Lecture PowerPoint to accompany
Inquiry into Life
Twelfth Edition
Sylvia S. Mader
Chapter 6
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
6.1 Cells and the Flow of
Energy
6.1 Cells and the Flow of
Energy
• Energy is the ability to do work or bring
about change.
6.1 Cells and the Flow of
Energy
• Energy is the ability to do work or bring
about change.
• Forms of Energy
6.1 Cells and the Flow of
Energy
• Energy is the ability to do work or bring
about change.
• Forms of Energy
– Kinetic energy is the energy of motion.
6.1 Cells and the Flow of
Energy
• Energy is the ability to do work or bring
about change.
• Forms of Energy
– Kinetic energy is the energy of motion.
– Potential energy is stored energy.
Flow of Energy
6.1 Cells and the Flow of
Energy
• Two Laws of Thermodynamics
– Energy cannot be created or destroyed,
but it can be changed from one form to
another.
– Energy cannot be changed from one form
to another without a loss of usable energy.
6.1 Cells and the Flow of
Energy
6.1 Cells and the Flow of
Energy
• Cells and Entropy
– Entropy refers to the relative amount of
disorganization.
6.1 Cells and the Flow of
Energy
• Cells and Entropy
– Entropy refers to the relative amount of
disorganization.
– Energy transformations in cells increase
the amount of entropy.
6.1 Cells and the Flow of
Energy
• Processes in living
organisms require
an input of energy
that is ultimately lost
as heat.
6.2 Metabolic Reactions and
Energy Transformations
6.2 Metabolic Reactions and
Energy Transformations
• Metabolism is the sum of all the chemical
reactions that occur in a cell.
6.2 Metabolic Reactions and
Energy Transformations
• Metabolism is the sum of all the chemical
reactions that occur in a cell.
A+B
(reactants)
C+D
(products)
6.2 Metabolic Reactions and
Energy Transformations
• Free energy (∆G) is the amount of energy
available.
6.2 Metabolic Reactions and
Energy Transformations
• Free energy (∆G) is the amount of energy
available.
– Exergonic reactions are ones where energy is
released (∆G is negative)
6.2 Metabolic Reactions and
Energy Transformations
• Free energy (∆G) is the amount of energy
available.
– Exergonic reactions are ones where energy is
released (∆G is negative)
– Endergonic reactions require an input of
energy. (∆G is positive)
6.2 Metabolic Reactions and
Energy Transformations
• ATP: Energy for Cells
– ATP stands for adenosine triphosphate, the
common energy currency for cells.
6.2 Metabolic Reactions and
Energy Transformations
• ATP: Energy for Cells
– ATP stands for adenosine triphosphate, the
common energy currency for cells.
– ATP is generated from ADP (adenosine
diphosphate) + an inorganic phosphate
molecule ( P )
The ATP Cycle
6.2 Metabolic Reactions and
Energy Transformations
• Structure of ATP
– ATP is a nucleotide that is composed of:
• Adenine (a nitrogen-containing base)
• Ribose (a 5-carbon sugar)
• Three phosphate groups
6.2 Metabolic Reactions and
Energy Transformations
• Structure of ATP
– ATP is a “high energy” compound because
a phosphate group can easily be removed.
6.2 Metabolic Reactions and
Energy Transformations
• Coupled Reactions
– The energy released by an exergonic reaction is
used to drive an endergonic reaction.
Coupled Reactions
6.3 Metabolic Pathways and
Enzymes
• Metabolic pathways are a series of
linked reactions.
– These begin with a specific reactant and
produce an end product
6.3 Metabolic Pathways and
Enzymes
• Enzymes are usually proteins that
function to speed a chemical reaction.
– Enzymes serve as catalysts
A Metabolic Pathway
6.3 Metabolic Pathways and
Enzymes
• The Energy of Activation (Ea) is the
energy that must be added to cause
molecules to react with one another.
Energy of Activation
6.3 Metabolic Pathways and
Enzymes
• How Enzymes Function
– Enzyme binds substrate to form a complex
– E + S  ES  E + P
Enzymatic Action
6.3 Metabolic Pathways and
Enzymes
• How Enzymes Function
– Enzyme binds substrate to form a complex
– E + S  ES  E + P
– Induced fit model
• Substrate and active site shapes don’t match exactly
• Active site is induced to undergo a slight change in
shape to accommodate substrate binding
Induced Fit Model
6.3 Metabolic Pathways and
Enzymes
• Factors Affecting Enzymatic Speed
– Substrate Concentration
– Temperature and pH
– Enzyme Activation
– Enzyme Inhibition
– Enzyme Cofactors
6.3 Metabolic Pathways and
Enzymes
• Substrate Concentration
• Enzyme activity increases as substrate
concentration increases because there are
more collisions between substrate and enzyme
• Maximum rate is achieved when all active sites
of an enzyme are filled continuously with
substrate
Metabolic Pathways and
Enzymes
• Temperature
– Enzyme activity increase as temperature rises
– Higher temperatures cause more effective
collisions between enzymes and substrates
– High temperatures may denature an enzyme,
inhibiting its ability to bind to substrates
The Effect of Temperature on
the Rate of Reaction
Metabolic Pathways and
Enzymes
• pH
• Each enzyme has an optimal pH
• Enzyme structure is pH dependent
• Extremes of pH can denature an enzyme by
altering its structure
Effect of pH on the Rate of
Reaction
Metabolic Pathways and
Enzymes
• Enzyme Activation
– Cell regulates metabolism by regulating which enzymes are
active
– Genes producing enzymes can be turned on or off to
regulate enzyme concentration
– In some cases a signaling molecule is used to activate an
enzyme
Metabolic Pathways and
Enzymes
• Enzyme Inhibition
– Occurs when enzyme cannot bind its substrate
– Activity of cell enzymes is regulated by feedback inhibition
– Ex: when product is abundant it binds to the enzyme’s active
site and blocks further production
– When product is used up, it is removed from the active site
– In a more complex type of inhibition, product binds to a site
other than the active site, which changes the shape of the
active site
– Poisons are often enzyme inhibitors
Feedback Inhibition
Metabolic Pathways and
Enzymes
• Enzyme Cofactors
– Molecules which help enzyme function
– Copper and zinc are examples of inorganic
cofactors
– Organic non-protein cofactors are called
coenzymes
• Vitamins are often components of coenzymes
6.4 Oxidation-Reduction and
the Flow of Energy
• Oxidation-Reduction
– Oxidation is the loss of electrons
– Reduction is the gaining of electrons
– Ex: when oxygen combines with a metal like Mg,
oxygen receives electrons (becomes negatively
charged) and Mg loses electrons (becomes
positively charged)
• We say Mg has become oxidized, and oxygen
is reduced (has a negative charge) when MgO
forms
6.4 Oxidation-Reduction and
the Flow of Energy
• Oxidation-Reduction
– The term oxidation is used even when
oxygen is not involved
• Ex: Na+ + Cl-  NaCl in which sodium is
oxidized and chloride is reduced
– This also applies to covalent reactions
involving hydrogen atoms
– Oxidation is the loss of hydrogen and
reduction is the gain of hydrogen atoms
6.4 Oxidation-Reduction and
the Flow of Energy.
• Photosynthesis
– energy + 6CO2+6H2O C6H12O6 + 6O2
– Hydrogen atoms are transferred from water to carbon
dioxide and glucose is formed
– Energy is required and this comes in the form of light
energy from the sun
– Chloroplasts convert solar energy to ATP which is
then used along with hydrogen to reduce carbon
dioxide to glucose
Oxidation-reduction and the flow
of energy cont’d.
• Cell Respiration
–
–
–
–
C6H12O6 + 6O2 6CO2 + 6H2O + energy
Glucose is oxidized (lost hydrogen atoms)
Oxygen is reduced to form water
Complete oxidation of a mole of glucose produces
686 kcal of energy
– This energy is used to form ATP
– The oxidation of glucose to form ATP is done is a
series of small steps to increase efficiency
6.4 Oxidation-Reduction and
the Flow of Energy.
• Organelles and the flow of energy
– Cycling of molecules between chloroplasts and
mitochondria allows energy to flow from sun to all
living things
– Chloroplasts use light energy from the sun to make
carbohydrates
– Mitochondria break down carbohydrates to form ATP
– Cell respiration produces carbon dioxide and water
which are used in photosynthesis
Relationship of Chloroplasts to
Mitochondria