Download Introduction to Metabolism

Introduction to Metabolism
Ch. 8 – AP Biology
Metabolism
•Definition – The
totality of an
organism’s chemical
processes
•An organism’s
chemical reactions are
arranged into
intricately branched
pathways
–Metabolic pathway
•Alters molecules by a
series of steps.
•Each step is
selectively
accelerated by a
particular enzyme
Catabolic Pathways
• Result in the breakdown of complex
molecules into simpler compounds.
• Example: Cellular respiration
– Glucose is broken down into CO2 and H2O
– Energy that was stored in the chemical
bonds of glucose becomes available to do
work for the cell.
Anabolic Pathways
• Pathways that consume energy to
build complicated molecules from
simpler molecules
• Example: making proteins from amino
acids
• Example: Photosynthesis
Organisms are Energy Transformers
•Energy
–The ability to do work.
•Two Types of Energy
–Kinetic
•Energy of motion
•Example: light
–Potential
•Stored energy
•Possessed by matter
because of its location or
structure
•Chemical energy –
especially important in
biology
•Transformation of energy
from kinetic to potential
and back again is essential
to life.
–Living things do this all
the time!
Thermodynamics
• The study of energy transformations
• Organisms are open systems
– They absorb energy from the environment
– They release heat into the environment
Laws of Thermodynamics
• 1st Law of Thermodynamics
– Energy can be transformed, but it cannot be
created or destroyed
• 2nd Law of Thermodynamics
– Energy transformation increases the entropy of the
universe
– Entropy = measure of disorder or randomness
– Example of entropy: heat
– In most energy transformations, ORDERED forms
of energy are converted to HEAT
• Conversion of energy to different forms does
NOT violate 1st law.
• Order of life does NOT violate the 2nd Law.
– Entropy of the UNIVERSE, as a whole, is increasing
in spite of the order that living things maintain…at
least for a while.
– QUANTITY of energy in the universe is constant;
– QUALITY of energy is not.
Free Energy
•Spontaneous change
–Change that can occur
without outside help
–Can be harnessed to
perform work
–Causes stability of a
system to increase
•Unstable systems
tend to change to
become more stable
–A process can occur
spontaneously ONLY if
it increases the entropy
of the universe.
Free Energy
• Definition
– Portion of a system’s energy that can
perform work when temperatures are
uniform in the system
• Symbol
–G
Concept of Free Energy helps us determine if a process can
occur spontaneously.
• G is a measure of a system’s instability
– It’s tendency to change to move to a more stable
state.
• Systems that are rich in energy are unstable
• More complex molecules are rich in energy
and therefore, unstable.
• Those systems that tend to change
spontaneously to a more stable state are
those that have high energy and thus low
entropy.
• In any spontaneous process, the G of a
system DECREASES
– Change in G would be negative.
Free Energy and Chemical Reactions
• As a chemical reaction moves toward
equilibrium, free energy of the reactants and
products decreases.
• Free energy INCREASES when the reaction is
moved away from equilibrium.
• At equilibrium, change in G = 0
• At equilibrium, a chemical reaction performs
NO work.
• A process is spontaneous and CAN perform
work when it is SLIDING TOWARD
equilibrium
• Movement AWAY from equilibrium is
NONspontaneous and occurs ONLY with the
help of an OUTSIDE ENERGY source.
Exergonic Reactions
•Energy
outward
•Proceeds
with a net
release of free
energy
•Change in G
is negative
•CELLULAR
RESPIRATION
Endergonic Reaction
•Energy inward
•STORES free energy
in molecules
•Change in G is
positive
•NONspontaneous
•PHOTOSYNTHESIS
•If a chemical
process is
EXERGONIC in one
direction, it must be
ENDERGONIC in the
reverse direction.
Cells at equilibrium…
• Are DEAD.
• Thus, it is advantageous to sustain
DISequilibrium
– Product of one reaction is not allowed to
accumulate, but instead becomes a
reactant in the next step along some
metabolic pathway.
ATP and Cellular Work
• Cells do three kinds of work
– Mechanical
• Moving stuff – cilia for example
– Transport
• Moving molecules against concentration
gradient
– Chemical
• Pushing of reactions that would NOT occur
spontaneously
• ATP is the immediate source of energy
that powers cellular work
ATP
• Adenosine Triphosphate
Hydrolysis of ATP
• Breaking of bonds between the phosphate
groups of the ATP “tail”
• Energy is released
• Molecules of ADP and Pi (inorganic
phosphate) are left behind
• EXERGONIC
• Change in G is – 7.3 Kcal/mol
• Phosphate bonds are NOT unusually strong –
in fact, they are fragile
– All 3 phosphate groups are negatively charged
– Triphosphate tail is like a loaded spring
• ADP and Pi are more stable than ATP
ADP and Pi are Renewable
• ATP is made from the ADP and Pi that
result when ATP is used by the cell
• If ATP were NOT recyclable in this
way, humans would have to consume
their body weight in ATP each day.
• The regeneration of ATP from ADP and
Pi is endergonic
– +7.3 kcal/mol are required
• Cellular Respiration is the process that
makes the energy to regenerate ATP
– Energy is RELEASED from the breakdown
of a GLUCOSE molecule to do this
ATP and Pi are Renewable
ENZYMES
• Just because a reaction is
spontaneous, does NOT mean it is fast.
– Many chemical reactions happen so slowly
that they are imperceptible.
• Enzymes are CATALYSTS.
– Speeds the rate of a chemical reaction
without being consumed in the reaction
Activation Energy
• Initial energy required to get a reaction
started
– Initial energy required to break bonds
– Acts as a barrier that must be overcome in order for
the reaction to occur
– Someone has to push the boulder off the top of the
mountain in order for it to fall.
• Heat is one way to provide activation energy
– Speed up movement of molecules
– Increase collisions; stress bonds
– However, heat is BAD for cells
• Enzymes LOWER activation energy without
increasing temperature
Activation Energy
ENZYMES
• Substrate – substance upon which the
enzyme acts
• The substrate will undergo change to
become product
• The enzyme remains unchanged
– Can be used again and again
Fit of Enzymes with Substrates
•Enzymes are
complexly shaped
–Active site
•Region of enzyme
that interacts with
substrate
•Shape of active
site is critical to
function
•Induced fit
–Enzyme fits
substrate like a
clasping handshake
•Enzyme is induced
by substrate to
change its shape to
fit the substrate
precisely/snugly
–Not rigid like a key
and lock
Enzyme Action
• Enzyme-substrate complex forms
• Substrate is held at the active site by
– hydrogen bonds; ionic bonds, etc.
• Induced fit between enzyme and substrate occurs
• Enzymes catalyze reactions in a variety of ways
– Stress bonds of substrate making them easier to
break
– Bringing two or more substrates together making it
more likely they will bond
• Enzyme releases products
– Enzyme will go on to act again and again
– 1000 molecules/sec!
• An enzyme is saturated when it is catalyzing the
maximum number of reactions it can
– Only way to speed reaction would be to add more
enzyme
Enzyme Action
Affects of Environment on Enzymes
• Denature – enzyme loses its shape
– Shape is CRITICAL to function
– If misshapen, the enzyme will not work
• Factors that denature enzymes
– Increase in Temperatures
– pH
– There are others….
• Other environmental factors may not
denature enzymes, but still affect their ability
to catalzye
– Decrease in Temperature
• Lowers speed of molecules
• Lowers number of collisions
• Lowers rate of reaction
Cofactors
• Nonprotein “helpers” of enzymes
– Molecules that help enzymes do their jobs
– Inorganic
• Metal atoms – zinc, copper, iron
– Organic
• Coenzymes - vitamins
Enzyme Inhibitors
•A chemical that
specifically and
selectively inhibits a
particular enzyme
•Helps control enzyme
activity
CONTROL OF METABOLISM
• Metaboic Pathways
– Also called biochemical pathways
– The product of one reaction becomes the
reactant for the next reaction until the
needed product is made
– Many steps
– Each step is catalyzed by a particular
enzyme
• These pathways can be controlled by
– Switching on and off the genes that
encode specific enzymes (genetic control)
– Regulating the activity of enzymes once
they are made (focus of our study now)
Allosteric Enzymes
•Enzyme has two
active sites
–“normal” active
site that
interacts with
substrate
–2nd active site
(or receptor
region) that
binds with some
molecule that
affects activity of
the enzyme
itself.
•2nd site may be used
to inhibit or stimulate
an enzyme’s activity
Feedback Inhibition
•End product of a
biochemical pathway
acts as inhibitor of an
enzyme within the
pathway
•Switches OFF the
metabolic pathway
•Prevents the cell from
wasting chemical
resources if the
product of the
pathway is already in
good supply
Cooperativity
•Enzymes can also be
stimulated to go to
work
•Cooperativity
amplifies the response
of an enzyme to its
substrate
Organelles help to ORDER metabolism
•Enzymes are often
isolated from different
parts of the cell by the
organelles that
contain them
–Helps control
sequence of chemical
reactions
–Keeps incompatible
processes separated
–Allows for more
efficient reaction
results