Transcript Understanding Our Environment

Energy and Metabolism
Chapter 8
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Outline
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Energy Flow in Living Things
Laws of Thermodynamics
Free Energy
Activation Energy
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Energy Flow in Living Things
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Energy - Capacity to perform work.
 Kinetic Energy - Energy of motion.
 Potential Energy - Stored energy due to an
object’s relative position.
Thermodynamics - Study of energy.
 Kilocalorie (1,000 calories)
- Calorie - Heat required to raise
temperature of one gram of water one
degree Celsius.
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Energy Flow in Living Things
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Oxidation-Reduction
 During a chemical reaction, the energy
stored in chemical bonds may transfer to
new bonds.
- Oxidation - Atom or molecule loses an
electron.
- Reduction - Atom or molecule gains an
electron.
 Always take place together.
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Laws of Thermodynamics
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First Law - Energy is neither created nor
destroyed; it can only change from one form
to another.
 Total amount of energy in the universe
remains constant.
- During energy conversion, some energy
dissipates into the environment as heat.
 Energy flows one-way from the sun
through the environment.
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Laws of Thermodynamics
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Second Law - Entropy in the universe is
continuously increasing.
 Entropy increases continuously.
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Free Energy
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Free Energy of a molecule is the amount of
energy actually available to break and
subsequently form other chemical bonds.
- the energy available to do work.
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Free Energy
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Endergonic Reaction - Requires energy input.
Exergonic Reaction - Occurs spontaneously
and releases excess free energy.
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Activation Energy
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Activation Energy is the energy required to
destabilize existing chemical bonds and
initiate a chemical reaction.
- Most reactions require energy to get
started
- Catalysis - Process of lowering
necessary activation energy.
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Activation Energy and Catalysis
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Enzymes
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Enzymes carry out most catalysis in living
organisms.
 Unique three-dimensional shape of an
enzyme enables it to stabilize a temporary
association between substrates.
- Lowers activation energy necessary for
new bonds to form.
(stop here for now!)
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Enzymes (continued from last week)
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How Enzymes Work
 Most enzymes are globular proteins with
one or more active sites for substrates to
bind.
- Substrate binding induces enzyme to
adjust its shaped for an induced fit.
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Enzyme Catalytic Cycle
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Enzymes
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Enzyme Forms
 Multienzyme Complexes
- Enzymes catalyzing different steps of a
sequence are loosely associated with
one another.
 Increase catalytic efficiency.
Not all Biological Catalysts are Proteins.
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Factors Affecting Enzyme Activity
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Temperature
 Rate increase with temperature up to
temperature optimum.
pH
 Changing concentration of hydrogen ions
shifts the balance between positively and
negatively charged amino acid residues.
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Factors Affecting Enzyme Activity
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Inhibitors and Activators
 Inhibitors - Decrease enzyme activity.
- Competitive - Compete with substrate for
same binding site.
- Noncompetitive - Bind to enzyme in
other location, altering shape.
 Allosteric Site
 Activators - Bind to allosteric sites and
keep enzymes in active configurations.
- Increase enzyme activity.
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Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies
Factors Affecting Enzyme Activity
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Enzyme Cofactors - Enzyme function
assisted by additional chemical components.
 Coenzyme - Nonprotein organic molecule
serves as cofactor.
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ATP
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Adenosine triphosphate (energy currency)
 Composed of:
- Five-carbon sugar (ribose)
- Adenine
- Triphosphate group
 Energy Storage
- Phosphate groups are highly negatively
charged.
 Unstable bonds easily broken.
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ATP
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Cells use ATP to drive endergonic reactions.
 Instability makes ATP ideal for short-term
energy source, but a poor candidate for
long-term energy storage.
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Biochemical Pathways
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Metabolism - Total of all chemical reactions
carried out by an organism.
 Anabolism - Expend energy to make
chemical bonds.
 Catabolism - Harvest energy when
chemical bonds are broken.
Biochemical Pathways - Products of one
reaction becomes substrate for the next.
 Regulated by feedback inhibition.
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Biochemical Pathways
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Evolution of Metabolism
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Degradation
Glycolysis
Anaerobic Photosynthesis
Nitrogen Fixation
Oxygen-Forming Photosynthesis
Aerobic Photosynthesis
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Review
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Energy Flow in Living Things
Laws of Thermodynamics
Free Energy
Activation Energy
Enzymes
Factors Affecting Enzyme Activity
ATP
Biochemical Pathways
Evolution of Metabolism
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