Transcript BIG IDEA II Biological systems utilize free energy and molecular

BIG IDEA II
Biological systems utilize free energy and molecular building blocks
to grow, to reproduce and to maintain dynamic homeostasis.
Enduring Understanding 2.A
Growth, reproduction and maintenance of the organization
of living systems require free energy and matter.
Essential Knowledge 2.A.1
All living systems require a constant input of free energy.
Essential Knowledge 2.A.1: All living systems
require a constant input of free energy.
• Learning Objectives:
– (2.1) The student is able to explain how biological systems
use free energy based on empirical data that all organisms
require constant energy input to maintain organization, to
grow and to reproduce.
– (2.2) The student is able to justify a scientific claim that free
energy is required for living systems to maintain organization,
to grow or to reproduce, but that multiple strategies exist in
different living systems.
– (2.3) The student is able to predict how changes in free
energy availability affect organisms, populations and
ecosystems.
Fig. 9-2
Light
energy
ECOSYSTEM
Photosynthesis
in chloroplasts
CO2 + H2O
Organic
+O
molecules 2
Cellular respiration
in mitochondria
ATP
ATP powers most cellular work
Heat
energy
Life Requires a Highly Ordered System
• The living cell is a chemical factory in miniature, where
thousands of reactions occur within a microscopic space.
– Order is maintained by constant free energy input into the system.
– Loss of order or free energy flow results in death.
– Increased disorder and entropy are offset by biological processes
that maintain or increase order.
• The concepts of metabolism help us to understand how matter
and energy flow during life’s processes and how that flow is
regulated in living systems.
Metabolism
• Metabolism is the totality of an organism’s chemical reactions:
– An organism’s metabolism transforms matter and energy,
subject to the laws of thermodynamics.
• Metabolism is an emergent property of life that arises from
interactions between molecules within the cell.
• A metabolic pathway begins with a specific molecule and ends
with a product, whereby each step is catalyzed by a specific
enzyme.
• Bioenergetics is the study of how organisms manage their
energy resources.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Overview: A Metabolic Pathway
Enzyme 1
Enzyme 2
B
A
Reaction 1
Starting
molecule
Enzyme 3
C
Reaction 2
D
Reaction 3
Product
Catabolism and Anabolism
• Catabolic pathways release energy by breaking
down complex molecules into simpler
compounds:
– Cellular respiration, the breakdown of glucose in the
presence of oxygen, is an example of a pathway of
catabolism.
• Anabolic pathways consume energy to build
complex molecules from simpler ones:
– The synthesis of protein from amino acids is an
example of anabolism.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Forms of Energy
• Energy is the capacity to cause change.
• Energy exists in various forms, some of which can perform work:
– Kinetic energy is energy associated with motion.
– Heat (thermal energy) is kinetic energy associated with random
movement of atoms or molecules.
– Potential energy is energy that matter possesses because of its
location or structure.
– Chemical energy is potential energy available for release in a
chemical reaction.
• Energy cannot be created or destroyed, but can be converted
from one form to another.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
A diver has more potential
energy on the platform
than in the water.
Climbing up converts the kinetic
energy of muscle movement
to potential energy.
Diving converts
potential energy to
kinetic energy.
A diver has less potential
energy in the water
than on the platform.
The Laws of Energy Transformation
• Thermodynamics is the study of energy
transformations.
• A closed system, such as that approximated by
liquid in a thermos, is isolated from its
surroundings.
• In an open system, energy and matter can be
transferred between the system and its
surroundings.
• Organisms are open systems.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
The First Law of Thermodynamics
• 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 called the principle of
conservation of energy.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
The Second Law of Thermodynamics
• During every energy transfer or transformation,
some energy is unusable, and is often lost as heat.
• According to the second law of thermodynamics:
– Every energy transfer or transformation increases the
entropy (disorder) of the universe.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Heat
Chemical
energy
(a) First law of thermodynamics
CO2
+
H2O
(b) Second law of thermodynamics
Biological Order and Disorder
• Cells create ordered structures from less ordered
materials.
• Organisms also replace ordered forms of matter and
energy with less ordered forms.
• Energy flows into an ecosystem in the form of light and
exits in the form of heat.
• The evolution of more complex organisms does not
violate the second law of thermodynamics.
• Entropy (disorder) may decrease in an organism, but the
universe’s total entropy increases.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Free-Energy Change, G
• The free-energy change of a reaction tells us
whether or not the reaction occurs
spontaneously.
• Biologists often want to know which reactions
occur spontaneously and which require input of
energy.
• To do so, they need to determine energy
changes that occur in chemical reactions.
• A living system’s free energy is energy that can
do work when temperature and pressure are
uniform, as in a living cell.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Free-Energy Change, G
• The change in free energy (∆G) during a process
is related to the change in enthalpy, or change
in total energy (∆H), change in entropy (∆S), and
temperature in Kelvin (T):
∆G = ∆H – T∆S
• Only processes with a negative ∆G are
spontaneous.
• Spontaneous processes can be harnessed to
perform work.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Free Energy, Stability, and Equilibrium
• Free energy is a measure of a system’s instability, its
tendency to change to a more stable state.
• During a spontaneous change, free energy
decreases and the stability of a system increases.
• Equilibrium is a state of maximum stability.
• A process is spontaneous and can perform work
only when it is moving toward equilibrium.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
• More free energy (higher G)
• Less stable
• Greater work capacity
In a spontaneous change
• The free energy of the system
decreases (∆G < 0)
• The system becomes more
stable
• The released free energy can
be harnessed to do work
• Less free energy (lower G)
• More stable
• Less work capacity
(a) Gravitational motion
(b) Diffusion
(c) Chemical reaction
Free Energy and Metabolism
• The concept of free energy can be applied to
the chemistry of life’s processes:
– An exergonic reaction proceeds with a net release
of free energy and is spontaneous (∆G is negative).
– An endergonic reaction absorbs free energy from its
surroundings and is nonspontaneous (∆G is
positive).
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Reactants
Free energy
Amount of
energy
released
(∆G < 0)
Energy
Products
Progress of the reaction
(a) Exergonic reaction: energy released
Free energy
Products
Amount of
energy
required
(∆G > 0)
Energy
Reactants
Progress of the reaction
(b) Endergonic reaction: energy required
∆G < 0
∆G = 0
(a) An isolated hydroelectric system
(b) An open hydroelectric
system
∆G < 0
∆G < 0
∆G < 0
∆G < 0
(c) A multistep open hydroelectric system
ATP & Energy Coupling
H2O
Energetically favorable exergonic reactions, such as ATPADP, that have
negative change in free energy can be used to maintain or increase order
in a system by being coupled with reactions that have a positive free
energy exchange.
P
P
P
Adenosine triphosphate (ATP)
H2O
Pi
+
Inorganic phosphate
P
P
+
Adenosine diphosphate (ADP)
Energy
NH2
Glu
Glutamic
acid
NH3
+
Glu
∆G = +3.4 kcal/mol
Glutamine
Ammonia
(a) Endergonic reaction
1 ATP phosphorylates
glutamic acid,
making the amino
acid less stable.
P
+
Glu
ATP
Glu
+ ADP
NH2
2 Ammonia displaces
the phosphate group,
forming glutamine.
P
Glu
+
NH3
Glu
+ Pi
(b) Coupled with ATP hydrolysis, an exergonic reaction
(c) Overall free-energy change
Membrane protein
P
Solute
Pi
Solute transported
(a) Transport work: ATP phosphorylates
transport proteins
ADP
+
ATP
Pi
Vesicle
Cytoskeletal track
ATP
Motor protein
Protein moved
(b) Mechanical work: ATP binds noncovalently
to motor proteins, then is hydrolyzed
Energy Related Pathways in Biological
Systems
• Energy-related pathways in biological systems
are sequential and may be entered at multiple
points in the pathway:
– Glycolysis
– Krebs cycle
– Calvin cycle
– Fermentation
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Use of Free Energy
• Organisms use free energy to maintain
organization, grow and reproduce. Illustrative
Examples include:
– Strategies to regulate body temperature
– Strategies for reproduction & rearing of offspring
– Metabolic rate and size
– Excess acquired free energy
– Insufficient acquired free energy
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Bioenergetics of Animals
• Animals use the chemical energy in food to sustain form
and function.
• All organisms require chemical energy for growth, repair,
physiological processes, regulation, and reproduction.
• The flow of energy through an animal, its bioenergetics,
ultimately limits the animal’s behavior, growth, and
reproduction – which determines how much food it needs.
• Studying an animal’s bioenergetics tells us a great deal
about the animal’s adaptations.
Bioenergetics of an Animal
Quantifying Energy Use
• An animal’s metabolic rate is the amount of energy it uses in a
unit of time.
• An animal’s metabolic rate is closely related to its bioenergetic
strategy – which determines nutritional needs and is related to
an animal’s size, activity, and environment:
– The basal metabolic rate (BMR) is the metabolic rate of a non-growing,
unstressed endotherm at rest with an empty stomach.
– The standard metabolic rate (SMR) is the metabolic rate of a fasting, nonstressed ectotherm at rest at a particular temperature.
– For both endotherms and ectotherms, size and activity has a large effect
on metabolic rate.
Organisms use various strategies to
regulate body temperature and
metabolism.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Elevated Floral Temperature in Some Plant Species
Different organisms use various
reproductive strategies in response to
energy availability.
Seasonal Reproduction in Plants
Metabolic Rate and Size of Organisms
• There is a relationship between metabolic rate per
unit body mass and the size of multicellular
organisms – generally, the smaller the organism,
the higher the metabolic rate.
• Larger animals have more body mass and
therefore require more chemical energy.
• Remarkably, the relationship between overall
metabolic rate and body mass is constant across
a wide range of sizes and forms.
Metabolic Rate and Size of Organisms
Changes in Free Energy Availability
• Changes in free energy availability can result in
changes in population size and disruption to an
ecosystem.
• Change in the producer level can affect the
number and size of other trophic levels.
• Change in energy resource levels such as
sunlight can affect the number and size of the
trophic levels.
Changes in Free Energy Availability