Chapter 8

Question 1

metabolism

Answer 1

The totality of an organism’s chemical reactions is called
metabolism (from the Greek metabole, change). Metabolism
is an emergent property of life that arises from orderly interactions between molecules

Question 2

what is a major pathway of cell resp

Answer 2

, in which the sugar glucose and other
organic fuels are broken down in the presence of oxygen to
carbon dioxide and water. (Pathways can have more than one
starting molecule and/or product.)

Question 3

s. Catabolic

and anabolic pathways are the

Answer 3

“downhill” and “uphill”

avenues of the metabolic landscape

Question 4

Energy is t

Answer 4

the capacity to cause change. In everyday life,
energy is important because some forms of energy can be used
to do work—that is, to move matter against opposing forces,
such as gravity and friction

Question 5

the man diving and his energy

Answer 5

The man diving is converting his potential energy to kinetic energy, which is then transferred to the water as he enters it, resulting in splashing, noise,
and increased movement of water molecules. A small amount
of energy is lost as heat due to friction

Question 6

what is an isolated system

Answer 6

. An isolated system, such as that approximated by
liquid in a thermos bottle, is unable to exchange either energy
or matter with its surroundings outside the thermos

Question 7

open system

Answer 7

. In an open
system, energy and matter can be transferred between the system and its surroundings. Organisms are open systems. They
absorb energy— release heat and metabolic
waste products, such as carbon dioxide, to the surroundings

Question 8

According to the first law of thermodynamics,

Answer 8

the
energy of the universe is constant: Energy can be transferred
and transformed, but it cannot be created or destroyed. The first
law is also known as the principle of conservation of energy.

Question 9

. Although order can increase locally, there is an

Answer 9

unstoppable trend toward randomization of the universe as

a whole.

Question 10

It turns out that if a given process, by itself, leads to an increase
in entropy, that process can

Answer 10

proceed without requiring an input of energy. Such a process is called a spontaneous process.
Note that as we’re using it here, the word spontaneous does
not imply that the process would occur quickly; rather, the
word signifies that it is energetically favorable.

Question 11

However, an organism also takes in organized forms of matter
and energy from the surroundings and replaces them with less
ordered forms. For example

Answer 11

an animal obtains starch, proteins, and other complex molecules from the food it eats. As
catabolic pathways break these molecules down, the animal
releases carbon dioxide and water—small molecules that possess less chemical energy than the food did (see Figure 8.3b).
The depletion of chemical energy is accounted for by heat
generated during metabolism. On a larger scale, energy flows
into most ecosystems in the form of light and exits in the form
of heat (see Figu

Question 12

The entropy of a particular system, such as an organism, may actually decrease as

Answer 12

long as the total entropy of the

universe—the system plus its surroundings—increases

Question 13

y. Free energy is the portion of

Answer 13

a system’s energy that can perform work when temperature
and pressure are uniform throughout the system, as in a living cell. Let’s consider how we determine the free-energy
change that occurs when a system changes—for example,
during a chemical reaction.

Question 14

Once we know the value of ∆G for a process, we can use it

to predict whether

Answer 14

r the process will be spontaneous (that is,
whether it is energetically favorable and will occur without
an input of energy)

Question 15

. More than a century of experiments has

shown that only processes with a negative ∆G are spontaneous. For ∆G to be negative, ∆

Answer 15

H must b negative too or T∆S must be positive

Question 16

n other words, every spontaneous

process decreases

Answer 16

the system’s free energy, and processes that

have a positive or zero ∆G are never spontaneous. pg 195

Question 17

Unstable systems (higher G) tend to change in such a way that

Answer 17

they become more stable (lower G)

Question 18

k. A process is spontaneous and can perform work only when

Answer 18

it is moving toward equilibrium.

Question 19

. An exergonic reaction

Answer 19

proceeds

with a net release of free energ

Question 20

one

of the defining features of life.

Answer 20

The fact that metabolism as a whole is never at equilibrium

Question 21

A cell does three main kinds of work

Answer 21

Chemical work, the pushing of endergonic reactions that
would not occur spontaneously, such as the synthesis
of polymers from monomers (chemical work will be discussed further here; examples are shown in Chapters 9
and 10)
Transport work, the pumping of substances across membranes against the direction of spontaneous movement
(see Concept 7.4)
Mechanical work, such as the beating of cilia (see
Concept 6.6), the contraction of muscle cells, and
the movement of chromosomes during cellular
reproduction

Question 22

. ATP contains the s

Answer 22

sugar ribose, with the nitrogenous base adenine and a chain of three phosphate
groups (the triphosphate group) bonded to it

Question 23

This is the free-energy change measured under standard conditions. In the cell, conditions do not conform to standard conditions, primarily bc

Answer 23

e reactant and product concentrations differ from 1 M. For example, when ATP hydrolysis
occurs under cellular conditions, the actual ∆G is about
-13 kcal/mol, 78% greater than the energy released by ATP
hydrolysis under standard conditions

Question 24

Because their hydrolysis releases energy, the phosphate
bonds of ATP are sometimes referred to as high-energy
phosphate bonds, but the term is misleading. T

Answer 24

The phosphate bonds of ATP are not unusually strong 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 ~P i). The release of energy during
the hydrolysis of ATP comes from the chemical change
of the system to a state of lower free energy, not from the
phosphate bonds themselves.

Question 25

phosphorylated intermediate.

Answer 25

The recipient molecule
with the phosphate group covalently bonded to it is then
called a phosphorylated intermediate. The key to
coupling exergonic and endergonic reactions is the formation of this phosphorylated intermediate, which is more

Question 26

Phosphorylation and dephosphorylation promote

Answer 26

crucial

protein shape changes during many other important cellular processes as well.

Question 27

If ATP could not be regenerated by

the phosphorylation of ADP,

Answer 27

humans would use up nearly

their body weight in ATP each day

Question 28

Without regulation by enzymes,

Answer 28

chemical traffic through the pathways of metabolism would
become terribly congested because many chemical reactions
would take such a long time. In the next two sections,
we will see why spontaneous reactions can be slow and
how an enzyme changes the situation

Question 29

activation energy

Answer 29

The initial investment of energy for starting a reaction—
the energy required to contort the reactant molecules so the
bonds can break—is known as the free energy of activation, or
activation energy, abbreviated EA in this book. We can
think of activation energy as the amount of energy needed to
push the reactants to the top of an energy barrier, or uphill, so
that the “downhill” part of the reaction can begin. Activation
energy is often supplied by heat in the form of thermal energy
that the reactant molecules absorb from the surroundings.

Question 30

catalysis

Answer 30

Instead of heat, organisms carry out
catalysis, a process by which a catalyst (for example, an
enzyme) selectively speeds up a reaction without itself being
consumed

Question 31

enzyme substrate complex

Answer 31

substrate. The enzyme binds to its substrate (or substrates, when there are two or more reactants), forming an
enzyme-substrate complex

Question 32

An enzyme is not a stiff structure locked into a given

shape. In fact,

Answer 32

recent work by biochemists has shown
that enzymes (and other proteins) seem to
“dance” between subtly different shapes in
a dynamic equilibrium, with slight differences in free energy for each “pose.”

Question 33

induced fit - d and what does it do

Answer 33

The tightening of the binding after initial contact—called
induced fit—is like a clasping handshake. Induced fit
brings chemical groups of the active site into positions that
enhance their ability to catalyze the chemical reaction.

Question 34

As the active site of an enzyme clutches the bound substrates, the enzyme may stretch the substrate molecules
toward their transition state form,

Answer 34

, stressing and bending
critical chemical bonds to be broken during the reaction.
Because EA is proportional to the difficulty of breaking
the bonds, distorting the substrate helps it approach the
transition state and reduces the amount of free energy
that must be absorbed to achieve that state.

Question 35

soon as the product exits an active site, another substrate molecule enters. At this substrate concentration, the
enzyme is said to be

Answer 35

saturated, and the rate of the reaction
is determined by the speed at which the active site converts
substrate to product. When an enzyme population is saturated, the only way to increase the rate of product formation is to add more enzyme. Cells often increase the rate of
a reaction by producing more enzyme molecules

Question 36

Up to a point, the rate of

an enzymatic reaction increases with increasing temperature, partly because…. what happens above that temp and why

Answer 36

substrates collide with active sites more
frequently when the molecules move rapidly. Above that
temperature, however, the speed of the enzymatic reaction
drops sharply. The thermal agitation of the enzyme molecule
disrupts the hydrogen bonds, ionic bonds, and other weak
interactions that stabilize the active shape of the enzyme, and
the protein molecule eventually denatures. E

Question 37

ach enzyme has

an optimal temperature at which … and what does this temp allow for

Answer 37

at which its reaction rate is greatest.
Without denaturing the enzyme, this temperature allows the
greatest number of molecular collisions and the fastest conversion of the reactants to product molecules. Most human
enzymes have optimal temperatures of about 35–40°C

Question 38

The

cofactors of some enzymes are

Answer 38

inorganic, such as the metal

atoms zinc, iron, and copper in ionic form

Question 39

coenzyme

Answer 39

If the cofactor
is an organic molecule, it is referred to, more specifically,
as a coenzyme. Most vitamins are important in nutrition
because they act as coenzymes or raw materials from which
coenzymes are made

Question 40

another word for comp inhibitors

Answer 40

mimics

Question 41

. In fact, molecules naturally present in

the cell often regulate enzyme activity by acting as inhibitors. why is this imp

Answer 41

Such regulation—selective inhibition—is essential to the control of cellular metabolism, a

Question 42

This simplified model is generally accepted as (pg 207)

Answer 42

he main way in
which the multitude of different enzymes arose over the past
few billion years of life’s history. Data supporting this model
have been collected by researchers using a lab procedure that
mimics evolution in natural population

Question 43

what would happen if all metabolic paths were going on at the same time

Answer 43

Chemical chaos would result if all of a cell’s metabolic pathways
were operating simultaneously. Intrinsic to life’s processes is a
cell’s ability to tightly regulate its metabolic pathways by controlling when and where its various enzymes are activ

Question 44

cooperativity

Answer 44

In another kind of allosteric activation, a substrate molecule binding to one active site in a multisubunit enzyme
triggers a shape change in all the subunits, thereby increasing catalytic activity at the other active sites (Figure 8.20b).
Called cooperativity, this mechanism amplifies the
response of enzymes to substrates: One substrate molecule primes an enzyme to act on additional substrate molecules
more readily. Cooperativity is considered allosteric regulation because, even though substrate is binding to an active
site, its binding affects catalysis in another active site.

Question 45

cell is

Answer 45

compartmentalized ( so enzymes and substrates are in specific locations and not thrown around randomly)

Question 46

In some cases, a team of

enzymes for several steps of a metabolic pathway are assembled into a multienzyme complex The arrangement facilitates

Answer 46

the sequence of reactions, with the product from the first
enzyme becoming the substrate for an adjacent enzyme in the
complex, and so on, until the end product is released. Some
enzymes and enzyme complexes have fixed locations within
the cell and act as structural components of particular membranes.

Question 47

Others are in solution within particular membraneenclosed eukaryotic organelles, each with

Answer 47

its own internal
chemical environment. For example, in eukaryotic cells, the
enzymes for the second and third stages of cellular respiration
reside in specific locations within mitochondria

Question 48

cell resp

Answer 48

the major catabolic pathway that breaks down organic molecules and releases energy
that can be used for the crucial processes of life.

Question 49

Chemical work (of a cell)

Answer 49

the pushing of endergonic reactions that
would not occur spontaneously, such as the synthesis
of polymers from monomers (chemical work will be discussed further here; examples are shown in Chapters 9
and 10)

Question 50

Transport work (of a cell)

Answer 50

the pumping of substances across membranes against the direction of spontaneous movement
(see Concept 7.4)

Question 51

Mechanical work

Answer 51

such as the beating of cilia (see
Concept 6.6), the contraction of muscle cells, and
the movement of chromosomes during cellular
reproduction