Cells build up and breakdown molecules
in steps.
Each step is helped along by enzymes
Structure: Enzymes are proteins
• Made of
amino acids
• Peptide
bonds
Review
Protein
Structure
The chemistry of life is organized into
metabolic pathways
• The totality of an organism’s chemical reactions
is called metabolism.
• A cell’s metabolism is an elaborate road map of
the chemical
reactions in that cell.
• Metabolic pathways alter
molecules in a series of steps.
• Enzymes selectively
accelerate each step.
• The activity is regulated to
maintain an appropriate balance
of supply and demand.
• Catabolic pathways release energy by
breaking down complex molecules to simpler
compounds.
• This energy can be stored for later use.
• Ex. Cellular respiration
• Anabolic pathways consume energy to build
complicated molecules from simpler compounds.
• Ex. Protein
synthesis
• The principles that govern energy resources in
chemistry and physics also apply to bioenergetics,
the study of how organisms manage their energy
resources.
*these pathways intersect in such a
way that the energy released from
Cat. can be used to drive Anab. –
transfer of energy is called
Energy coupling
(ATP very important…transfer energy from one reaction to another)
• Living systems transform one form
of energy to another in order to
carry out essential life functions.
• The laws of thermodynamics govern
these energy transformations.
Physical Science review:


Energy
Defined as capacity to do work (move
matter against opposing forces)
Exists in a variety of forms, and work of life
depends on ability of cells to transform
energy from one type into another
Potential vs. Kinetic

Potential energy:
stored energy that
matter possesses
because of its location or
structure (Bio-chem pot E)
Ex. Chemical energy in organic
molecules, water in reservoir
behind dam

Kinetic energy: energy
of motion
Ex. Water gushing through
dam, light energy, heat energy
Laws of thermodynamics
• 1st-energy cannot be created or
destroyed, only transferred/
transformed.
– Also known as conservation of energy
law.
•2nd-in the course of energy conversions, the
universe become more disordered (greater
entropy).
•Every energy transfer or transformation
makes the universe more disordered.
Gibb’s free energy equation
ΔG = Δ H –T Δ S
• Important to understanding metabolism.
• Can predict which process/reactions can
supply energy to do work.
Free energy: Portion of a system’s energy
that can be used to perform work.
(Is “free” b/c is available for work, not because it
does not cost the universe something…)
Guest Speaker: MR. ANDERSDON……
What is FREE ENERGY?????
Answer
• The measure of the disorder or randomness
ΔG = Δ H –T Δ S
•
•
•
•
G = free energy change
ΔH=Change in heat content (enthalpy)
T= absolute temperature
ΔS= systems Entropy
Once we know the value of “G” for a process,
we can use it to predict whether it is
ATP  ADP
exergonic or endergonic.
DG = -30.5 kJ
-G: releasing energy (exergonic/exothermic)
o
 Spontaneous- (must give up heat or order)
 Decreases the free energy
+G: absorbing energy (endergonic/endothermic)
(or zero)
1878-Willard Gibbs
Free energy: Portion of a system’s energy that can perform work when temp &
pressure are uniform throughout the system.
(Is “free” b/c is available for work, not because it does not cost the universe
something…)
Exergonic – energy outward; proceed with a net
release of free energy -usually releases energy in
form of heat; these rxns occur spontaneously (ΔG is
negative)
Clip
Endergonic – energy inward; absorbs free energy
from its surroundings, containers for these rxns
tend to feel cool (ΔG is positive)
Function:
• Enzymes
speed up
chemical
reaction by
lowering
the
activation
energy
(amount of
energy
needed to
start the
rxn).
•Potential Energy of products is less that Potential
Energy of reactants, so energy is releasedexothermic.
•---line shows same rxn w/enzyme.
•Rxn can proceed more quickly.
•Potential Energy of products is more that
Potential Energy of reactants, so energy is
absorbed-endothermic.
•---line shows same rxn w/enzyme.
•Rxn can proceed more quickly.
Stop here
• Do the 4 activities in Ch 8
• Take the “activities quiz”
• Online; Phschool.com : AP Lab #2
– Go through the background info
– Skip experiment
– Take quiz
• Tonight:
– Read pages 141-157
• Take your own notes
– Read Lab background information.
How do they work:
Enzymes
• In simple terms, an
enzyme functions by
binding to one or more
of the reactants in a
reaction.
• The reactants that bind
to the enzyme are
known as the substrates
of the enzyme.
•The exact location on the enzyme where
substrate binding takes place is called the
active site of the enzyme.
Binding
Specificity
Enzymes can
only bind to
certain
molecules
The shape of the active site just fits the
shape of the substrate, somewhat like a lock
fits a key. In this way only the correct
substrate binds to the enzyme.
CLIP
Clip 2
• Induced fit modelthe substrate
induces the enzyme
to change its shape.
•Once the enzymesubstrate complex is
together, the enzyme
holds the substrate in a
position where the
reaction can occur.
•Weak bonds form
between the substrate
and the amino acids in
the active site.
•Enzymes are not used up
in the reaction
Example of an enzyme-catalyzed reaction: Hydrolysis of sucrose
A solution of sucrose dissolved in sterile water will sit for
years at room temp with no appreciable hydrolysis
occurring….BUT, if add SUCRASE (an enzyme), the sucrose
will be converted in seconds…
Functions:
All enzymes have four special features in common:
1.They do not make processes happen that would
not take place on their own. They just make the
processes take place faster!
2. Enzymes are not permanently altered or used up
in reactions.
4 Each enzyme is highly selective about its
substrate.
Control, regulation and
other points of
Metabolism
Enzymes: Control
Physical and Chemical Environment
affects Enzyme Activity…
1. Temperature – too high, denatures protein
2. Concentration of enzyme and substrate3. pH – too high or too low, denatures protein
4. Cofactors – inorganic (elemental) nonprotein helper
bound to active site; must be present for some
Clip;
enzymes to function (zinc, iron, copper)
Coenzymes
5. Coenzymes – organic nonprotein helper bound to
active site; again, must be present (vitamins)required for enzymes to work
-make up a part of the active site --without the
coenzyme, the enzyme will not function.
How fast or slow the enzyme works depends on:
1. The concentration of the enzyme
All necessary cofactors (inorganic molecules) and coenzymes (vitamins)
are present above.
1. Presence of excess substrate, the reaction rate increases in
direct proportion to the [enzyme].
2.Rate increases until reaches max velocity.
How fast or slow the enzyme works depends on
1.the concentration of the enzyme. If the
enzyme is diluted, its concentration is lowered,
which slows the reaction rate.
• If the enzyme concentration remains constant as the substrate
concentration increases, the rate of the reaction increases until
the rate of reaction approaches the maximum velocity.
• From this point on the enzyme is saturated and the rate
of reaction can no longer increase.
How fast or slow the enzyme works depends on
2. pH
-different enzymes
have different
optimal pHs
3. Temperature
-body temp
ph can affect
enzyme activity.
Control of Metabolism
• Cell regulates metabolic pathways by
controlling when and where
enzymes are active
• Does this by
*switching on or off the genes for
production of specific enzymes
OR
*regulating enzymes after they are
made
2 types
Enzyme Inhibitors
1. Competitive
blocks active site,
mimics substrate
2. Noncompetitive bind to another
part of enzyme and change
shape of enzyme – can’t work on
substrate
Competitive
Inhibition
• Molecules that
resemble the substrate
compete for the active
site.
• Reduce the productivity
of the enzyme by
preventing the
substrate from
combining w/the
enzyme.
• Inhibitors can be
reversible or
irreversible.
Animation
Noncompetitive Inhibition
• Enzyme contains more than 1 active site and
the substrates do not resemble each other.
• When one substrate binds to an active site,
the second site is blocked.
• Binding is random and a function of the
concentration of each substrate.
Allosteric Inhibition
(type of Noncompetitive)
• Two active sites, one for the
substrate and one for an
inhibitor (or enhancer).
Usually reversiable.
EX: Feedback inhibition during
glycolysis.
-ATP inhibits the enzyme PFK
which catalyzes step 3. A
metabolic pathway is
switched off by its end
product. Prevents the cell
from wasting energy.
Clip
Clip 2 with Quiz
Allosteric regulation of enzyme activity
*By binding to allosteric site, can either inhibit or
stimulate
*Most allosterically regulated enzymes are made up
of one or more polypeptide subunits
Negative
Feedback
Inhibition:
Swiching off
of a
metabolic
pathway by
its end
product,
which acts an
an inhibitor
of an enzyme
within the
pathway.
PFK is also an example
• Positive Feedback:
– The product of one or a series of
enzymatic reactions acts upon the
enzymes responsible for the generation
of that product to increase the activity
of one or more of these enzymes.
Childbirth: The hormone oxytocin
stimulates and enhances labor
contractions. As the baby moves
toward the birth canal, pressure
receptors within the cervix send
messages to the brain to produce
oxytocin. Oxytocin travels to the
uterus through the bloodstream,
stimulating the muscles in the uterine
wall to contract stronger. More
pressure…more oxytocin is produced
until the baby is outside the birth
canal.
Your stomach normally secretes a
compound called pepsinogen that is an
inactive enzyme. As your body converts
pepsinogen to the enzyme pepsin, it
triggers a process that helps convert
other pepsinogen molecules to pepsin.
This cascade effect occurs and soon
your stomach has enough pepsin
molecules to digest proteins
Review:
• Mr. Anderson’s “Enzymes” review
• http://www.stolaf.edu/people/giannini/biolo
gical%20anamations.html