ENERGY &
METABOLISM
Properties/ Characteristics of Enzymes
1. Are organic catalysts which change the
RATE of a chemical reaction
2. All are globular proteins
Properties/ Characteristics of Enzymes
3. Some enzymes depend upon
COENZYMES to catalyze the reaction
(ex: NAD+, NADP, FAD)
4. Coenzymes are organic molecules
(“B” vitamin derivatives) which assist a
specific enzyme in a specific reaction
Properties/ Characteristics of Enzymes
5. Are temperature
sensitive-- they work
most efficiently at an
optimum
temperature
6. Most are denatured at
temperatures
above 42o C
Properties/ Characteristics of Enzymes
7. Are pH sensitivemost react between
pH 6-8, except for
gastric enzymes
8. Enzymes are
specific to a given
substrate
Properties/ Characteristics of Enzymes
9. Possesses an
ACTIVE SITE which
reacts with a specific
substrate
10. Able to catalyze
reversible reactions-direction of these
reactions depends
upon substrate
concentrations
Properties/ Characteristics of Enzymes
11. Lower the activation
energy of the
reaction
12. Each has a given
TURN-OVER number
(ex: molecular activity
of catalase is
5.6 x 106 molecules
of H2O2
transformed/minute)
Properties/ Characteristics of Enzymes
13. Some enzymes require COFACTORS
metals essential to the enzymatic
reaction
(ex: catalase requires Fe2+ or Fe3+)
14. Are unaltered by the reaction they
catalyze and thus are REUSABLE
Figure 2-21 Enzyme Action
Enzyme Sucrase In Action
Section 2-4
Enzyme
(hexokinase)
Glucose
Substrates
Products
ADP
Glucose-6phosphate
Products
are released
ATP
Active site
Enzyme-substrate
complex
Substrates
are converted
into products
Substrates
bind to
enzyme
Energy & Living Things
Energy
A. ENERGY: will cause matter to move or change
Ex: mechanical, light, sound, heat, electrical,
nuclear
1. Forms:
1) POTENTIAL (stored)/ ex: sugar cube,
gasoline
- Chemical energy
2) KINETIC (motion)/ ex: heat, light, falling
water (position)
Cont. Energy
2. Thermodynamics: energy conversion/
transformations
1) 1st Law: Energy is not created or destroyedonly changed from one form to another
(converted)
Ex: Food (chemical energy)  Cell work (heat)
2) 2nd Law: Entropy/Disorder- energy is lost to
maintain order and changing trophic levels
Cont. Energy
3. Energy Flow in Ecosystems (Unidirectional)
1)
Sun  Inorganic Chemicals ---- Autotrophs---- Heterotrophs---- Heat
HEAT
(photosynthetic/
HEAT (cellular respiration)
chemosynthetic)
• Open System: Can exchange energy & matter with its
surroundings (Earth)
• Organisms are open systems absorb E (light E/chem E
in form of organic molecules) & releases heat and
metabolic waste products to surroundings
2) Energy in living systems is moved by a transfer of electrons
from one atom to another
Cont. Energy Flow in Ecosystems
3) Reactions that pass electrons are called
OXIDATION-REDUCTION REACTIONS
(Pass e- from one atom to another)
• OXIDATION: removal of electrons (loss) e- or H2
• REDUCTION: addition of electrons (gain) e- or H2
OIL RIG
Becomes oxidized (lose e-)
Na + Cl  Na+ + ClBecomes reduced (gain e-)
Cont. Energy Flow in Ecosystems
4) In chemical reactions, oxidation and
reduction occur simultaneously- if one
molecule gains an electron (reduction), then a
2nd molecule loses the electron (oxidation)
COUPLED REACTION
Cont. Energy Flow in Ecosystems
5) How to determine if organic molecules are
oxidized/reduced:
• REDUCTION: # of C-H bonds increases
• OXIDATION: # of C-H bonds decreases
Ex: Respiration
Becomes oxidized (loses)
C6H12O6 + 6 O2  6 CO2 + 6 H2O + energy
Becomes reduced (gains)
Chemical Reactions
B. CHEMICAL REACTIONS: absorb or release energy
1) Endergonic: needs or uses energy
(energetically unfavorable reaction)
Ex: photosynthesis, building proteins
- Non-spontaneous rxn
2) Exergonic: gives off or releases energy
(energetically favorable reaction)
Ex: respiration, fermentation, burning
- Spontaneous rxn
Figure 2-19 Chemical Reactions
Section 2-4
Chemical Reactions
Endergonic Reaction
Exergonic Reaction
Energy-Absorbing Reaction
Energy-Releasing Reaction
Activation
energy
Products
Activation energy
Reactants
Reactants
Products
Cont. Chemical Reactions
3) The energy that drives reactions is called
free energy reactions releasing free energy
can do cell work
4) Reactions start with reactants and form
products
Cont. Chemical Reactions
5) When fuel (glucose) is oxidized, enzyme
reactions ensure that much of the free energy
released is captured in the form of ATP rather
than being released wastefully as heat to the
environment
6) This is called a coupled reaction energy
released from one reaction can be used to drive a
reaction needing energy/ coupling reactions
requires enzymes and cells conserve energy by
coupling exergonic with endergonic reactions
Cont. Chemical Reactions
7) Enzymes that catalyze cell endergonic
reactions have two active sites:
a. for reactant
b. for ATP
Figure 2-21 Enzyme Action
Section 2-4
Enzyme
(hexokinase)
Glucose
Substrates
Products
ADP
Glucose-6phosphate
Products
are released
ATP
Active site
Enzyme-substrate
complex
Substrates
are converted
into products
Substrates
bind to
enzyme
Coupled Reactions
EXERGONIC
GLUCOSE
ENDERGONIC
C
*ENERGETICALLY FAVORABLE*
- energy released
- can create disorder
ATP
+P
*PRODUCTS HAVE LESS
ENERGY THAN REACTANTS*
*ENERGETICALLY UNFAVORABLE*
- energy needed
- creates order
ADP
D
CO2 + H2O
*PRODUCTS CONTAIN MORE
ENERGY THAN REACTANTS*
Coupled Reactions
C. Coupled reactions form activated/carrier
energy molecule
1) Stores energy in “small packets” easy to
exchange (ATP, NADH, NADPH), which are
specialized to carry electrons and
hydrogen atoms
2) Cells use activated energy carrier
molecules like using money to pay for
reactions
Cont. Coupled Reactions
3) Most important and most abundant
“universal” carrier is ATP
• But NADPH works with enzymes that catalyze
anabolic reactions supplying energy to build
• While NADH works with enzymes that catalyze
catabolic reactions moving energy from food to
make ATP
Cont. Coupled Reactions
4) COENZYMES: organic molecules which
transfer electrons from enzyme to organic
molecule then coenzyme carries electrons to
another enzyme which catalyzes a
different reaction
5) Hydrogen atoms and electrons are stripped
from food and join:
NAD  NADH  makes ATP
Electron Carrier Molecules
Metabolic Pathways
D. METABOLIC PATHWAYS: chains, branching
chains, or cycles
1) A set of enzymes working in a very precise
orderly series of reactions that converts
molecule A into molecule F
Molecule Molecule Molecule Molecule
Molecule Molecule
A

B

C

D

E

F
Enzyme 1 Enzyme 2 Enzyme 3
Enzyme 4 Enzyme 5
Cont. Metabolic Pathways
2) BIOSYNTHETIC PATHWAYS (Anabolic)
• Small building blocks  Complex
macromolecules
Ex: photosynthesis, building proteins)
• Endergonic rxn (“uphill” rxn)
3) DEGREDATIVE PATHWAYS (Catabolic)
• Complex macromolecules Small building blocks
Ex: respiration, fermentation, digestion)
• Exergonic rxn (“downhill” rxn)
Cont. Metabolic Pathways
4) VARIOUS PARTICIPANTS IN THESE PATHWAYS
(Terms)
a)
b)
c)
d)
Substrates: reactants
Intermediates: produced in between
End products: substances remaining at end
Energy carriers: transfers energy (usually
electrons/Hydrogen atoms)
e) Enzymes: catalyze reactions
f) Coenzymes/cofactors: help enzymes & carriers
g) Transport proteins: in membrane/changing
concentrations, influence direction of reaction
Biochemical Pathway: Glycolysis
Cont. Metabolic Pathways
5) Enzymes direct metabolism in cells:
↑ in enzyme concentration causes ↑ in reaction rate
(*to a point, then rate will level)
↑ in substrate concentration causes ↑ in reaction rate
Rxn
Rate
_____________________
ENZYME CONCENTRATION 
Rxn
Rate
Metabolism
E. METABOLISM – Summary
Dehydration synthesis
*building, endergonic
BIOSYNTHESIS
ANABOLISM
-P
MACROMOLECULES
Carbohydrate
Glucose
ADP
ATP
+P
BUILDING BLOCKS
Glucose CHO
CATABOLISM
DEGRADATION
Hydrolysis
*breakdown, exergonic
*ex: cell respiration, fermentation
Cont. Metabolism
1) Built into each living cell are controls over its
enzyme activity
2) By coordinating its control mechanisms, the cell
maintains, increases, or decreases concentrations
of substances– controls can switch on or inhibit
enzymes that are already made
3) ALLOSTERIC CONTROL: enzymes that have
already been formed can be activated or
inactivated when a signal substance combines at
a binding site other than the active site and
causes shape changes to the active site
Cont. Metabolism
4) Biochemical pathways may be controlled by
FEEDBACK INHIBITION: shutting down
of a biochemical pathway due to allosteric
enzyme sensitivity to product concentration
5) ALLOSTERIC ENZYME: enzyme that changes
shape
• has two binding sites 1) active site 2) allosteric site
• signal molecule: binds to enzyme allosteric site
and will activate or deactivate an enzyme
Cont. Allosteric Enzyme
ALLOSTERIC
ENZYME
SIGNAL
------------- ACTIVE (binds to substrate)
MOLECULE
ENZYME
PRESENT
ALLOSTERIC
ENZYME
SIGNAL
-------------
MOLECULE
ABSENT
INACTIVE (cannot bind to
ENZYME
substrate)
Allosteric Enzyme
Cont. Metabolism
6) How a product (concentration) can inactivate an
enzyme that normally makes the product in a
metabolic pathway:
Enzyme A
Enzyme B
Enzyme C
1 -------------- 2 -------------- 3 ------------- 4
• Enzyme A is the allosteric enzyme and has the
allosteric site shape of the product (4), which blocks
substance 1 from beginning the metabolic pathway
• ↑ product concentration ====== Enzyme inactive
(inhibition)
• ↑ product 4 acts as the signal molecule
Feedback Inhibition