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Chapter 8: Intro to
Metabolism
Energy:
Defined:
The capacity to do work
Energy
1. Potential
2. Kinetic
3. Thermal
4. Chemical
Thermodynamics
Study of E transformations that
occur in a collection of matter
System: matter under study
Surroundings: rest of the universe
Closed vs. Open systems
1st Law of Thermodynamics
Law of Conservation of Energy
E in the universe is constant
E changes form
not created
not destroyed
2nd Law of Thermodynamics
Entropy- measure of
disorder or randomness
2nd Law of Thermodynamics
Every E transfer or transformation
increases the entropy of the
universe
Order can be increased locally, but
Entropy in the universe is
unstoppable (snowball effect)
Recycling E
Why can’t organisms recycle their E?
During transformations, some E
becomes unusable energy (heat)
Most E from food is lost as heat
Heat is only a useable form of E if
there is a temperature difference in a
system
What happens to the Heat
The unusable energy creates
disorder in the universe
More structured molecules
have less entropy, as they are
broken down, they are less
ordered.
Spontaneity
For a process or chemical
reaction to occur
spontaneously, it must
increase the entropy of the
universe
Living Systems
Increase the entropy of the universe
Organisms takes in matter and
energy from the surroundings and
replaces them with less ordered
forms
E: enters the ecosystem as light
leaves as heat
Metabolism
Sum of all the chemical
reactions inside an organism
Interactions between
molecules in an orderly
cellular environment
Metabolic Pathway
Start with a specific molecule that is
altered in a series of defined steps
Each chemical reaction in the pathway
is catalyzed by a specific enzymeexample: urease (30,000
molecules/sec)
These enzymes have the ability to be
turned off and on
Two types of metabolic pathways:
Catabolic Pathways
Breakdown pathways
“Downhill”
Anabolic pathways
Biosynthetic pathway
Uphill pathway
Anabolic vs. Catabolic
Which pathway is spontaneous?
Which pathway requires
energy?
Where does the energy come
from?
Which pathway increases
entropy?
Examples of anabolic and
catabolic pathways:
Protein synthesis
Metabolism of glucose (glycolysis)
Energy flow and
metabolism:
Energy released from downhill,
catabolic pathways can be stored
and used for uphill anabolic
pathways.
Gibb’s Free E of a System
(G)
Measures the portion of a system’s
E that can perform work when
temp and pressure are uniform
throughout the system
ΔG = ΔH – TΔS
*Can tell us if a process occurs
spontaneously
*- ΔG = spontaneous reaction
Free energy and
spontaneity:
ΔG = G final state – G initial state
Spontaneity cont.
For a process to occur
spontaneously,
1. enthalpy must decrease
2. temperature and entropy must
increase
3. both of these processes must
occur
Free Energy and Stability:
During a spontaneous reaction, the
reactants are more unstable than the
products, the reactants have a higher G
Unstable systems = high G
Tendency is towards stability
Examples:
Dye in water
Glucose
These systems will move
towards stability unless
something prevents it.
Equilibrium and Free
Energy:
When a system is in
equilibrium, G is at its lowest
possible value
Systems never spontaneously
move away from equilibrium
ΔG and Metabolism
Exergonic Reaction: net release of
free energy:
occurs spontaneously.
ΔG is negative- value represents
the amount of energy available
Cellular respiration
ΔG and Metabolism
Endergonic: absorbs free energy
from its surroundings.
ΔG is positive – value represents
the amount of energy required
to drive the reaction
Absorbs free energy
Non spontaneous
Exergonic vs. Endergonic
Exergonic = downhill
Endergonic = uphill
Preventing Equilibrium
If a cell reaches a metabolic
equilibrium it would die. There would
be no free energy to do work.
The constant flow of materials in and
out of cells keeps the metabolic
pathways from reaching equilibrium
(open system)
The coupling of
reactions:
The cell performs three types of
work: what are they?
Cell Work:
1. Mechanical Work:
2. Transport Work:
3. Chemical Work:
What’s ATP:
Adenosine Triphosphate
Composed of:
1. Adenine
2 Ribose
3. 3 PO43-
The Structure of ATP
ATP
Converting ATP to ADP + Pi
hydrolysis
releases approx. 7.3 kcal/mol
High amount of energy in relation to
what other molecules can deliver
Is this exergonic or endergonic?
ATP
Tri- phosphate region of ATP is very
unstable:
Must lose its terminal phosphate to
become more stable
Releasing energy
Chemical change to a state of lower free
energy
How ATP works
Energy coupling:
ATP hydrolysis (exergonic) is coupled
with some endergonic process
Requires the transfer of the terminal
phosphate group
The recipient then becomes
phosphorylated
Requires enzymes
The phosphorylated
intermediate is much more
reactive than its original
form.
Back to cell work:
1. Mechanical: ATP phosphorylates the movement of
motor proteins
2. Transport: ATP phosphorylates the transport of
sodium and potassium against their concentration
gradients
3. Chemical: ATP phosphorylates key reactants into a
desired product
Example: the amino acid glutamine is synthesized
from glutamic acid and ammonia
ATP Regeneration
Free E to create ATP comes from
catabolic(exergonic) reactions.
Phosphorylation of ADP
ATP Cycle:
Energy coupling
The shuttling of inorganic phosphate
and energy
Coupling of exergonic and endergonic
processes
10 million ATP molecules are consumed
and regenerated per second per cell.
How much energy is required to
make ATP?
ΔG = +7.3 kcal/mol
Spontaneous or non-spontaneous?
Chemical Reactions
Spontaneous reactions do require some
source of energy?????
Usually in the form of a catalyst
Enzymes
Regulates the rate of metabolic
reactions
Slows down or stops spontaneous
reactions
Chemical Reaction Logistics
Involves bond breaking and bond
formation
See metabolism of sucrose
Involves contorting one of the
molecules into an unstable state
Requires the absorption of energy
Activation Energy (EA)
Energy required to start a chemical
reaction
E needed by the molecule to
contort into its unstable shape
Uphill process = increase in free
energy
Exergonic Reaction
Enzymes and EA
Heat is usually provided to reach
transition state
Heat would break down complex
structures like proteins, DNA, etc.
Heat is also not selective enough for
biological processes
Enzymes hasten chemical reaction by
lowering the EA
Enzyme Terminology
Substrate
Active Site
Induced Fit
Enzymes
Substrate is held in active site by weak
bonds
R groups in active site catalyze the
conversion of the substrate
Most metabolic reactions are reversible
An enzyme will always catalyze in the
direction of equilibrium
4 Mechanisms of Enzyme Function
1. Active site is template: orientation
2. Stretch the substrate molecules:
distortion into transition state
3. Microenvironment
4. Direct participation: brief covalent
bond
pH and Temperature
Higher temperature help increase
the rate of reaction, but at a
certain point higher temps may
denature the enzyme
Thermophilic bacterial enzymes
Every enzyme also has an optimal
pH
Cofactors
Nonprotein “helper” for catalytic
activity
Bound tightly or loosely to
enzyme
Inorganic: zinc, iron, and copper
Organic (coenzyme): vitamins
Enzyme Inhibition
Competitive: directly block binding
of substrate to active site by
mimicking shape of the substrate
Noncompetitive: do not attach to
active site
binding of this molecule alters the
shape of the enzyme including the
active site
Penicillin
Allosteric Regulation
Regulation of an enzymes active
site
Regulatory molecule binds to
allosteric site
Inhibits or stimulates enzyme
activity
Allosteric site: where subunits join
Allosteric Regulation
Most of these enzymes have multiple
polypeptide chains each having an
active site
Involves conformational change in one
subunit which is transmitted to all other
subunits
Cooperativity
Active site bonding of 1 of
the subunits locks all other
active sites in the enzyme
into active conformation
Feedback Inhibition
A Metabolic pathway is switched
off by the inhibitory binding of the
end product to an enzyme that
acts earlier in the pathway
Dependent on concentration of
products