______ are the products.
C+D
At what levels are metabolic pathways regulated?
Cellular Biochemical Genetic
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
Select the statements that are true of exergonic reactions.
Exergonic reactions release energy during product formation. Exergonic reactions are spontaneous.
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
Ribozymes are molecules.
RNA
How do reversible and irreversible inhibitors differ? Select all that apply.
Reversible inhibitors bind to enzymes noncovalently Irreversible inhibitors bind to enzymes covalently
What factors determine the direction and rate of a chemical reaction?
The change in free energy will determine the direction of the reaction. Catalysts influence the rate of a chemical reaction. Thermodynamics governs the direction of a reaction but not the rate of a reaction.
What is Vmax?
The maximal rate of a chemical reaction
The agent that speeds up the rate of a chemical reaction without being changed permanently is called
catalyst
inhibitors increase the KM of a reaction but do not change the Vmax.
competitive
During the breakdown of small organic molecules, oxidation occurs when
electrons are removed from an atom or molecule.
What is the term for the ability to do work?
energy
The three levels at which metabolic pathways are regulated are (1) regulation, (2) regulation, and (3) regulation.
genetic, cellular, biochemical
ATP hydrolysis can be used to drive chemical reactions because the hydrolysis of ATP has a ΔG that is:
negative
Small molecules that are permanently attached to the surface of an enzyme and aid in its function are termed groups.
prosthetic
Enzymes are typically composed of which type of macromolecule?
protein
In general, enzymes are composed of
proteins
A catalyst that is not made of protein is called a _______.
ribozyme
Almost all enzymes bind their substrates with a high degree of
specificity
Select all of the following that exhibit potential energy only.
A boulder sitting at the top of a hill A stretched rubber band Bow ready to fire an arrow Water at the top of a dam
Which of the following happens during phosphorylation involving glucose?
A phosphate group is transferred from ATP to glucose.
What is a substrate?
A reactant molecule that binds to the active site of an enzyme
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.
Which of the following accurately describes the role of conformational changes in enzyme-catalyzed reactions?
Enzymes undergo conformational changes that result in binding the substrate more tightly. Conformational changes are responsible for the induced fit between enzyme and substrate. Conformational changes must occur in order for an enzyme to catalyze the conversion of reactants to products.
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: When two reactions are coupled, the first reaction must always be exergonic for both to proceed exergonically.
False
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 of the following describes the major difference between kinetic and potential energy?
Kinetic energy is the energy of motion and potential energy is associated with the position of an object.
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.
What are prosthetic groups?
Small molecules permanently attached to the surface of an enzyme that aid in enzyme function
Which of the following are steps involved in an enzyme-catalyzed reaction?
Substrates are converted to products. Substrate binds to the enzyme at the active site. The enzyme undergoes conformational changes to bind the substrate more closely. Products are released from enzyme and enzyme is reused.
The hydrolysis of ATP can be used to drive a chemical reaction that cannot occur spontaneously because:
The hydrolysis of ATP has a negative ΔG. The hydrolysis of ATP is exergonic.
Select the best description of product formation in enzyme-catalyzed reactions:
Two steps: binding or release of substrate and product formation
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
Cells commonly use the hydrolysis of ______ to drive chemical reactions.
adenosine triphosphate
Anabolic reactions are also called reactions.
biosynthetic
Which line indicates an enzyme which is lowering the activation energy of the reaction may be present?
blue line
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
The two main functions of ______ pathways are to recycle components of macromolecules and to produce energy intermediates, such as ATP, which are directly used to drive ______ reactions in cells.
catabolic; endergonic
What is the main factor that can affect the rate of a reaction?
catalysis
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
Lowering the activation energy of a chemical reaction will:
change the rate of the reaction but will not change its direction
During reactions, one or more substances are changed or converted into other substances.
chemical
are small organic molecules that temporarily attach to an enzyme and promote a chemical reaction without being changed during the reaction.
coenzymes
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
In a chemical reaction, an enzyme's must change before it can catalyze the conversion of reactants to products.
conformation
What is affinity?
degree of attraction between the enzyme and substrate.
Increasing the temperature outside the optimal range for an enzyme can lead to of the enzyme, altering the enzyme's structure and function.
denaturation
Organisms couple and reactions because many vital cellular processes would not proceed without energy input.
endergonic, exergonic
When a water molecule is used to remove a phosphate group from ATP, this is called the of ATP.
hydrolysis
During what step in an enzyme catalyzed reaction is the activation energy lowered?
induced fit
The general term for all types of coordinated sequences of chemical reactions that occur in cells is pathways.
metabolic
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
Put each experimental step in the correct order for an experiment testing the effect of substrate concentration on the rate of an enzymatic reaction.
place 1 incubate measure
Metabolic pathways can be categorized according to whether the sequence of coordinated chemical reactions leads to the or of substances.
synthesis, breakdown
Consider the reversible reaction: A + B ↔ C + D. Whether C + D are favored over A + B will depend upon:
the concentrations of reactants and products the energy input required
Many of the chemical reactions that occur in cells are endergonic. These reactions are possible because they are coupled to:
the hydrolysis of ATP
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
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
When a reactant binds to the active site of an enzyme, this produces the enzyme- complex.
substrate
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.
What are the two main factors that determine the outcome of a chemical reaction in a living cell?
direction and rate
A reaction is said to be when the addition of free energy from the environment is required for the reaction to proceed.
endergonic
Work in the cell or in the physical world can only be done with expenditure of ; it is defined as the capacity to do work.
energy
are a type of catalyst found in living cells that acts to speed up chemical reactions.
enzymes
Catalyzed reactions occur at ______ rate compared to uncatalyzed reactions.
faster
The rates of enzyme-catalyzed reactions are typically millions of times than corresponding uncatalyzed reactions.
faster
What is the term used to describe the energy of a system that is available to do work?
free energy
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
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
List the following steps of an enzyme-catalyzed reaction in order, beginning with the first step at the top.
substrates bind the enzyme substrates are products
What is produced by the binding of enzyme and substrate?
Enzyme-substrate complex
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.
How do enzymes lower the activation energy of a chemical reaction?
Enzymes can bring reactants closer together. When reactants are bound to enzymes, they can be strained, making it easier to achieve the transition state.
Select all of the following that can take place during a chemical reaction.
-Molecules attach to each other to form larger molecules. -Molecules are broken apart. -Electrons are transferred between atoms. -Rearrangements of atoms within molecules occur.
What happens when the transition state is reached? Select all that apply.
Bonds are stretched to their limit in the reactant molecules. The chemical reaction can readily proceed.
Why do catalysts increase the rate of a chemical reaction?
Catalysts lower the activation energy.
Which of the following are ways that enzymes act to increase the rate of a chemical reaction?
Changing the local environment of the reactants Positioning the reactants very close to each other Lowering the activation energy Straining the bonds in the reactants
How can the functioning of an enzyme be affected by the external environment?
Increasing the temperature can greatly affect the functioning of some enzymes by causing denaturation. Altering the pH can be harmful to an enzyme when the pH is outside the normal or optimal range for that enzyme.
What are the two general forms in which energy exists?
Kinetic energy and potential energy
During which step during an enzyme-catalyzed reaction does the initial conformational change occur?
When substrate binds to the active site, causing an induced fit
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, plateau
Enzymes increase the rate of a chemical reaction by the activation energy.
lowering
Direction and are the two main factors that determine the fate of a chemical reaction.
rate