2. Energy
Energy is the capacity to do work, or the
capacity for change.
Energy transformations are linked to
chemical transformations (reactions) in
cells.
3. Types of Energy
Potential energy: is stored energy
- chemical bonds
- concentration gradient
- charge imbalance, etc.
Kinetic energy: is the energy of movement
4. Biochemistry
Metabolism: Sum total of all chemical reactions
in an organism.
Anabolic reactions: Complex molecules are
made from simple molecules; energy input is
required.
Catabolic reactions: Complex molecules are
broken down to simpler ones and energy is
released.
5. Laws of Thermodynamics
Thermo - “energy”
Dynamics - “change”
Apply to all matter and all energy
transformations in the universe.
6. First Law of Thermodynamics
Energy is neither created nor destroyed.
When energy is converted from one form
to another, the total energy before and
after the conversion is the same.
7. Second Law of
Thermodynamics
When energy is converted from one form to
another, some of that energy becomes
unavailable to do work.
No energy transformation is 100% efficient.
8. How is Energy Related…
In any system:
Total energy = usable energy + unusable energy
enthalpy (H) = free energy (G) + entropy (S)
H = G + TS (T = absolute temperature)
G = H – TS
Entropy is a measure of the disorder in a system.
9. Energy to do Work
Change in free energy (ΔG) in a reaction is
the difference in free energy of the
products and the reactants.
ΔG = ΔH – TΔS
•If ΔG is negative, free energy is released
•If ΔG is positive, free energy is consumed
•At chemical equilibrium, ΔG = 0
12. ATP
ATP (adenosine triphosphate) captures
and transfers free energy.
ATP releases a large amount of energy
when hydrolyzed.
ATP can phosphorylate, or donate
phosphate groups to other molecules.
15. Catalysts
Speed up the rate of a reaction.
The catalyst is not altered by the
reactions.
Most biological catalysts are enzymes
(proteins) that act as a framework in
which reactions can take place.
16. Enzymes
Highly specific
Reactants are called substrates
Substrate molecules bind to the active
site of the enzyme
The three-dimensional shape of the
enzyme determines the specificity
17. Enzymes
The enzyme-substrate complex (ES) is held together by
hydrogen bonds, electrical attraction, or covalent bonds.
E + S → ES → E + P
The enzyme may change when bound to the substrate, but
returns to its original form.
18. Enzymes Lower the Energy Barrier
for Reactions
Activation Energy:
The amount of energy
needed to initiate a
reaction
All reactions require
activation energy.
Exergonic vs.
Endergonic Reactions
20. The rate of a catalyzed reaction
depends on substrate concentration
Concentration of an
enzyme is usually
much lower than
concentration of a
substrate.
At saturation, all
enzyme is bound to
substrate
21. Enzyme Regulation
Inhibitors: 2 Groups of Inhibitors:
Molecules that bind to - Reversible
the enzyme and slow - Irreversible
reaction rates.
Irreversible inhibition:
Naturally occurring Inhibitor covalently
bonds to side chains
inhibitors regulate
in the active site and
metabolism.
permanently
inactivates the
enzyme.
22. Naturally Occurring Inhibitors
Reversible inhibition: Inhibitor bonds
noncovalently to the active site and prevents
substrate from binding.
2 Types:
– Competitive Inhibitors
– Noncompetitive Inhibitors
23. Competitive Inhibitors
Compete with the
natural substrate for
binding sites.
When concentration of
competitive inhibitor
is reduced, it detaches
from the active site.
24. Noncompetitive Inhibitors
Bind to the enzyme at
a different site (not the
active site).
The enzyme changes
shape and alters the
active site.
25. Metabolic Pathways
Metabolism is the thousands of
chemical reactions occurring in
cells simultaneously
These reactions are organized in
metabolic pathways.
Each reaction is catalyzed by a
specific enzyme.
The pathways are interconnected.
Regulation of enzymes and thus
reaction rates helps maintain
internal homeostasis.
26. Metabolic Pathways
The first reaction is the
commitment step—other
reactions then happen in
sequence.
Feedback inhibition (end-
product inhibition): The
final product acts as a
noncompetitive inhibitor
of the first enzyme, which
shuts down the pathway.
