Download Chapter 5B: Energy & Enzymes 1. What is Energy?

Chapter 5B:
Energy & Enzymes
1. What is Energy?
2. Energy & Chemical Reactions
3. ATP
4. Enzymes & Metabolic Pathways
1. What is Energy?
2 Basic Forms of Energy
Kinetic Energy (KE)
• energy in motion or “released” energy:
heat (molecular motion)
*electric current (flow of charged particles)
*light energy (radiation of photons)
*mechanical energy (structural movement)
*chemical energy (breaking covalent bonds,
flow from high to low concentration)
*forms of KE cells use to “do things”
Potential Energy (PE)
• stored energy (i.e., not yet released):
gravitational potential
*chemical bonds
*chemical, charge gradients
*sources of PE cells rely on
Illustration of Kinetic &
Potential Energy
KE highest at B, lowest at A & C
PE highest at A & C, lowest at B
2 Laws of Thermodynamics
1st Law of Thermodynamics
Conservation of energy:
“energy is neither created nor destroyed, but may
be converted to other forms”
2nd Law of Thermodynamics
Energy conversions:
“in any energy conversion, some usable energy is
always lost”
• “Lost” energy = energy released as heat to the
surroundings, energy that can’t be used
NO energy conversion is 100% efficient!
Energy conversion
Fuel
Waste
products
Heat
energy
Carbon dioxide
Gasoline
Combustion
Kinetic energy
of movement
Water
Oxygen
Energy conversion in a car
Heat
Glucose
Cellular respiration
Oxygen
Carbon dioxide
Water
Energy for cellular work
Energy conversion in a cell
2. Energy & Chemical
Reactions
Exergonic
Chemical
Reactions
Potential energy of molecules
loss of PE
• net release
of energy
Reactants
Amount of
energy
released
Energy released
Products
• loss of PE,
converted
to KE
Endergonic
Chemical
Reactions
gain of PE
• increases PE
Potential energy of molecules
• net consumption
of energy
Products
Energy required
Reactants
Amount of
energy
required
gain of PE Photosynthesis
is Endergonic
• energy input
from sunlight
• stored in glucose
Respiration is
Exergonic
• releases PE
stored in glucose
loss of PE
Activation Energy (Ea)
Whether endergonic or exergonic, all chemical
reactions require some energy input for the
reaction to proceed: the activation energy (Ea)
• all reactions require some sort of “spark”
• this is why sources of chemical PE are “stable”
Mechanical Model of
Activation Energy
The upright bottle falling over is analogous to an
exergonic reaction, yet it still requires some
energy input for the bottle to tip over.
3. ATP
Adenosine Triphosphate (ATP)
Adenosine
Chemical PE in
molecules of ATP
is the principal
source of directly
useable energy in
cells.
Triphosphate (ATP)
Phosphate
group
Adenine
Ribose
hydrolysis
• “food energy” is
transferred to ATP
by respiration
+
Adenosine
Diphosphate (ADP)
gain of PE
ATP synthesis
is Endergonic
• energy input is
needed to add
a 3rd phosphate
ATP “hydrolysis”
is Exergonic
loss of PE
• breaking the
covalent bond
with the 3rd PO4
releases energy
Coupling of Biochemical Reactions
Exergonic reactions fuel (provide energy for)
endergonic reactions in cells (i.e, they are “coupled”)
• breakdown of
glucose fuels
ATP production
exergonic
endergonic
exergonic
endergonic
• ATP hydrolysis
fuels most
cellular activities
Examples of ATP-powered “Work”
ATP
Chemical work
Mechanical work
Transport work
membrane
protein
P +
motor
protein
solute
P
P
Reactants
P
P
P
Product
Molecule formed
Protein moved
ADP + P
Solute transported
4. Enzymes &
Metabolic Pathways
Enzymes are Biological Catalysts
Enzymes are proteins that increase the rates of
reactions by lowering the E
a
• the enzymes themselves are not changed
Reaction
without
enzyme
EA without
enzyme
Energy
EA with
enzyme
Reactants
Reaction with
enzyme
Net
change
in energy
(the same)
Products
Progress of the reaction
• allows
reactions
to occur
that
otherwise
could not
The catalytic cycle of an enzyme
1 Enzyme available
with empty active
site
Active site
• every enzyme has a
unique substrate &
thus catalyzes a
specific reaction
Substrate
(sucrose)
2 Substrate binds to
enzyme with induced fit
Glucose
Enzyme
(sucrase)
Fructose
H 2O
4 Products are
released
3 Substrate is
converted to
products
• cells produce
1000s of different
enzymes, all of
which are proteins
encoded by a
particular gene
Metabolic Pathways
Most biological processes, whether anabolic
(building) or catabolic (breaking down), require
a series of chemical reactions (i.e., a pathway)
• each step in a metabolic pathway is catalyzed by a
specific enzyme
A Simple Metabolic Pathway
Regulation of
Metabolic Pathways
Most metabolic pathways are regulated so that
“too much” is not produced:
• e.g., Feedback Inhibition: excess product inhibits
the activity of an enzyme early in the pathway
Inhibitors prevent substrate binding
Substrate
Active site
Enzyme
• provides a
means to
regulate
enzyme
activity
Normal binding of substrate
Competitive
inhibitor
Noncompetitive
inhibitor
Enzyme inhibition
• many
poisons
inhibit
enzyme
activity
Key Terms for Chapter 5B (5.10-16)
• kinetic, potential energy
• endergonic, exergonic, coupling of reactions
• activation energy
• ATP, enzyme, catalyst
• substrate, active site
• competitive, noncompetitive inhibition
Relevant Review Questions:
2, 4, 7, 12, 14, 17