Ground Rules of Metabolism. Catalase is an enzyme that helps the body break down toxic substances...
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CHAPTER 6Ground Rules of Metabolism
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IMPACTS, ISSUES: ALCOHOL, ENZYMES, AND YOUR LIVER
Catalase is an enzyme that helps the body break down toxic substances in alcoholic drinks
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IMPACTS, ISSUES: ALCOHOL, ENZYMES, AND YOUR LIVER
The liver plays a central role in alcohol metabolism
Consumption of too much alcohol, as in binge drinking, can lead to alcoholic hepatitis or alcoholic cirrhosis
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WHAT IS ENERGY? Capacity to do work
Forms of energyPotential energyKinetic energyChemical energy
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FIRST LAW OF THERMODYNAMICS The total amount of energy in the
universe remains constant
Energy can undergo conversions from one form to another, but it cannot be created or destroyed
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ENERGY LOSTWith each conversion, there is a one-way flow of a bit of energy back to the environment. Nutrients cycle between producers and consumers.
ENERGY GAINEDSunlight energy reaches environments on Earth. Producers of nearly all ecosystems secure someand convert it to stored forms of energy. They and all other organisms convert stored energy to forms that can drive cellular work.
ENERGY LOSTEnergy continually flows from the sun.
producers
consumers
NUTRIENTCYCLING
Fig. 6-4, p.74
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SECOND LAW OF THERMODYNAMICS
No energy conversion is ever 100 percent
efficient
The total amount of energy is flowing from
high-energy forms to forms lower in energy
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BOZEMAN VIDEO—GIBBS FREE ENERGYhttp://
www.youtube.com/watch?v=DPjMPeU5OeM
http://www.youtube.com/watch?v=JBmykor-2kU
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ENTROPY Measure of degree of disorder in a
system
The world of life can resist the flow toward maximum entropy only because it is resupplied with energy from the sun
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PARTICIPANTS IN METABOLIC REACTIONS
Energy carriers
Enzymes
Cofactors
Transport proteins
Reactants
Intermediates
Products
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THE ROLE OF ATP
Cells “earn” ATP in exergonic reactions Cells “spend” ATP in endergonic reactions
base
sugar
three phosphate
groups
Fig. 6-6a, p.96
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ENDERGONIC REACTIONS Energy input
required
Product has more
energy than starting
substances
glucose, a high energy product
ENERGY IN
low energy starting substances
6
+ 6O2
6
66
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EXERGONIC REACTIONS Energy is
released Products have
less energy than starting substance
glucose, a high energy starting substance
+ 6O2
6 6
low energy products
ENERGY OUT
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reactions that
release energy
reactions that
require energy
cellular work
(e.g., synthesis,breakdown, or rearrangement of substances;contraction ofmuscle cells; active transportacross a cellmembrane)
ATP
ADP + Pi
ATP
Fig. 6-7a, p.75
ATP/ADP Cycle
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ENZYME STRUCTURE AND FUNCTION
Enzymes are catalytic molecules
They speed the rate at which reactions approach equilibrium
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FOUR FEATURES OF ENZYMES
1) Enzymes do not make anything happen that could not happen on its own. They just make it happen much faster.
2) Reactions do not alter or use up enzyme molecules.
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FOUR FEATURES OF ENZYMES
3) The same enzyme usually works for both the forward and reverse reactions.
4) Each type of enzyme recognizes and binds to only certain substrates.
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BOZEMAN VIDEO--ENZYMEShttp://www.youtube.com/watch?v=ok9esggzN18
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ACTIVATION ENERGY
For a reaction to occur, an energy barrier must be surmounted
Enzymes make the energy barrier smaller
activation energywithout enzyme
activation energywith enzyme
energyreleasedby the
reaction
products
starting substance
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Fig. 6-10b, p.97
Hydrogen peroxide (H2O2) enters a catalase. It is the substrate for a reaction aided by an iron molecule in a heme group (red).
A hydrogen of the peroxide is attracted to histidine, an amino acid projecting into the cavity. One oxygen binds the iron.
This binding destabilizes the peroxide bond which breaks. Water (H2O) forms. In a later reaction, another H2O2
will pull the oxygen from iron, which will then be free to act again.
How Catalase Works
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INDUCED-FIT MODEL
Substrate molecules are brought together Substrates are oriented in ways that favor
reaction Active sites may promote acid-base
reactions Active sites may shut out water
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2 TYPES OF INHIBITORS: Competitive—competes with the
substrate for the ACTIVE SITE Noncompetitive (AKA allosteric)—
inhibitor bonds to allosteric site (away from active site)
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ALLOSTERIC INHIBITION
allosteric inhibitor
allosteric binding site vacant; active site can bind substrate
active site altered, can’t bind substrate
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ALLOSTERIC ACTIVATION
allosteric activator
vacantallosteric binding site
active site altered, can bind substrate
active site cannot bind substrate
enzyme active site
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COOPERATIVITY When a substrate binds to the active
site of one of the enzyme’s subunits causing the same effect on all of the enzyme’s subunits
This can “prime” an enzyme to start accepting more and more substrate
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FEEDBACK INHIBITION
enzyme 2 enzyme 3 enzyme 4 enzyme 5
enzyme 1
SUBSTRATE
END PRODUCT (tryptopha
n)
A cellular change, caused by a specific activity, shuts down the activity that brought it about
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2 TYPES OF FEEDBACK: Positive---Ex: contractions & childbirth
Negative—AKA antagonisticEx: fever
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FACTORS INFLUENCING ENZYME ACTIVITY
Temperature
pH
Salt concentration
Allosteric regulators
Coenzymes and cofactors
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EFFECT OF TEMPERATURE Small increase in
temperature increases molecular collisions, reaction rates
High temperatures disrupt bonds and destroy the shape of active site
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Fig. 6-13, p.81
Effect of Temperature
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EFFECT OF PH
Fig. 6-14a, p.81
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ENZYME HELPERS Cofactors
Coenzymes NAD+, NADP+, FAD Accept electrons and hydrogen ions; transfer
them within cell Derived from vitamins
Metal ions Ferrous iron in cytochromes
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METABOLIC PATHWAYS
Defined as enzyme-mediated sequences of reactions in cellsBiosynthetic (anabolic) –
ex: photosynthesisDegradative (catabolic)
– ex: aerobic
respiration
ENERGY IN ENERGY IN
organiccompounds,
oxygen
photosynthesis
aerobic respiration
ENERGY OUT
carbondioxide,
water
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REDOX REACTIONS
Cells release energy efficiently by electron transfers, or oxidation-reduction reactions (“redox” reactions)
One molecule gives up electrons (is oxidized) and another gains them (is reduced)
Hydrogen atoms are commonly released at the same time, thus becoming H+
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ELECTRON TRANSFER CHAINS Arrangement of enzymes, coenzymes,
at cell membrane
As one molecule is oxidized, next is
reduced
Function in aerobic respiration and
photosynthesis
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BIOLUMINESCENCE An outcome of enzyme-mediated
reactions that release energy as fluorescent light
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Fig. 6-19, p.103
Bioluminescent Bacteria
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OTHER REVIEW VIDEOS:http://www.youtube.com/watch?v=NzxgpsW_rJI