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Monday, 9/10/12
• Reminder: Chp.8 Guided Reading homework
is due tomorrow
• Grades are posted on window
• Pass back Controlled Exp’t Packets, discuss
• Chp.8 Lecture/Notes
• 1st lab this week!
• Chp.4,5,8 Test next Monday
– Carbon, Biomolecules, Enzymes
Lecture Notes
• Chapter 8
~ An Introduction to
Metabolism
Key Concepts – from book
• (8.1) An organism’s metabolism
transforms matter and energy, subject to
the laws of thermodynamics
• (8.2) The free-energy change of a reaction
tells us whether or not the reaction occurs
spontaneously (energetically favorable,
process occurs without an input of energy).
Key Concepts Cont.
• (8.3) ATP powers cellular work by
coupling exergonic reactions to endergonic
reactions.
• (8.4) Enzymes speed up metabolic
reactions by lowering energy barriers.
• (8.5) Regulation of enzyme activity helps
control metabolism.
Metabolism/Bioenergetics
• Metabolism: The totality of an organism’s
chemical processes; managing the material
and energy resources of the cell
• Catabolic pathways: degradative process
such as cellular respiration; releases energy
• Anabolic pathways: building process such
as protein synthesis; photosynthesis;
consumes energy
Thermodynamics
• Energy (E)=capacity to do work; Kinetic energy~ energy of motion;
Potential energy~ stored energy
• Thermodynamics~ study of E transformations
• 1st Law: conservation of energy; E transferred/transformed, not
created/destroyed
• 2nd Law: transformations increase entropy (disorder, randomness)
• Combo: quantity of E is constant, quality is not
Free energy
• Free energy (G): portion of system’s E that can perform
work (at a constant T)
• Exergonic reaction: net release of free E to surroundings
• Endergonic reaction: absorbs free E from surroundings
Fig.8.14 Energy profile of an exergonic reaction
The reactants AB and CD must absorb
enough energy from the surroundings
to reach the unstable transition state,
where bonds can break.
A
B
C
D
Bonds break and new
bonds form, releasing
energy to the
surroundings.
Free energy
Transition state
A
B
C
D
EA
Reactants
A
B
C
D
∆G < O
Products
Progress of the reaction
Energy Concepts Video Clip
• 2 min.
Energy Coupling & ATP
• E coupling: use of exergonic
process to drive an endergonic
one
• Adenosine triphosphate (ATP)
• ATP tail: high negative
charge
• ATP hydrolysis: release of
free E
• Phosphorylation
(phosphorylated
intermediate)~ enzymes
Endergonic reaction: ∆G is positive, reaction
is not spontaneous
NH2
Glu
+
Glutamic
acid
NH3
Ammonia
∆G = +3.4 kcal/mol
Glu
Glutamine
Exergonic reaction: ∆ G is negative, reaction
is spontaneous
ATP
+
H2O
Coupled reactions: Overall ∆G is negative;
together, reactions are spontaneous
ADP
+
P
∆G = –7.3 kcal/mol
∆G = –3.9 kcal/mol
Figure 8.12 The ATP cycle
ATP hydrolysis to
ADP + P i yields energy
ATP synthesis from
ADP + P i requires energy
ATP
Energy from catabolism
(exergonic, energy yielding
processes)
ADP + P
i
Energy for cellular work
(endergonic, energyconsuming processes)
Enzymes
• Catalytic proteins: change the
rate of reactions w/o being
consumed
• Free E of activation
(activation E, EA): the E
required to break bonds
• Substrate: enzyme reactant
• Active site: pocket or groove
on enzyme that binds to
substrate
• Induced fit model
How Enzymes Work Video Clip
• 1 min.
QuickTime™ and a
Cinepak decompressor
are needed to see this picture.
Figure 8.13 Example of an enzymecatalyzed reaction: hydrolysis of
sucrose by sucrase
CH2OH
CH2OH
O
O
H H
H
H
OH
H HO
O
+ H2O
HO
CH2OH
H
OH H
OH
Sucrose
C12H22O11
Sucrase
CH2OH
O H
H
H
OH H
OH
HO
H
OH
Glucose
C6H12O6
CH2OH
O
HO
H HO
OH H
Fructose
C6H12O6
H
CH2OH
Fig.8.17 The active site and catalytic cycle
of an enzyme
1 Substrates enter active site; enzyme
changes shape so its active site
embraces the substrates (induced fit).
Substrates
2 Substrates held in
active site by weak
interactions, such as
hydrogen bonds and
ionic bonds.
3 Active site (and R groups of
its amino acids) can lower EA
and speed up a reaction by
• acting as a template for
substrate orientation,
• stressing the substrates
and stabilizing the
transition state,
• providing a favorable
microenvironment,
• participating directly in the
catalytic reaction.
Enzyme-substrate
complex
6 Active site
is available for
two new substrate
molecules.
Enzyme
5 Products are
Released.
Products
4 Substrates are
Converted into
Products.
Effects on Enzyme Activity
• Temperature (denature)
• pH
• Cofactors:
– inorganic, nonprotein
helpers; ex.: zinc, iron,
copper
• Coenzymes:
– organic helpers;
ex.:vitamins
Enzyme Inhibitors
• Irreversible (covalent);
reversible (weak bonds)
• Competitive: competes
for active site (reversible);
mimics the substrate
• Noncompetitive: bind to
another part of enzyme
(allosteric site) altering its
conformation (shape);
poisons, antibiotics
Allosteric Regulation
• Activators & Inhibitors
• Insert Feedback inhibition example/diagram
– Pg.157, Figure 8.21
Initial substrate
(threonine)
Active site
available
Threonine
in active site
Figure 8.21
Feedback
inhibition
in
isoleucine
synthesis
Enzyme 1
(threonine
deaminase)
Isoleucine
used up by
cell
Intermediate A
Feedback
inhibition
Active site of
enzyme 1 no
longer binds
threonine;
pathway is
switched off
Enzyme 2
Intermediate B
Enzyme 3
Intermediate C
Isoleucine
binds to
allosteric
site
Enzyme 4
Intermediate D
Enzyme 5
End product
(isoleucine)
After: if time
• Enzymes & Metabolism Worksheet
***Reminder: Chp.8 homework due
tomorrow!!!!