Download Chapter 8 - Slothnet

Not happy with your grade?
Need help understanding the material?
The TLCC Has Free Tutoring
LECTURE PRESENTATIONS
For CAMPBELL BIOLOGY, NINTH EDITION
Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson
Chapter 8
An Introduction to Metabolism
Lectures by
Erin Barley
Kathleen Fitzpatrick
© 2011 Pearson Education, Inc.
Overview: The Energy of Life
• The living cell is a miniature chemical factory
where thousands of reactions occur
• The cell extracts energy and applies energy to
perform work
• Some organisms even convert energy to light,
as in bioluminescence
© 2011 Pearson Education, Inc.
Concept 8.1: An organism’s metabolism
transforms matter and energy, subject to the
laws of thermodynamics
• Metabolism all of an organism’s chemical
reactions
• an emergent property of life due to all the
interactions between molecules within the cell
© 2011 Pearson Education, Inc.
Organization of the Chemistry of Life into
Metabolic Pathways
• A metabolic pathway begins with a specific
molecule and ends with a product
• Each step is catalyzed by a specific enzyme
© 2011 Pearson Education, Inc.
• Catabolic pathways: release energy by
cutting big molecules apart
• Anabolic pathways: Add small molecules
together to make big ones, needs energy
– In many cases, that energy is ATP
– Plants use sunlight for energy as they make sugar
– Making proteins from amino acids is also anabolic
• Cellular respiration, the breakdown of glucose
in the presence of oxygen, is an example of a
pathway of catabolism
© 2011 Pearson Education, Inc.
Forms of Energy
• Energy is the capacity to cause change
• Energy exists in various forms, some of which can
perform work
• Bioenergetics is the study of how organisms
manage their energy resources
© 2011 Pearson Education, Inc.
• Kinetic energy is energy associated with motion
– Heat (thermal energy) is kinetic energy of randomly
moving of atoms or molecules
• Potential energy is energy that matter possesses
because of its location or structure
– Chemical energy is potential energy available
release in a chemical reaction
for
• Energy can be converted from one form to another
Animation: Energy Concepts
© 2011 Pearson Education, Inc.
Figure 8.2
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 isolated 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
© 2011 Pearson Education, Inc.
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
• Yes, biologist DO know about E=MC2
© 2011 Pearson Education, Inc.
(Ask later)
The Second Law of Thermodynamics
• Every energy transfer or transformation, wastes
some energy in an unusable form (often lost as heat)
• According to the second law of
thermodynamics
– Every energy transfer or transformation
increases the entropy (disorder) of the
universe (No transfer is 100% efficient)
© 2011 Pearson Education, Inc.
Figure 8.3a
Chemical
energy
(a) First law of thermodynamics
Figure 8.3b
Heat
(b) Second law of thermodynamics
• Living cells unavoidably convert organized
forms of energy (chemical) to heat
• Spontaneous processes: no energy used
– only happens if it increases the entropy of the
universe
© 2011 Pearson Education, Inc.
Biological Order and Disorder
• Cells: less ordered materials  ordered structures
• Organisms: ordered matter/energy  less ordered
• Energy FLOWS THROUGH an ecosystem
– Enters as light
– exits as heat
© 2011 Pearson Education, Inc.
• 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
Just like cells don’t violate thermodynamics
© 2011 Pearson Education, Inc.
Concept 8.2: The free-energy change of a
reaction tells us whether or not the reaction
occurs spontaneously
• Biologists 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
© 2011 Pearson Education, Inc.
Free-Energy Change, G
• A living system’s free energy is energy that
can do work when temperature and pressure
are uniform, as in a living cell
© 2011 Pearson Education, Inc.
• 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
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
Figure 8.5
• 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
Figure 8.5a
• 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
Figure 8.5b
(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
© 2011 Pearson Education, Inc.
Exergonic and Endergonic Reactions
exergonic reaction: releases release of free energy
– is spontaneous
endergonic reaction absorbs free energy
– Not spontaneous
© 2011 Pearson Education, Inc.
Equilibrium and Metabolism
• Closed systems eventually reach equilibrium
– Stop working
© 2011 Pearson Education, Inc.
Equilibrium and Metabolism
• metabolism is never at equilibrium
(Biology: not a closed system)
• Cells are always taking in food and energy
• catabolic pathway in a cell releases free energy
– Usually with several reactions in a row
© 2011 Pearson Education, Inc.
Concept 8.3: ATP powers cellular work
• A cell does three main kinds of work
– Chemical
– Transport
– Mechanical
• energy coupling (exergonic + endergonic)
– Exergonic: breaking energy rich molecules (usually ATP)
– use that energy to power endergonic reactions
• ATP is the main fuel to power the cell
© 2011 Pearson Education, Inc.
The Structure and Hydrolysis of ATP
• ATP (adenosine triphosphate) is the cell’s
energy shuttle
• ATP is composed of ribose (a sugar), adenine
(a nitrogenous base), and three phosphate
groups
© 2011 Pearson Education, Inc.
• The bonds between the phosphate groups
of ATP’s tail can be broken by hydrolysis
• Energy is released from ATP when the
terminal phosphate bond is broken
© 2011 Pearson Education, Inc.
How the Hydrolysis of ATP Performs Work
• All three types of cellular work (mechanical,
transport, and chemical) are powered by the
hydrolysis of ATP
• Breaking ATP is exergonic
– The energy released is used to drive endergonic
reactions
• Overall, the coupled reactions are exergonic
– More energy is released than is used
© 2011 Pearson Education, Inc.
Figure 8.9
(a) Glutamic acid
conversion
to glutamine
NH3
Glutamic
acid
(b) Conversion
reaction
coupled
with ATP
hydrolysis
NH2
Glu
Glu
GGlu = +3.4 kcal/mol
Glutamine
Ammonia
NH3
P
1
Glu
ATP
Glu
2
ADP
Glu
Phosphorylated
intermediate
Glutamic
acid
NH2
Glutamine
GGlu = +3.4 kcal/mol
(c) Free-energy
change for
coupled
reaction
NH3
Glu
GGlu = +3.4 kcal/mol
+ GATP = 7.3 kcal/mol
Net G = 3.9 kcal/mol
ATP
NH2
Glu
GATP = 7.3 kcal/mol
ADP
Pi
ADP
Pi
• ATP drives reactions that need energy
(endergonic) by transferring a phosphate group
to some other molecule, such as a reactant
– “Phosphorylation”
– The recipient molecule is now called a
phosphorylated intermediate
© 2011 Pearson Education, Inc.
The Regeneration of ATP
• ATP is a renewable resource
– ADP + P
• Uses energy from catabolic reactions
• Glucose is broken down to make ATP, which
powers other reactions
• Coal is burned in power plant to make
electricity, which powers lights, stove, etc.
• Difference: ATD and P can be used again
and again
© 2011 Pearson Education, Inc.
Figure 8.11
ATP
Energy from
catabolism (exergonic,
energy-releasing
processes)
ADP
H2O
Pi
Energy for cellular
work (endergonic,
energy-consuming
processes)
Concept 8.4: Enzymes speed up metabolic
reactions by lowering energy barriers
• Catalyst: speeds up chemical reaction without
being used up in reaction
• An enzyme is a catalytic protein
• Hydrolysis of sucrose by the enzyme sucrase
is an example of an enzyme-catalyzed
reaction
© 2011 Pearson Education, Inc.
The Activation Energy Barrier
• chemical reaction: breaking and making bonds
• activation energy (EA) The initial energy
needed to start a chemical reaction
• Activation energy is often supplied in the form
of thermal energy that the reactant molecules
absorb from their surroundings
© 2011 Pearson Education, Inc.
Figure 8.12
A
B
C
D
Free energy
Transition state
A
B
C
D
EA
Reactants
A
B
G  O
C
D
Products
Progress of the reaction
How Enzymes Lower the EA Barrier
• Enzymes catalyze reactions (speed them up)
by lowering the activation energy
• Enzymes do not affect the change in free
energy (∆G); instead, they speed up reactions
that would occur eventually
Animation: How Enzymes
© 2011 Pearson Education, Inc.
Substrate Specificity of Enzymes
• Substrate: reactant the enzyme works on
• The enzyme binds to its substrate, forming an
enzyme-substrate complex
• active site: spot on enzyme where substrate
binds
• Induced fit: change in enzyme shape after
substrate binding
© 2011 Pearson Education, Inc.
Catalysis in the Enzyme’s Active Site
• substrate binds to the active site of the enzyme
Ways enzyme lowers
activation energy
1. Orienting substrates
correctly
2. Straining substrate
bonds
3. Providing a favorable
microenvironment
4. Covalently bonding to
the substrate
© 2011 Pearson Education, Inc.
Conditions that affect Enzyme Activity
• An enzyme’s activity can be affected by
– General environmental factors, such as
temperature and pH
• If you denature it, you stop the reactions
• If you slow down the collisions, you reduce the
reactions
– Chemicals that specifically influence the
enzyme
• Inhibitor molecules
© 2011 Pearson Education, Inc.
Effects of Temperature and pH
• Each enzyme has an optimal temperature in
which it can function
• Each enzyme has an optimal pH in which it can
function
• Optimal conditions favor the most active shape
for the enzyme molecule
© 2011 Pearson Education, Inc.
Figure 8.16
Rate of reaction
Optimal temperature for
Optimal temperature for
typical human enzyme (37°C) enzyme of thermophilic
(heat-tolerant)
bacteria (77°C)
60
80
Temperature (°C)
(a) Optimal temperature for two enzymes
0
20
40
Rate of reaction
Optimal pH for pepsin
(stomach
enzyme)
0
5
pH
(b) Optimal pH for two enzymes
1
2
3
4
120
100
Optimal pH for trypsin
(intestinal
enzyme)
6
7
8
9
10
Cofactors
• Cofactors: non-protein enzyme helpers
– Can be inorganic (e.g. a metal ion) or organic
• An organic cofactor is called a coenzyme
• Coenzymes include vitamins
© 2011 Pearson Education, Inc.
Enzyme Inhibitors
• Competitive inhibitors: bind to the active site
of an enzyme, competing with the substrate
• Noncompetitive inhibitors bind to another
part of an enzyme, causing the enzyme to
change shape and making the active site less
effective (“allosteric inhibitor”)
• Examples of inhibitors include toxins, poisons,
pesticides, and antibiotics
© 2011 Pearson Education, Inc.
Figure 8.17
(a) Normal binding
(b) Competitive inhibition
(c) Noncompetitive
inhibition
Substrate
Active
site
Competitive
inhibitor
Enzyme
Noncompetitive
inhibitor
The Evolution of Enzymes
• Enzymes are proteins encoded by genes
• Changes (mutations) in genes lead to changes
in amino acid composition of an enzyme
• Altered amino acids in enzymes may alter their
substrate specificity
• Under new environmental conditions a novel
form of an enzyme might be favored
© 2011 Pearson Education, Inc.
Figure 8.18
Two changed amino acids were
found near the active site.
Two changed amino acids
were found in the active site.
Active site
Two changed amino acids
were found on the surface.
Concept 8.5: Regulation of enzyme activity
helps control metabolism
• metabolic pathways must be tightly regulated
• Two methods a cell uses
1. Starting or stopping production of an enzyme
•
A cell does this by switching on or off the genes with
instructions to make that specific enzyme
2. regulating the activity of existing enzymes
© 2011 Pearson Education, Inc.
Allosteric Regulation of Enzymes
• Allosteric regulation:
regulatory molecule
binds to protein at one
site and affects the
protein’s function at
another site
– Often by changing shape
of enzyme
• may either inhibit or
stimulate an enzyme’s
activity
© 2011 Pearson Education, Inc.
Allosteric Activation and Inhibition
• Most allosterically regulated enzymes are
made from several polypeptide subunits
– have active and inactive forms
– Binding to activator molecule stabilizes the active
form of the enzyme
– Binding to an inhibitor molecule stabilizes the
inactive form of the enzyme
© 2011 Pearson Education, Inc.
• Cooperativity: allosteric regulation that
amplifies enzyme activity
• One substrate molecule makes the other active
sites work better
• allosteric because binding affects a different
active site
© 2011 Pearson Education, Inc.
Cooperativity: not just enzymes
• Carrying an oxygen makes hemoglobin
better at picking up additional oxygen
Identification of Allosteric Regulators
• Allosteric regulators are attractive drug
candidates for enzyme regulation because of
their specificity
• Inhibition of proteolytic enzymes called
caspases may help management of
inappropriate inflammatory responses
© 2011 Pearson Education, Inc.
Feedback Inhibition
• In feedback inhibition,
the end product of a
metabolic pathway shuts
down the pathway
• Feedback inhibition
prevents a cell from
wasting chemical
resources by
synthesizing more
product than is needed
© 2011 Pearson Education, Inc.
Feedback Inhibition: also in gene expression
The Lac Operon
If there’s no lactose to
digest, expression is
inhibited for the
genes that make
lactase-digesting
enzymes
Lactose inhibits the inhibitor!!!
Specific Localization of Enzymes Within
the Cell
• metabolic pathways work better because of
structures within the cell
– Some enzymes act as structural components of
membranes
– In eukaryotic cells, some enzymes reside in specific
organelles; for example, enzymes for cellular
respiration are located in mitochondria
© 2011 Pearson Education, Inc.
Enzyme Localization in mitochondria
– enzymes for cellular respiration are located in
mitochondria
© 2011 Pearson Education, Inc.
Concept Quiz
Why are high fevers dangerous and
sometimes life-threatening?
A. Molecules move faster at higher temperatures.
B. Enzymes may change shape at high
temperatures.
C. Invading microbes survive better and
reproduce faster at high temperatures.
Concept Quiz
Where a substrate binds to an enzyme is
known as the
A. Active site
B. Activation energy
C. Energy transfer site
Enzymes: Effect of Temperature
Enzymes: Effect of Temperature
Enzymes: effect of pH
Enzymes: Effect of Concentration
Not happy with your grade?
Need help understanding the material?
The TLCC Has Free Tutoring