Transcript Chapter 6: Intro to Metabolism

Ch 6: Intro to Metabolism
Chapter 6: Intro to Metabolism

Metabolism  All of the chemical processes that
occur in a living organism.

Metabolic Pathways
 Specific, orderly, and stepwise series of chemical
reactions
 Manage the material and E resources of the cell.
Metabolic Pathways

Catabolic Pathways
 Breakdown resources to release E.
 Complex Molecule  Simple Molecules
 Ex: C6H12O6 (glucose) CO2 + H2O + E
 Always release E stored in the bonds of complex
molecules.

Anabolic Pathways
 Simple Molecule  Complex Molecules
 Require the usage of E.
Bioenergetics

Bioenergetics is the study of how
organisms manage their E resources.

Catabolic reactions provide the E needed
for anabolic reactions.
Energy
Capacity to do work. (work = pretty much
everything)
 Various forms (light, chemical, heat, mech.)
 organisms live because of their ability to
transform that E from one form to another.
 Conversions are governed by the laws of
thermodynamics.

Energy Conversions



Kinetic Energy  E possessed by matter that is in
motion.
Potential Energy  E stored by matter because of
location or structure.
 Ex: Water behind a dam, gasoline, glucose
Light E  Chemical E  Kinetic E
- Conv. 1 (Plants)  Photosynthesis
- Conv. 2 (Animals)  Cell. Respiration
Thermodynamics

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
Open System  Matter under study as well as all of
its surroundings. (Organisms = Open)
Closed System  Matter under study is isolated
from its surroundings.
In open systems, E (and matter) flows freely between
the matter (organisms) and its surroundings.
Organisms are open systems, can you list what they
absorb from and release to their surroundings?
1st Law of Thermodynamics
E
cannot be created nor destroyed, only
transferred and transformed.
 But, if E can’t be destroyed, why don’t
organisms act as closed systems and
recycle E?
2nd Law of Thermodynamics
 Measure of disorder,
randomness. Greater disorder,
randomness = higher entropy.
 Every E transfer or transformation
increases the entropy (disorder) of the
universe. (Ex: the universe = your
bedroom)
 Entropy
nd
2
Law of Thermodynamics
Every E transfer generates some heat.
 Heat is E in its most random state (least
usable form).
 This 2nd Law is why organisms need to
constantly replenish their E and remain
open systems.

Thermodynamics

Amount of E in the organisms universe is
constant, its quality is not.

Organisms take organized forms of matter
from their surroundings, and replace them with
less ordered forms.
 For example, E flows into an ecosystem as
light (less random) and leaves as heat (more
random)
Spontaneous Reactions

Certain processes occur spontaneously, while
others are non-spontaneous.

A spontaneous change is one that takes place
without outside help. (Ex: Water flows
downhill)

It can be predicted whether or not a certain
change will be spontaneous.
Free Energy
The portion of a system’s E that is available to
perform work (at uniform temp.)
 Free energy (G) is dependent upon:
 The system’s total energy (H)
 The temperature (T)
 The change in entropy (ΔS)

ΔG = ΔH - TΔS
Free Energy and Spontaneity
 ΔG
determines rxn spontaneity.
(
- ) ΔG = spontaneous
 ( + ) ΔG = non-spontaneous
@
Equilibrium, ΔG = 0
Exergonic vs Endergonic Rxns
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Exergonic reactions produce E, while
endergonic reactions absorb E.

Exergonic = (-) ΔG values and are spontaneous.

Endergonic = (+) ΔG values and are nonspontaneous.
Metabolic Disequilibrium
If the ΔG of the metabolic processes in a living
cell = 0, then the cell is dead.
 Disequilibrium keeps the cell alive.
 Metabolic Pathways
 Products of one step as reactants in another.
 Energy coupling
 Exergonic reactions power endergonic
reactions.
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ATP Couples Exergonic/Endergonic
Reactions
Cells do three kinds of work:
 Mechanical (muscles, chromosome
movement)
 Transport (pumping across membranes)
 Chemical (anabolic (endergonic) reactions)
 ATP is the immediate E source for cellular
work.

Structure of ATP
(Adenosine Tri-Phosphate)

Adenine + Ribose + 3 Phosphate groups
Hydrolysis of ATP

Hydrolysis is when water is added to a
compound and a bond is broken.

When ATP is hydrolyzed, its products are:
ADP (di-phosphate) + Phosphate + Energy
Hydrolysis of ATP
Phosphorylation (ATP E Transfer)
Transfer P = Transfer E
 This phosphorylated intermediate is more
reactive than the original molecule and now has
been “energized”.
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ENZYMES
Proteins
 Speed up (catalyze) chemical reactions
 Lower the E barrier to a chemical reaction.
 Not consumed in the reactions.
 Every reaction has an initial E barrier
(activation E) that must be overcome.
 Do not change the ΔG of the reaction.
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Catalyzed vs Uncatalyzed Rxns
Enzyme Specificity

Substrates are the reactants that enzymes work
upon.

While the enzyme is bound to its substrate, the
substrate is converted into the product.

The specificity of enzymes is directly related to
their shape and the shape of the substrate.
Enzyme-Substrate Complex

active site -- region of the enzyme that binds to the
substrate.
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The specificity of an enzyme is due to a compatible fit
between the active site and the substrate. (Lock and
Key)
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Induced Fit
 When the substrate enters the enzymes active site,
the enzyme changes shape to fit even better with
the substrate.
Enzyme-Substrate Complex
Weak interactions (H-bonds, ionic bonds)
 This often orients the substrate in such a way as
to make it more reactive.
 Once the reaction is complete, the enzyme and
substrate separate.
 Often, the active site provides a
microenvironment (Ex: low pH) more
conducive to specific reaction.
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Factors Affecting Enzymes

Enzyme function is highly dependent upon
temperature and pH.

Each enzyme has an optimal range for each.
 Optimal orientation within its ranges.
Factors Affecting Enzymes
Cofactors and Coenzymes
Some enzymes require the help of other atoms,
ions or molecules to operate.
 Cofactors- Nonprotein inorganic helpers (Ex:
Zn, Fe, Cu)
 CoEnzymes – Nonprotein organic helpers
(generally vitamins)
 Generally aid by binding to enzyme and helping
it orient itself more efficiently.

Enzyme Inhibition

Some chemicals inhibit the action of enzymes.

Competitive inhibitors compete with the
substrate for the active site.
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Noncompetitive inhibitors
 bind elsewhere on the enzyme
 changes the orientation to a less effective
position.
Enzyme Inhibition
Metabolic Control

-
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Allosteric
Control
A regulatory
molecule binds
to enzyme and
changes its shape
Enzymes have
two orientations
(active or
inactive)
Feedback Inhibition
Metabolism’s “thermostatic” control
 When the end-product of a reaction
accumulates in the cell, it can cause the pathway
to be inhibited.
 The end-product acts as an enyzme inhibitor
(generally allosteric inhibition)
 Prevents cell from wasting E

Cooperativity
Some enzymes have multiple subunits with
multiple active sites
 When a substrate binds to one active site, it
often causes a domino effect and triggers the
enzyme to bind to additional substrate
molecules
 Binding of first substrate causes favorable
allosteric change in enzyme configuration
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Metabolic Organization
Remember, metabolism is an ordered, stepwise
set of chemical reactions.
 Therefore, enzymes are found in structures
throughout the cell to make their use more
efficient.
 For example, enzymes for cellular respiration are
found in mitochondria (where they will be
needed)
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