Chapter 8

endergonic reaction

("energy inward") absorbs free energy from the surroundings

exergonic reaction

("energy outward") proceeds with a net release of free energy to the surroundings

Entropy

A measure of disorder or randomness.

catabolic pathway

A metabolic pathway that releases energy by breaking down complex molecules to simpler compounds.

spontaneous process

A process that occurs without an overall input of energy; a process that is energetically favorable.

Which of the following statements about equilibrium of chemical reactions is correct?

A reaction that is at equilibrium is not capable of doing any work. The ΔG for a reaction at equilibrium is zero, which means that there is no free energy available to do any work.

E+S

E+S-> ES -> E + P -- The enzyme is not completely used up in the reactions

first law of thermodynamics (law of conservation of energy)

Energy can be transferred and transformed, but it cannot be created or destroyed The first law is also called the principle of conservation of energy

first law of thermodynamics

Energy can be transferred and transformed, but it cannot be created or destroyed.

Which of the following statements about enzyme function is true?

Enzymes increase the rate of chemical reactions by lowering activation energy barriers.

second law of thermodynamics

Every energy transfer or transformation increases the entropy (disorder) of the universe. or heat flows spontaneously from warmer object to cooler object

second law of thermodynamics

Every energy transfer or transformation increases the entropy of the universe Entropy is a measure of molecular disorder, or randomness; During every energy transfer or transformation, some energy is converted to thermal energy and lost as heat, becoming unavailable to do work

What type of reaction breaks the bonds that join the phosphate groups in an ATP molecule?

Hydrolysis; Hydrolysis involves breaking bonds with the addition of water.

anabolic pathways

Metabolic pathways that consume energy to build complicated molecules from simpler ones; For example, the synthesis of protein from amino acids is an anabolic pathway

Unspontaneous process

Processes that decrease entropy are nonspontaneous; they require an input of energy

energy

The ability to do work or cause change

Which of the following is NOT a way in which an enzyme can speed up the reaction that it catalyzes?

The active site can provide heat from the environment that raises the energy content of the substrate.; An enzyme cannot extract heat from the environment to speed a reaction. It can only lower the activation energy barrier so that more substrates have the energy to react.

Which of the following is true when comparing an uncatalyzed reaction to the same reaction with a catalyst?

The catalyzed reaction will have the same Δ_G_.

The binding of a compound to an enzyme is observed to slow down or stop the rate of the reaction catalyzed by the enzyme. Increasing the substrate concentration reduces the inhibitory effects of this compound. Which of the following could account for this observation? See Concept 8.4 (Page)

The compound is a competitive inhibitor.; A competitive inhibitor slows down the enzyme by competing with the substrate for binding at the active site. Increasing substrate concentrations will reduce the effectiveness of a competitive inhibitor.

Which of the following statements about ATP (adenosine triphosphate) is correct?

The cycling between ATP and ADP + Pi provides an energy coupling between catabolic and anabolic pathways; Catabolic pathways provide the energy needed to make ATP from ADP and Pi. The hydrolysis of ATP to ADP + Pi releases the same amount of energy.

Which of the following statements about the role of ATP in cell metabolism is true?

The energy from the hydrolysis of ATP may be directly coupled to endergonic processes by the transfer of the phosphate group to another molecule.; A key feature in the way cells manage their energy resources to do this work is energy coupling, the use of an exergonic process to drive an endergonic one. ATP is responsible for mediating most energy coupling in cells, and in most cases it acts as the immediate source of energy that powers cellular work. Read about energy coupling.

heat

The energy transferred between objects that are at different temperatures

Which of the following statements about the combustion of glucose with oxygen to form water and carbon dioxide (C6H12O6 + 6 O2 → 6 CO2 + 6 H2O) is correct? See Concept 8.2 (Page)

The entropy of the products is greater than the entropy of the reactants.; A large molecule (glucose) has been converted into several smaller molecules (water and carbon dioxide); thus, the products have more disorder (greater entropy) than the reactants.

Which of the following would be unlikely to contribute to the substrate specificity of an enzyme?

The enzyme has an allosteric regulatory site; The allosteric site is distinct from the active site, and does not affect the substrate specificity of the enzyme.

Which of the following statements about feedback regulation of a metabolic pathway is correct?

The final product of a metabolic pathway is usually the compound that regulates the pathway.; It is quite common that the end product of the pathway controls the overall rate of the pathway.

Which of the following statements about feedback regulation of a metabolic pathway is correct? See Concept 8.5 (Page)

The final product of a metabolic pathway is usually the compound that regulates the pathway.; It is quite common that the end product of the pathway controls the overall rate of the pathway.

Enthalpy

The heat content of a system at constant pressure

activation energy (EA)

The initial energy needed to break the bonds of the reactants is called

substrate

The reactant that an enzyme acts on is called the enzyme's

Which of the following statements is true for a system at chemical equilibrium?

The system can do no work.

energy coupling

The use of an exergonic process to drive an endergonic one. Most energy coupling in cells is mediated by ATP

Free energy change

The ΔG for a process can be used to determine whether it is spontaneous or not ΔG is negative for all spontaneous processes ΔG is zero or positive for nonspontaneous processes Every spontaneous process decreases the system's free energy Spontaneous processes can be harnessed by the cell to perform work

The Laws of Energy Transformation

Thermodynamics is the study of energy transformations. According to the first law of thermodynamics, the energy of the universe is constant. Energy can be transferred and transformed, but it cannot be created or destroyed. According to the second law of thermodynamics, every energy transfer or transformation increases the entropy (disorder) of the universe.

enzyme-substrate complex

When an enzyme binds to its substrate, it forms:

When chemical, transport, or mechanical work is done by an organism, what happens to the heat generated?

When chemical, transport, or mechanical work is done by an organism, what happens to the heat generated?

Which statement about the binding of enzymes and substrates is correct?

When substrate molecules bind to the active site of the enzyme, the enzyme undergoes a slight change in shape; As the substrate enters the active site, the enzyme changes shape slightly due to interactions between the substrate's chemical groups and chemical groups on the side chains of the amino acids that form the active site. This shape change makes the active site fit even more snugly around the substrate. This induced fit is like a clasping handshake.

During a laboratory experiment, you discover that an enzyme-catalyzed reaction has a ∆G of -20 kcal/mol. If you double the amount of enzyme in the reaction, what will be the ∆G for the new reaction?

Will remain the same; -20 kcal/mol

The process of cellular respiration, which converts simple sugars such as glucose into CO2 and water, is an example of _____. See Concept 8.1 (Page)

a catabolic pathway; Cellular respiration is a catabolic pathway.

Zinc, an essential trace element for most organisms, is present in the active site of the enzyme carboxypeptidase. The zinc most likely functions as _____.

a cofactor necessary for enzyme activity

enzyme catalysis

a reaction by lowering the EA barrier enough for the reaction to occur at moderate temperatures; An enzyme cannot change ΔG; it only speeds up a reaction that would eventually occur anyway

ATP cycle

a revolving door through which energy passes during its transfer from catabolic to anabolic pathways

thermal energy

is the kinetic energy associated with random movement of atoms or molecules Thermal energy in transfer from one object to another is called heat Light is another type of energy that can be harnessed to do work, such as photosynthesis

free energy

is the portion of a system's energy that can do work when temperature and pressure are uniform throughout the system, as in a living cell

active site

is the region on the enzyme, often a pocket or groove, that binds to the substrate

As a result of its involvement in a reaction, an enzyme _____.

is unchanged; Enzymes are not changed as a result of their participation in a reaction.

delta S

measure of disorder (entropy)

spontaneous process

occur without energy input; they can happen quickly or slowly

In general, enzymes are what kinds of molecules?

proteins

transport work

pumping substances across membranes against the direction of spontaneous movement

Enzymes work by _____.

reducing EA

catabolic pathways

release energy by breaking down complex molecules into simpler compounds

ΔG

represents the difference between free energy of the final state and free energy of the initial state ΔG = Gfinal state - Ginitial state If a reaction has negative ΔG, the system loses free energy and becomes more stable

induced fit

results from interactions between chemical groups on the substrate and the active site

activation energy barrier

separates the reactants from the products; reactants must overcome this in order to become products

metabolic pathways are

sequences of enzymatically catalyzed chemical reactions in a cell. Each step is a different enzyme

potential energy

stored energy that results from the position or shape of an object

What name is given to the reactants in an enzymatically catalyzed reaction?

substrate; This is the name given to the reactants in an enzymatically catalyzed reaction.

Reactions in closed system

such as an isolated hydroelectric system, eventually reach equilibrium and can then do no work

Mechanical work

such as beating cilia or contracting muscle cells

cellular respiration

the breakdown of glucosein the presence of O2, is an example of a pathway of catabolism

Energy

the capacity to cause change, can be used to do work—move matter against opposing forces, such as gravity and friction 1. Energy exists in various forms 2. Living cells must transform energy from one form to another to do the work of life

Energy is observed in two basic forms: potential and kinetic. Which of the following correctly matches these forms with a source of energy? See Concept 8.1 (Page)

the covalent bonds of a sugar molecule: potential energy; Bonds are a form of potential energy because the energy arises from the relative positions of the atoms that form the bond.

Gibbs free energy

the energy of a system that is available to do work at a constant temperature and pressure

Equilibrium

the point at which forward and reverse reactions occur at the same rate, describes a state of maximum stability; Systems never spontaneously move away from equilibrium A process is spontaneous and can perform work only when it is moving toward equilibrium

Chemical work

the pushing of endergonic reactions that would not occur spontaneously

Metabolism

the totality of an organism's chemical reactions

When is energy released from ATP?

when the terminal phosphate bond is broken by hydrolysis, the addition of a water molecule.

Which part of the adenosine triphosphate molecule is released when it is hydrolyzed to provide energy for biological reactions?

γγ-phosphate (the terminal phosphate)

The figure illustrates the energy states associated with the reaction A + B ↔ C + D. Which of the following terms best describes the forward reaction in the figure?

exergonic, G < 0

-ase

forms names of enzymes;he enzyme sucrase catalyzes the hydrolysis of sucrose into glucose and fructose

Delta G

free energy (spontaneous)

Delta H

heat flow (enthralpy)

inorganic cofactors

include metal atoms such as zinc, iron, and copper in ionic form

Enzymes are described as catalysts, which means that they _____.

increase the rate of a reaction without being consumed by the reaction; This permits enzyme molecules to be used repeatedly.

catalyst

is a chemical agent that speeds up a reaction without being consumed by the reaction

enzyme

is a macromolecule (typically protein) that acts as a catalyst to speed up a specific reaction. For example, adding the enzyme sucrase to a sucrose solution at room temperature will catalyze the complete hydrolysis of sucrose within seconds

An enzyme _____.

is an organic catalyst; Enzymes are proteins that behave as catalysts

kinetic energy

is energy associated with motion; Moving objects perform work by imparting motion to other matter For example, water gushing through a dam turns turbines

Phosphorlated Intermediate

is more reactive (less stable, with more free energy) that the original molecule

Effects of Local Conditions on Enzyme Activity

- Enzymes are pH and temp sensitive - Optimal activity occurs at a specific pH range and temperature EX for temperature: - When you have a fever, digestive enzymes are denatured --> why it's difficult to eat while sick

Regeneration of ATP

-ATP is a renewable resource that is regenerated by addition of a phosphate group to adenosine diphosphate (ADP) -The energy to phosphorylate ADP comes from catabolic reactions in the cell -The ATP cycle is a revolving door through which energy passes during its transfer from catabolic to anabolic pathways

Which of the following is the most correct interpretation of the figure?

ATP is a molecule that acts as an intermediary to store energy for cellular work.

highest energy form of adenosine from the following images.

Adenosine triphosphate (ATP) is the high-energy form of adenosine because it contains the most phosphate groups (three). This molecule fuels many different endergonic (energy-requiring) enzymatic processes in biological organisms. ATP molecules diffuse or are transported to the place where the energy is needed and deliver chemical energy from the breaking of their phosphate bonds.

change in free energy

Change in free energy during a reaction is related to temperature and changes in enthalpy and entropy ΔG = ΔH - TΔS ΔG = change in free energy ΔH = change in enthalpy (total energy) ΔS = change in entropy T = Temperature in Kelvin (K)

A cell does three main kinds work______

Chemical work Transport work Mechanical work

What is the name of the thermodynamic barrier that must be overcome before products are formed in a spontaneous reaction?

activation energy

cofactors

are nonprotein helpers that bind to the enzyme permanently, or reversibly with the substrate

How does a noncompetitive inhibitor decrease the rate of an enzyme-catalyzed reaction?

by binding to an allosteric site, thus changing the shape of the active site of the enzyme

How can enzyme catalyzed be sped up?

by increasing substrate concentration; When all enzyme molecules have their active sites engaged, the enzyme is saturated If the enzyme is saturated, the reaction rate can only be sped up by adding more enzyme

open system

energy and matter can be transferred between the system and its surroundings; Organisms are open systems; they absorb energy from light or food and release heat and metabolic wastes, such as CO2, to the surroundings

Which of the following terms most precisely describes the cellular process of breaking down large molecules into smaller ones?

catabolism (catabolic pathways)

ΔH

change in enthalpy (total energy)

ΔS

change in entropy

ΔG

change in free energy

What is the correct label for "A"?

energy of activation

kinetic energy

energy of motion

free energy

energy that is available to do work

Living organisms increase the disorder of their surroundings through their metabolism

ex. the breakdown of food releases heat and small molecules, such as CO2

HIV is the virus that causes AIDS. In the mid-1990s, researchers discovered an enzyme in HIV called protease. Once the enzyme's structure was known, researchers began looking for drugs that would fit into the active site and block it. If this strategy for stopping HIV infections were successful, it would be an example of what phenomenon?

competitive inhibition

A chemical reaction that has a positive ΔG is best described as _____.

endergonic