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TRANSCRIPT
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Energy and Metabolism
Chapter 6
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Flow of Energy
• Thermodynamics
– Branch of chemistry
concerned with energy
changes
• Cells and biological
processes are governed
by the laws of physics
and chemistry
http://vinodwadhawan.blogspot.com/2011/12/5-can-you-unscramble-egg.html
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• Energy – capacity to
do work
– Two states
1. Kinetic – energy of
motion
2. Potential – stored
energy
– Many forms –
mechanical, heat,
sound, electric current,
light, or radioactivity 3
http://www.petervaldivia.com/technology/energy/
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a. Potential energy b. Kinetic energy
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• Energy – capacity to do work
– Heat is the most convenient way of measuring
energy • 1 calorie = heat required to raise 1 gram of water 1ºC
• calorie or Calorie (= 1000 calories)?
5
Potential energy Kinetic energy
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• Energy flows into the biological world from
the sun
– Photosynthetic organisms capture this energy
– Stored as potential energy in chemical bonds
6
http://utahscience.oremjr.alpine.k12.ut.us/sciber99/8th/energy/sciber/ecosys.htm
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Redox reactions
• Oxidation
– Atom or molecule loses an
electron
• Reduction
– Atom or molecule gains an
electron
– Higher level of energy than
oxidized form
• Oxidation-reduction
reactions (redox)
– Reactions always paired
http://www.green-planet-solar-energy.com/oxidation-reduction-reactions.html
Potential Kinetic
Kinetic Potential
Reduction
Oxidation
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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
e –
A B
A + B + A +
B –
Loss of electron (oxidation)
Gain of electron (reduction)
Lower energy Higher energy
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Laws of thermodynamics
• First law of thermodynamics
– Energy cannot be created nor
destroyed
– Energy can only change from
one form to another
– Total amount of energy in the
universe remains constant
– During each conversion, some
energy is lost as heat
9
http://biology200.gsu.edu/houghton/2107%20%2713/lecture18.html
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• Second law of
thermodynamics
– Entropy (disorder) is
continuously increasing
– Energy transformations
proceed spontaneously
to convert matter from a
more ordered/less stable
form to a less ordered/
more stable form
– Heat is lost from all
reactions http://biology200.gsu.edu/houghton/2107%20%2713/lecture18.html
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Disorder happens
spontaneously
Organization
requires energy
© Jill Braaten
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Free energy
• G = Energy available to do work (usable energy)
• G = H – TS
H = enthalpy, energy in a molecule’s chemical bonds
T = absolute temperature
S = entropy, unavailable energy (lost, unusable)
http://biology200.gsu.edu/houghton/2107%20%2713/lecture18.html
G S
H G = H – TS
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ΔG = ΔH – TS • ΔG = change in free energy
• Positive ΔG – Products have more free energy than reactants
– H is higher or S is lower
– Endergonic
– Not spontaneous, requires input of energy
• Negative ΔG – Products have less free energy than reactants
– H is lower or S is higher or both
– Exergonic
– Spontaneous (may not be instantaneous),
– Releases energy
13
Fre
e e
nerg
y
Initial state
(reactants)
Final state
(products)
ΔG > 0
Fre
e e
nerg
y
Initial state
(reactants)
Final state
(products)
ΔG < 0
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a.
b.
0
0
Course of Reaction
Products
G > 0
G < 0
Reactants
Reactants
Course of Reaction
Products
Fre
e E
nerg
y (
G)
En
erg
y R
ele
ase
d E
nerg
y S
up
plie
d
Fre
e E
nerg
y (
G)
En
erg
y R
ele
ase
d E
nerg
y S
up
plie
d
Energy is
released
Energy must
be supplied
Exergonic
Endergonic
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Activation energy
• Extra energy (EA) required to
destabilize existing bonds and
initiate a chemical reaction
• Exergonic reaction’s rate depends
on the activation energy required
– Larger activation energy proceeds
more slowly
• Rate can be increased 2 ways
1. Increasing energy of reacting
molecules (heating)
2. Lowering activation energy
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http://www4.nau.edu/meteorite/Meteorite/Book-GlossaryA.html
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ΔG
En
erg
y R
ele
as
ed
En
erg
y S
up
plie
d
Fre
e E
ne
rgy (
G) Activation
energy
Activation
energy 0
uncatalyzed
catalyzed
Course of Reaction
Product
Reactant
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Catalysts
• Substances that influence
chemical bonds in a way that
lowers activation energy
• Cannot violate laws of
thermodynamics
– Cannot make an endergonic
reaction spontaneous
• Do not alter the proportion of
reactant turned into product
17
http://www4.nau.edu/meteorite/Meteorite/Book-GlossaryA.html
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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
ΔG
En
erg
y R
ele
as
ed
En
erg
y S
up
plie
d
Fre
e E
ne
rgy (
G) Activation
energy
Activation
energy 0
uncatalyzed
catalyzed
Course of Reaction
Product
Reactant
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ATP
• Adenosine triphosphate
– Chief “energy currency” all cells use
– Composed of… • Ribose – 5 carbon sugar
• Adenine
• Chain of 3 phosphates – Key to energy storage
– Bonds are unstable
• ADP – 2 phosphates
• AMP – 1 phosphate – lowest energy form
http://chemwiki.ucdavis.edu/Physical_Chemistry/Thermodynamics/Case_Studies/Case_Study%3A_Thermodynamics_of_ATP
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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
AM
P C
OR
E
O
O–
O
O
O
H H H
H
O
C C
N N
N
C
N
C
C H H
P O–
O P
O P O
AD
P
AT
P
Triphosphate
group
O–
CH2
High-energy
bonds
a.
Adenine NH2
Ribose
OH OH
b.
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ATP cycle
• Exergonic ATP hydrolysis
drives coupled endergonic
reactions
– Coupled reaction results in net
–ΔG (exergonic & spontaneous)
• ATP not suitable for long-term
energy storage
– Fats and carbohydrates better
– Cells store only a few seconds
worth of ATP
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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
+
+
Pi
Energy from
exergonic
cellular
reactions
ATP H2O
ADP
Energy for
endergonic
cellular
processes
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Enzymes: Biological Catalysts
• Most enzymes are protein
– Some are RNA
• Shape of enzyme stabilizes a temporary association between substrates
• Enzyme not changed or consumed in reaction
http://www.ptj.com.pk/Web-2010/04-10/Muhammad-Ayaz-Shaikh.htm
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Enzymes: Biological Catalysts
• Example: Carbonic anhydrase (enzyme used to maintain blood pH)
– 200 molecules of carbonic acid per hour made without enzyme
– 600,000 molecules formed per second with enzyme
• Most enzymes end in -ase
http://www.chem.harvard.edu/groups/shakhnovich/people/kutchukian.html
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Active site
• Pockets or clefts for
substrate binding
• Precise fit of substrate into
active site
• Forms enzyme–substrate
complex
25
http://faculty.ccbcmd.edu/courses/bio141/lecguide/unit6/genetics/proteins/enzymes/enzsub.html
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Active site
• As the enzyme–substrate complex forms…
– The enzyme molecule changes shape slightly
(Induced fit) …
– Applies stress to distort particular bond to lower
activation energy to speed reaction
26 http://www.ptj.com.pk/Web-2010/04-10/Muhammad-Ayaz-Shaikh.htm
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Active site
a. b.
Enzyme Enzyme–substrate complex
Substrate
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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
1. The substrate, sucrose,
consists of glucose and
fructose bonded together.
2. The substrate binds to the active site
of the enzyme, forming an enzyme–
substrate complex.
3. The binding of the substrate and
enzyme places stress on the glucose–
fructose bond, and the bond breaks.
4. Products are
released, and
the enzyme is
free to bind other
substrates.
Bond Glucose
Fructose
Active site
Enzyme
sucrase
H2O
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• Enzymes may be suspended in the cytoplasm or attached to cell membranes and organelles
• Multienzyme complexes – subunits work together to form molecular machine – Product can be delivered easily to
next enzyme
– Unwanted side reactions prevented
– All reactions can be controlled as a unit
http://msb.bio.uni-goettingen.de/SFB860/Projects_b.html
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Nonprotein enzymes
• Ribozymes
– 1981 discovery that certain reactions catalyzed in cells by RNA molecule itself
– Two kinds 1. Intramolecular catalysis –
catalyze reaction on RNA molecule itself
2. Intermolecular catalysis – RNA acts on another molecule
http://chemistry.gsu.edu/faculty/Huang/ribozyme.htm
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Enzyme function
• Rate of enzyme-catalyzed
reaction depends on
concentrations of substrate
and enzyme (c)
• Any chemical or physical
condition that affects the
enzyme’s three-dimensional
shape can change rate…
– Optimum temperature (a)
– Optimum pH (b)
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http://academic.pgcc.edu/~kroberts/Lecture/Chapter%205/enzymes.html
What is happening here??
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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
a.
b.
Rate
of
Reacti
on
Optimum pH for pepsin
Rate
of
Reacti
on
pH of Reaction
Optimum pH for trypsin
1 2 3 4 5 6 7 8 9
30 40 50 60 70 80
Temperature of Reaction (˚C)
Optimum temperature
for human enzyme Optimum temperature for enzyme
from hotsprings prokaryote
What is happening here??
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Inhibitors • Inhibitor – substance that
binds to enzyme and
decreases its activity
• Competitive inhibitor
– Competes with substrate for
active site
– Physically blocks active site
– Typically reversible
http://biochemanics.wordpress.com/tag/reversible-inhibitors/
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Inhibitors
• Noncompetitive inhibitor
– Binds to enzyme at a site other
than active site (allosteric site)
– Causes shape change that
makes enzyme unable to bind
substrate
– Maybe irreversible (toxin) or
reversible (allosteric regulation)
http://biochemanics.wordpress.com/tag/reversible-inhibitors/
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a. Competitive inhibition b. Noncompetitive inhibition
Enzyme Enzyme
Allosteric site
Active
site
Competitive inhibitor interferes
with active site of enzyme so
substrate cannot bind
Noncompetitive inhibitor changes
shape of enzyme so it cannot
bind to substrate
Active
site
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Substrate Substrate
Inhibitor Inhibitor
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Allosteric Enzymes
• Allosteric enzymes – enzymes exist in active
and inactive forms
• Most noncompetitive inhibitors bind to allosteric
site – chemical on/off switch
http://www.biology.arizona.edu/biochemistry/problem_sets/energy_enzymes_catalysis/03t.html
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Allosteric Enzymes
• Allosteric inhibitor – binds to allosteric site and
reduces enzyme activity
• Allosteric activator – binds to allosteric site and
increases enzyme activity
http://www.biology.arizona.edu/biochemistry/problem_sets/energy_enzymes_catalysis/03t.html
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Metabolism
• Total of all chemical reactions carried out by
an organism
– Anabolic reactions/anabolism
• Expend energy to build molecules
• Anabolic steroids = build muscle
– Catabolic reactions/catabolism
• Harvest energy by breaking down molecules
• Starvation = breaks down muscle
Larger
molecules
Smaller
molecules +
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Energy and Energy
Conversions
• Summary of terms:
Catabolism Anabolism
Exergonic Endergonic
Kinetic Energy Potential Energy
Releases Stores
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Biochemical pathways
• Chemical reactions
that create/store or
produce other
chemical products
for daily function
• Reactions occur in
a sequence
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Biochemical pathways
• Product of one reaction is the substrate for the next reaction
• Some reactions such as glycolysis takes place in the cytoplasm; others such as the electron transport chain take place in organelles
• Enzymes in pathway maybe located within a single membrane
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Initial substrate
Intermediate
substrate A
Intermediate
substrate B
Intermediate
substrate C
End product
Enzyme1
Enzyme2
Enzyme3
Enzyme4
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Basic metabolic pathway chart
43
http://upload.wikimedia.org/wikipedia/commons/1/11/Metabolism_wip.png
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Feedback inhibition
• End-product of
pathway binds to an
allosteric site on
enzyme that catalyzes
first reaction in
pathway
• Shuts down pathway
so raw materials and
energy are not wasted
• Usually at or near first
step in pathway 44
b.
Enzyme 1
Enzyme 2
Enzyme 3 End product
Initial
substrate
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45
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
a.
Enzyme 1
Enzyme 2
Enzyme 3 End product
Initial
substrate
Intermediate
substrate A
Intermediate
substrate B
b.
Enzyme 1
Enzyme 2
Enzyme 3 End product
Initial
substrate
Biochemical pathway
lacking feedback
Biochemical pathway
with negative feedback
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Negative vs. Positive Feedback
• Negative feedback
(inhibition)
– Most common control type
– Downstream product
increases, this increase
level of product tells an
upstream factor that there is
enough and it slows or
stops the reaction.
• Blood pressure: standup fast,
HR increases to keep you
from passing out, then HR
returns to normal. 46
Blood pressure
decrease
Receptors in
carotids
Brain
Increase
heart rate
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Negative vs. Positive Feedback
• Positive feedback – Very few examples in normal physiology that have a good
outcome
– Downstream product tells the upstream system that more needs to be produced
• Childbirth: control of the contractions, the harder the babies head pushes on the cervix causes hormones to be produced that increase the muscle contraction. This continues until baby and placenta are delivered.
47 http://kageeamy2012.wikispaces.com/01
+Homeostasis+%26+Chemical+Aspects
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