Ch 6: An Introduction to Metabolism Flashcards

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1
Q

What is a catabolic pathway?

A

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

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2
Q

What type of metabolic pathway consumes energy to build complicated molecules from simpler ones?

A

Anabolic pathway

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3
Q

What is bioenergetics?

A

The study of how energy flows through living organisms.

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4
Q

Gibbs free energy is the portion of a system’s energy that can perform work when temperature and pressure are uniform throughout the system, as in a living cell. The expression ΔG is given by:

A

ΔG = Gfinal state - Ginitial state

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5
Q

Much research has shown that only reactions with a negative ΔG can occur with no input of energy, so the value of ΔG tells us whether a particular reaction is a ___________ one.

A

spontaneous

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6
Q

For a reaction to have a negative ΔG, the system must lose free energy during the change from initial state to final state. Because it has less free energy, the system in its final state is less likely to change and is therefore ____ ______ than it was previously. We can think of free energy as a measure of a system’s ___________—its tendency to change to a more stable state. Unstable systems (higher G) tend to change in such a way that they become more stable (lower G)

A

more stable

instability

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7
Q

For a system at equilibrium, G is at its ______ ________ value in that system. We can think of the equilibrium state as a free-energy valley. Any change from the equilibrium position will have a positive ΔG and will not be __________.

A

lowest possible

spontaneous

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8
Q

Because a system at equilibrium cannot spontaneously change, it can do __ ____. A process is spontaneous and can perform work only when it is moving toward equilibrium.

A

no work

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9
Q

Based on their free-energy changes, chemical reactions can be classified as either exergonic (“energy outward”) or endergonic (“energy inward”). An exergonic reaction proceeds with a net release of free energy. Because the chemical mixture loses free energy (G decreases), ΔG is ________ for an exergonic reaction. Using ΔG as a standard for spontaneity, exergonic reactions are those that occur spontaneously. The magnitude of ΔG for an exergonic reaction represents the maximum amount of work the reaction can perform (some of the free energy is released as heat and cannot do work). The _______ the decrease in free energy, the greater the amount of work that can be done.

A

negative

greater

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10
Q

An endergonic reaction requires energy input, and thus is, by definition, ___________.

A

nonspontaneous

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11
Q

The overall reaction for cellular respiration is:

C6H12O6 + 6 O2 → 6 CO2 + 6 H2O

686 kcal (2,870 kJ) of energy are made available for work for each mole (180 g) of glucose broken down by respiration under “standard conditions” (1 M of each reactant and product, 25°C, pH 7). Because energy must be conserved, the products of respiration store 686 kcal less ____ ______ per mole than the reactants. The products are the “exhaust” of a process that tapped the free energy stored in the bonds of the sugar molecules.

A

free energy

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12
Q

It is important to realize that the breaking of bonds does ___ _______ ______; on the contrary, as you will soon see, it requires energy. The phrase “energy stored in bonds” is shorthand for the potential energy that can be released when new bonds are formed after the original bonds break, as long as the products are of lower free energy than the reactants.

A

not release energy

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13
Q

An endergonic reaction is one that absorbs free energy from its surroundings. Because this kind of reaction essentially ______ free energy in molecules (G increases), ΔG is positive. Such reactions are nonspontaneous, and the magnitude of ΔG is the quantity of energy required to drive the reaction. If a chemical process is exergonic (downhill), releasing energy in one direction, then the reverse process must be endergonic (uphill), using energy.

A

stores

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14
Q

If ΔG = −686  kcal/mol for respiration, which converts glucose and oxygen to carbon dioxide and water, then the reverse process—the conversion of carbon dioxide and water to glucose and oxygen—must be strongly endergonic, with ΔG = +686  kcal/mol. Such a reaction would never happen by itself.

How, then, do plants make sugar? They get the required energy (686 kcal to make a mole of glucose) by capturing light from the sun and converting its energy to ________ energy. Next, in a long series of exergonic steps, they gradually spend that chemical energy to ________ glucose molecules.

A

chemical

assemble

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15
Q

Because systems at equilibrium are at a minimum of G and can do no work, a cell that has reached metabolic equilibrium is dead! The fact that metabolism as a whole is never at equilibrium is one of the defining features of ____.

A

life

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16
Q

What are the 3 main kinds of work done by a cell?

A

chemical work

transport work

mechanical work

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17
Q

A key feature in the way cells manage their energy resources to do this work is energy coupling, the use of an _________ _______ to drive an __________ 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.

A

exergonic process

endergonic

18
Q

The bonds between the phosphate groups of ATP can be broken by hydrolysis. When the terminal phosphate bond is broken by the addition of a water molecule, a molecule of inorganic phosphate (HOPO32−, abbreviated Pi throughout this book) leaves the ATP. In this way, adenosine triphosphate becomes adenosine diphosphate, or ADP.

A
19
Q

Because their hydrolysis releases energy, the phosphate bonds of ATP are sometimes referred to as high-energy phosphate bonds, but the term is misleading. The phosphate bonds of ATP are not unusually ______ bonds, as “high-energy” may imply; rather, the reactants (ATP and water) themselves have high energy relative to the energy of the products (ADP and Pi). The release of energy during the hydrolysis of ATP comes from the chemical change to a state of _____ free energy, not from the phosphate bonds themselves.

A

strong

lower

20
Q

But why does the hydrolysis of ATP release so much energy? If we reexamine the ATP molecule, we can see that all three phosphate groups are negatively charged. These like charges are crowded together, and their mutual __________ contributes to the instability of this region of the ATP molecule. The triphosphate tail of ATP is the chemical equivalent of a __________ ______.

A

repulsion

compressed spring

21
Q

Because both directions of a reversible process cannot be downhill, the generation of ATP from ADP and Pi is necessarily __________.

A

endergonic

p. 134

22
Q

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

A

hydrolysis

23
Q

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

The phosphate bonds of ATP are unusually strong bonds.

The free energy released by ATP hydrolysis has a much more negative ΔGΔG value than the hydrolysis of phosphate groups from other phosphorylated molecules.

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

The energy from the hydrolysis of ATP may be directly coupled to endergonic processes by the transfer of the phosphate group to another molecule.

24
Q

Enzymes work by…

A

…reducing the energy of activation.

25
Q

True or False?

Substrate molecules fit into the active site of an enzyme like a key fits into a lock.

A

False. 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.

26
Q

Because they bind directly to the active site by covalent bonds, irreversible inhibitors __________ render an enzyme inactive. Some drugs are irreversible inhibitors, including the antibiotic penicillin (which inhibits an enzyme involved in bacterial cell-wall synthesis) and aspirin (which inhibits cyclooxygenase-2, the enzyme involved in the inflammatory reaction).

A

permanently

27
Q

Which of the following is true of energy coupling?

a. ) is the hydrolysis of ATP to ADP + P
b. ) involves transfer of a phosphate group from ATP to a reactant in an endergonic reaction
c. ) can be a barrier to the initiation of a reaction
d. ) is the use of an enzyme to reduce activation energy

A

b.) involves transfer of a phosphate group from ATP to a reactant in an endergonic reaction

28
Q

The active site itself is also not a _____ receptacle for the substrate. 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 ______ site fit even more snugly around the substrate.

A

rigid

active

29
Q

What is this tightening of the binding (of the substrate to the active site) after initial contact called? This is like a clasping handshake, and it brings chemical groups of the active site into positions that enhance their ability to catalyze the chemical reaction.

30
Q

What is a cofactor?

A

Any nonprotein molecule or ion that is required for the proper functioning of an enzyme. Cofactors can be permanently bound to the active site or may bind loosely and reversibly, along with the substrate, during catalysis.

31
Q

Where does a noncompetitive inhibitor bind?

A

To a site other than the active site (which then changes the shape of the enzyme’s active site)

32
Q

Questions from bio lab experiment on enzymes:

Starch is a _______ of glucose that is a carbohydrate reserve in plants, and is hydrolyzed by the enzyme amylase. Thus, starch is a _________ for amylase.

A

polymer

substrate

33
Q

Molecules naturally present in the cell regulate enzyme activity by acting as inhibitors. Such regulation – _________ __________ – is essential to the control of cellular metabolism.

A

selective inhibition

34
Q

__________ ___________ is the term used to describe any case in which a protein’s function at one site is affected by the binding of a regulatory molecule to a separate site. It may result in either inhibition or stimulation of an enzyme’s activity.

A

Allosteric regulation

35
Q

In the simplest kind of allosteric regulation, an activating or inhibiting regulatory molecule binds to a __________ site (sometimes called an allosteric site), often located where subunits join. The binding of an activator to a regulatory site stabilizes the shape that has functional active sites, whereas the binding of an inhibitor stabilizes the ________ ____ of the enzyme.

A

regulatory

inactive form

36
Q

[In regards to allosteric regulation]

Through this interaction of subunits, a single activator or inhibitor molecule that binds to one regulatory site will affect the active sites of ___ ________.

A

all subunits

37
Q

Cooperativity is another kind of allosteric activation. This happens when the binding of one substrate molecule to the active site of one subunit _____ ALL subunits in ______ conformation.

A

locks

active

38
Q

Cooperativity is considered allosteric regulation because even though substrate is binding to an active site, its binding affects catalysis in _______ active site.

A

another

39
Q

There is a common mode of metabolic control, called feedback inhibition, in which a metabolic pathway is halted by the inhibitory binding of its ___ _______ to an enzyme that acts early in the pathway.

A

end product

40
Q

The overall reaction for cellular respiration shows that this is an exergonic/endergonic reaction:

C6H12O6 + 6O2 → 6CO2 + 6H2O

ΔG = -686 kcal/mol (-2,870 kJ/mol)

A

exergonic reaction, bc ΔG is negative

41
Q

What can’t most cells harness heat to perform work?

A

Because a system can put thermal energy to work only when there is a temperature difference that results in the thermal energy flowing as heat from a warmer location to a cooler one. If temperature is uniform, as it is in a living cell, then the heat generated during a chemical reaction will simply warm a body of matter, such as the organism.

p. 128