intro to metabolism campbell chapter 8
TRANSCRIPT
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Intro to MetabolismCampbell Chapter 8
http://www.gifs.nethttp://ag.ansc.purdue.edu/sheep/ansc442/Semprojs/2003/spiderlamb/eatsheep.gif
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• Metabolism is the sum of an organism’s chemical reactions
• Metabolism is an emergent property of life that arises from interactions between molecules within the cellhttp://www.encognitive.com/images/metabolic-pathways.png
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A metabolic pathway begins with a specific molecule and ends with a product
• Each step is catalyzed by a specific enzyme
BIOCHEMICAL PATHWAYVIDEO
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ENZYMES THAT WORK TOGETHER IN A PATHWAY CAN BE
Soluble with free floating intermediates
Covalently bound incomplex
Attached toa membranein sequenceBiochemistry Lehninger
Concentrated in specific location
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CATABOLIC PATHWAY (CATABOLISM)Release of energy by the breakdown of complex molecules to simpler compoundsEX: digestive enzymes break down food
ANABOLIC PATHWAY (ANABOLISM)consumes energy to build complicated molecules from simpler onesEX: linking amino acids to form proteins
http://www.sciencelearn.org.nz/var/sciencelearn/storage/images/contexts/nanoscience/sci_media/images/chemical_reactions_involve_making_new_combinations/53823-2-eng-NZ/chemical_reactions_involve_making_new_combinations_full_size_landscape.jpg
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Forms of Energy
• ENERGY = capacity to cause change
• Energy exists in various forms (some of which can perform work)
• Energy can be converted from one form to another
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KINETIC ENERGY – energy associated with motion– HEAT (thermal energy) is kinetic
energy associated with random movement of atoms or molecules
POTENTIAL ENERGY = energy that matter possesses because of its location or structure
– CHEMICAL energy is potential energy available for release in a chemical reaction
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On the platform, the diver hasmore potential energy.
Diving convertspotential energy to kinetic energy.
Climbing up converts kinetic energy of muscle movement to potential energy.
In the water, the diver hasless potential energy.
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THERMODYNAMICS = the study of energy transformations
• CLOSED system (EX: liquid in a thermos) = isolated from its surroundings
• OPEN system energy + matter can be transferred between the system and its surroundings
• Organisms are open systems
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The First Law of Thermodynamics
= energy of the universe is constant
– Energy can be transferred and transformed
– Energy cannot be created or destroyed
• The first law is also called the principle of CONSERVATION OF ENERGY
http://www.pxleyes.com/photoshop-picture/4a3b747566555/remote-control.htmlhttp://www.suncowboy.com/solar101.php
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The Second Law of Thermodynamics
During every energy transfer or transformation
•entropy (disorder) of the universe INCREASES
•some energy is unusable, often lost as heat
http://hyperphysics.phy-astr.gsu.edu/hbase/therm/entrop.html
http://www.janebluestein.com/articles/whatswrong.html
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Chemical energy
Heat
CO2
First law of thermodynamics Second law of thermodynamics
H2O
ORGANISMS are energy TRANSFORMERS!
Spontaneous processes occur without energy input; they can happen quickly or slowly
For a process to occur without energy input, it must increase the entropy of the universe
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Free-Energy Change (G) can help tell which reactions will happen
∆G = change in free energy ∆H = change in total energy (enthalpy) or change ∆S = entropy T = temperature
∆G = ∆H - T∆S
•Only processes with a negative ∆G are spontaneous
•Spontaneous processes can be harnessed to perform work
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Exergonic and Endergonic Reactions in Metabolism
• EXERGONIC reactions (- ∆G)
• Release energy
• are spontaneous
ENDERGONIC reactions (+ ∆G)
• Absorb energy fromtheir surroundings
• are non-spontaneous
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Concept 8.3: ATP powers cellular work by coupling exergonic reactions to endergonic reactions• A cell does three main kinds of work:
– Mechanical
– Transport
– Chemical
• In the cell, the energy from the exergonic reaction of ATP hydrolysis can be used to drive an endergonic reaction
• Overall, the coupled reactions are exergonic
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Phosphate groups
Ribose
Adenine
ATP (adenosine triphosphate) is the cell’s renewable and reusable energy shuttle
ATP provides energy for cellular functions
Energy to charge ATP comes from catabolic reactions
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LE 8-9
Adenosine triphosphate (ATP)
Energy
P P P
PPP i
Adenosine diphosphate (ADP)Inorganic phosphate
H2O
+ +
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P
i
ADP
Energy for cellular work
provided by the loss of
phosphate from ATP
Energy from catabolism
(used to charge up
ADP into ATP
ATP
+
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Endergonic reaction: DG is positive, reaction is not spontaneous
Exergonic reaction: DG is negative, reaction is spontaneous
G = +3.4 kcal/mol
G = –7.3 kcal/mol
G = –3.9 kcal/mol
NH2
NH3Glu Glu
Glutamicacid
Coupled reactions: Overall DG is negative;Together, reactions are spontaneous
Ammonia Glutamine
ATP H2O ADP P i
+
+ +
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LE 8-11
NH2
Glu
P i
P i
P i
P i
Glu NH3
P
P
P
ATPADP
Motor protein
Mechanical work: ATP phosphorylates motor proteins
Protein moved
Membraneprotein
Solute
Transport work: ATP phosphorylates transport proteins
Solute transported
Chemical work: ATP phosphorylates key reactants
Reactants: Glutamic acidand ammonia
Product (glutamine)made
+ +
+
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Every chemical reaction between molecules involves bond breaking and bond forming
ACTIVATION ENERGY = amount of energy required to get chemical reaction started
Activation energy is often supplied in the form of heat from the surroundings
http://www.chuckwagondiner.com/art/matches.jpghttp://plato.acadiau.ca/COURSES/comm/g5/Fire_Animation.gif
IT’S LIKE PUSHING A SNOWBALL UP A HILL . . . Once you get it up there, it can roll down by itself
Free energy animation
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LE 8-14
Transition state
C D
A B
EA
Products
C D
A B
G < O
Progress of the reaction
Reactants
C D
A B
Fre
e en
erg
y
The Activation Energy Barrier
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CATALYST = a chemical agent that speeds up a reaction without being consumed by the reaction
ENZYMES = biological catalystsMost enzymes are PROTEINS Exception = ribozymes (RNA) Ch 17 & 26
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Course ofreactionwithoutenzyme
EA
without enzyme
G is unaffectedby enzyme
Progress of the reaction
Fre
e en
erg
y
EA withenzymeis lower
Course ofreactionwith enzyme
Reactants
Products
ENZYMES work by LOWERING ACTIVATION ENERGY;
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ENZYMES LOWER ACTIVATION ENERGY BY– Orienting substrates correctly
– Straining substrate bonds
– Providing a favorable microenvironment
Enzymes change ACTIVATION ENERGY
but NOT energy of REACTANTS or
PRODUCTShttp://sarahssureshots.wikispaces.com/Focus+on+Proteinshttp://www.ac-montpellier.fr/sections/personnelsen/ressources-pedagogiques/education-artistique/consultation-avis-du
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ENZYMES• Most are proteins
• Lower activation energy• Specific• Shape determines function• Reusuable• Unchanged by reaction
Image from: http://www.hillstrath.on.ca/moffatt/bio3a/digestive/enzanim.htm
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• The REACTANT that an enzyme acts on = SUBSTRATE
• Enzyme + substrate = ENZYME-SUBSTRATE COMPLEX
• Region on the enzyme where the substrate binds = ACTIVE SITE
• Substrate held in active site by WEAK interactions (ie. hydrogen and ionic bonds)
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TWO MODELS PROPOSED
• LOCK & KEYActive site on enzymefits substrate exactly
• INDUCED FITBinding of substrate causes changein active site so it fits substratemore closely
http://www.grand-illusions.com/images/articles/toyshop/trick_lock/mainimage.jpghttp://commons.wikimedia.org/wiki/File:Induced_fit_diagram.png
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– General environmental factors, such as temperature, pH, salt concentration, etc.
– Chemicals that specifically influence the enzyme
http://www.desktopfotos.de/Downloads/melt_cd.jpg http://www.nealbrownstudio.com/adm/photo/163_nb_fried_egg.jpg
See a movieChoose narrated
Enzyme Activity can be affected by:
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TEMPERATURE & ENZYME ACTIVITY
Each enzyme has an optimal temperature at which it can function (Usually near body temp)
http://www.animated-gifs.eu/meteo-thermometers/001.htm
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Increasing temperature increases the rate of an enzyme-catalyzed reaction up to a point.Above a certain temperature, activity begins to decline because the enzyme begins to denature.
http://www.uic.edu/classes/bios/bios100/lectures/chemistry.htm
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pH and ENZYME ACTIVITYEach enzyme has an optimal pH at which it can
function
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COFACTORS = non-protein enzyme helpers
• EX: Zinc, iron, copper
COENZYMES = organic enzyme helpers
• Ex: vitamins
http://www.wissensdrang.com/media/wis9r.gif
http://www.elmhurst.edu/~chm/vchembook/595FADcoq.html
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SUBSTRATE CONCENTRATION & ENZYME ACTIVITY
V MAX←
Adding substrate increases activity up to a point
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REGULATION OF ENZYME PATHWAYS• GENE REGULATION
cell switches on or off the genes that code for specific enzymes
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REGULATION OF ENZYME PATHWAYS• FEEDBACK INHIBITION
end product of a pathway interacts with and
“turns off” an enzyme earlier in pathway
• prevents a cell from wasting chemical resources by synthesizing more product than is needed
FEEDBACK INHIBITION
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NEGATIVE FEEDBACK
– An accumulation of an end product slows the process that produces that product
B
A
C
D
Enzyme 1
Enzyme 1
Enzyme 2
Enzyme 3
DD D D
D
D
DD
DD
C
B
A Negative feedback
Example: sugar breakdown generates ATP; excess ATP inhibits an enzyme near the beginning of the pathway
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POSITIVE FEEDBACK (less common)
– The end product speeds up production WW
X
Y
Z
ZZ
ZZ
Z
Z Z Z
Z Z Z Z
Z
ZZ Z
ZZ
Y
X
Enzyme 4
Enzyme 5
Enzyme 6
Enzyme 4
Enzyme 5
Enzyme 6
Positivefeedback
EXAMPLE: Chemicals released by platelets that accumulate at injury site, attract MORE platelets to the site.
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REGULATION OF ENZYME ACTIVITY• ALLOSTERIC REGULATION
protein’s function at one site is affected by binding of a regulatory molecule at another site
• Allosteric regulation can inhibit or stimulate an enzyme’s activity
http://bio.winona.edu/berg/ANIMTNS/allostan.gif
Allosteric enzyme inhibition
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SOME ALLOSTERIC ENZYMES HAVE MULTIPLE SUBUNITS
• Each enzyme has active and inactive forms
• The binding of an ACTIVATOR stabilizes the active form
• The binding of an INHIBITOR stabilizes the inactive form
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Substrate
Binding of one substrate molecule toactive site of one subunit locks allsubunits in active conformation.
Cooperativity another type of allosteric activation
Stabilized active formInactive form
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COOPERATIVITY = form of allosteric regulation that can amplify enzyme activity
Binding of one substrate to active site of one subunit locks all subunits in active conformation
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COMPETITIVE inhibitor REVERSIBLE; Mimics substrate and competes with substrate for active site on enzyme
ENZYMEANIMATION
Enzyme Inhibitors
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Enzyme Inhibitors
NONCOMPETITIVE inhibitors bind to another part of an enzyme, causing the enzyme to change shape and making the active site less effective
ENZYMEANIMATION