Transcript Energy

BIOLOGY Life on Earth
WITH PHYSIOLOGY Tenth Edition
Audesirk Audesirk Byers
6
Energy Flow in
the Life of a Cell
Lecture Presentations by
Carol R. Anderson
Westwood College, River Oaks Campus
© 2014 Pearson Education, Inc.
Chapter 6 At a Glance
 6.1 What Is Energy?
 6.2 How Is Energy Transformed During Chemical
Reactions?
 6.3 How Is Energy Transported Within Cells?
© 2014 Pearson Education, Inc.
6.1 What Is Energy?
 Energy is the capacity to do work
 Work is a transfer of energy to an object, which
causes the object to move
© 2014 Pearson Education, Inc.
6.1 What Is Energy?
 Chemical energy is the energy that is contained in
molecules and released by chemical reactions
– Molecules that provide chemical energy include
sugar, glycogen, and fat
– Cells use specialized molecules such as ATP to
accept and transfer energy from one chemical
reaction to the next
© 2014 Pearson Education, Inc.
6.1 What Is Energy?
 There are two fundamental types of energy
– Potential energy is stored energy
– For example, the chemical energy in bonds, the
electrical charge in a battery, and a penguin poised to
plunge
– Kinetic energy is the energy of movement
– For example, light, heat, electricity, and the movement
of objects
© 2014 Pearson Education, Inc.
Figure 6-1 Converting potential energy to kinetic energy
© 2014 Pearson Education, Inc.
6.1 What Is Energy?
 The laws of thermodynamics describe the basic
properties of energy
– The laws describe the quantity (the total amount) and the
quality (the usefulness) of energy
– Energy can neither be created nor destroyed (the first law
of thermodynamics), but can change form
– The first law is often called the law of conservation of
energy
– The total amount of energy within a closed system
remains constant unless energy is added or removed
from the system
© 2014 Pearson Education, Inc.
6.1 What Is Energy?
 The laws of thermodynamics describe the basic
properties of energy (continued)
– The amount of useful energy decreases when energy
is converted from one form to another (the second
law of thermodynamics)
– Entropy (disorder) is the tendency to move toward a
loss of complexity and of useful energy and toward an
increase in randomness, disorder, and less-useful
energy
© 2014 Pearson Education, Inc.
6.1 What Is Energy?
 The laws of thermodynamics describe the basic
properties of energy (continued)
– Useful energy tends to be stored in highly organized
matter, and when energy is used in a closed system
(such as the world in which we live), there is an
overall increase in entropy
– For example, when gasoline is burned, the orderly
arrangement of eight carbons bound together in a
gasoline molecule are converted to eight randomly
moving molecules of carbon dioxide
© 2014 Pearson Education, Inc.
Figure 6-2 Energy conversions result in a loss of useful energy
Combustion
by engine
gas
100 units chemical
energy
© 2014 Pearson Education, Inc.
80 units  20 units kinetic energy
heat energy
6.1 What Is Energy?
 Living things use the energy of sunlight to create the
low-entropy conditions of life
– The highly organized low-entropy systems of life do
not violate the second law of thermodynamics
because they are achieved through a continuous
influx of usable light energy from the sun
– In creating kinetic energy in the form of sunlight, the
sun also produces vast entropy as heat
© 2014 Pearson Education, Inc.
6.2 How Is Energy Transformed During Chemical
Reactions?
 A chemical reaction is a process that forms or
breaks the chemical bonds that hold atoms together
– Chemical reactions convert one set of chemical
substances, the reactants, into another set, the
products
– All chemical reactions either release energy or require
a net input of energy
– Exergonic reactions release energy
– Endergonic reactions require an input of energy
© 2014 Pearson Education, Inc.
Figure 6-3 An exergonic reaction
energy
reactants
products
© 2014 Pearson Education, Inc.
Figure 6-4 An endergonic reaction
energy
products
reactants
© 2014 Pearson Education, Inc.
6.2 How Is Energy Transformed During Chemical
Reactions?
 Exergonic reactions release energy
– Reactants contain more energy than products in
exergonic reactions
– An example of an exergonic reaction is the burning of
glucose
– As glucose is burned, the sugar (C6H12O6) combines
with oxygen (O2) to produce carbon dioxide (CO2) and
water (H2O), releasing energy
– Because molecules of sugar contain more energy than
do molecules of carbon dioxide and water, the reaction
releases energy
© 2014 Pearson Education, Inc.
Figure 6-5 Reactants and products of burning glucose
energy
C6H12O6  6 O2
(glucose) (oxygen)
6 CO2  6 H2O
(water)
(carbon
dioxide)
© 2014 Pearson Education, Inc.
6.2 How Is Energy Transformed During Chemical
Reactions?
 Endergonic reactions require a net input of energy
– The reactants in endergonic reactions contain less
energy than the products
– An example of an endergonic reaction is
photosynthesis
– In photosynthesis, green plants add the energy of
sunlight to the lower-energy reactants water and carbon
dioxide to produce the higher-energy product sugar
© 2014 Pearson Education, Inc.
Figure 6-6 Photosynthesis
energy
C6H12O6  6 O2
(glucose) (oxygen)
6 CO2  6 H2O
(water)
(carbon
dioxide)
© 2014 Pearson Education, Inc.
6.2 How Is Energy Transformed During Chemical
Reactions?
 Endergonic reactions require a net input of energy
(continued)
– All chemical reactions require an initial energy input
(activation energy) to get started
– The negatively charged electron shells of atoms repel
one another and inhibit bond formation
– Molecules need to be moving with sufficient collision
speed to overcome electronic repulsion and react
– Increasing the temperature will increase kinetic energy
and, thus, the rate of reaction
© 2014 Pearson Education, Inc.
Figure 6-7 Activation energy in an exergonic reaction
Activation energy required
to start the reaction
high
energy level of reactants
energy
content
of
molecules
reactants
energy level of products
products
low
progress of reaction
An exergonic reaction
© 2014 Pearson Education, Inc.
Sparks ignite gas
6.3 How Is Energy Transported Within Cells?
 Most organisms are powered by the breakdown of
glucose
 Energy in glucose cannot be used directly to fuel
endergonic reactions
 Energy released by glucose breakdown is first
transferred to an energy-carrier molecule
– Energy-carrier molecules are high-energy, unstable
molecules that are synthesized at the site of an
exergonic reaction, capturing some of the released
energy
© 2014 Pearson Education, Inc.
6.3 How Is Energy Transported Within Cells?
 ATP and electron carriers transport energy within
cells
– Adenosine triphosphate (ATP) is the most common
energy-carrying molecule
– ATP is composed of the nitrogen-containing base
adenine, the sugar ribose, and three phosphates
– ATP is sometimes called the “energy currency” of cells
© 2014 Pearson Education, Inc.
6.3 How Is Energy Transported Within Cells?
 ATP and electron carriers transport energy within
cells (continued)
– Energy is released in cells during glucose breakdown
and is used to combine the relatively low-energy
molecules adenosine diphosphate (ADP) and
phosphate (P) into ATP
– Energy is stored in the high-energy phosphate bonds
of ATP
– The formation of ATP is an endergonic reaction
© 2014 Pearson Education, Inc.
Figure 6-8 The interconversion of ADP and ATP
energy
ATP
ADP
phosphate
ATP synthesis: Energy is stored in ATP
energy
ATP
ADP
ATP breakdown: Energy is released
© 2014 Pearson Education, Inc.
phosphate
6.3 How Is Energy Transported Within Cells?
 ATP and electron carriers transport energy within
cells (continued)
– At sites in the cell where energy is needed, ATP is
broken down into ADP  P and its stored energy is
released
– This energy is then transferred to endergonic
reactions through coupling
– Unlike glycogen and fat, ATP stores energy very
briefly before being broken down
© 2014 Pearson Education, Inc.
6.3 How Is Energy Transported Within Cells?
 ATP and electron carriers transport energy within
cells (continued)
– ATP is not the only energy-carrier molecule in cells
– Energy can be transferred to electrons in glucose
metabolism and photosynthesis
– Electron carriers such as nicotinamide adenine
dinucleotide (NAD) and flavin adenine dinucleotide
(FAD) transport high-energy electrons
– Electron carriers donate their high-energy electrons to
other molecules, often leading to ATP synthesis
© 2014 Pearson Education, Inc.
6.3 How Is Energy Transported Within Cells?
 Coupled reactions link exergonic with endergonic
reactions
– In a coupled reaction, an exergonic reaction provides the
energy needed to drive an endergonic reaction
– Sunlight energy stored in glucose by plants is transferred
to other organisms by the exergonic breakdown of the
sugar and its use in endergonic processes such as protein
synthesis
– The two reactions may occur in different parts of the cell,
so energy-carrier molecules carry the energy from one to
the other
© 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc.
Animation: Coupled Reactions
Figure 6-9 Coupled reactions within living cells
high-energy
reactants
(glucose)
ATP
endergonic
(protein synthesis)
exergonic
(glucose breakdown)
low-energy
products
(CO2, H2O)
© 2014 Pearson Education, Inc.
high-energy
products
(protein)
ADP  Pi
low-energy
reactants
(amino acids)