Chapter 8 Flashcards
metabolism
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
what is a major pathway of cell resp
, 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.)
s. Catabolic
and anabolic pathways are the
“downhill” and “uphill”
avenues of the metabolic landscape
Energy is t
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
the man diving and his energy
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
what is an isolated system
. 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
open system
. 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
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. The first
law is also known as the principle of conservation of energy.
. Although order can increase locally, there is an
unstoppable trend toward randomization of the universe as
a whole.
It turns out that if a given process, by itself, leads to an increase
in entropy, that process can
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.
However, an organism also takes in organized forms of matter
and energy from the surroundings and replaces them with less
ordered forms. For example
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
The entropy of a particular system, such as an organism, may actually decrease as
long as the total entropy of the
universe—the system plus its surroundings—increases
y. 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. Let’s consider how we determine the free-energy
change that occurs when a system changes—for example,
during a chemical reaction.
Once we know the value of ∆G for a process, we can use it
to predict whether
r the process will be spontaneous (that is,
whether it is energetically favorable and will occur without
an input of energy)
. More than a century of experiments has
shown that only processes with a negative ∆G are spontaneous. For ∆G to be negative, ∆
H must b negative too or T∆S must be positive
n other words, every spontaneous
process decreases
the system’s free energy, and processes that
have a positive or zero ∆G are never spontaneous. pg 195
Unstable systems (higher G) tend to change in such a way that
they become more stable (lower G)
k. A process is spontaneous and can perform work only when
it is moving toward equilibrium.
. An exergonic reaction
proceeds
with a net release of free energ
one
of the defining features of life.
The fact that metabolism as a whole is never at equilibrium
A cell does three main kinds of work
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
. ATP contains the s
sugar ribose, with the nitrogenous base adenine and a chain of three phosphate
groups (the triphosphate group) bonded to it
This is the free-energy change measured under standard conditions. In the cell, conditions do not conform to standard conditions, primarily bc
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
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
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.
