Transcript Metabolism PPT - Biology Junction

Introduction to Metabolism
• Metabolism is the sum of an organism’s
chemical reactions
• Metabolism is an emergent property of life
that arises from interactions between
molecules within the cell
A metabolic pathway begins with a specific molecule
and ends with a product
The product of one reaction is substrate of the next
• Each step is catalyzed by a specific enzyme
BIOCHEMICAL PATHWAY
VIDEO
ENZYMES THAT WORK TOGETHER IN A PATHWAY CAN BE
Concentrated
in specific
location
Covalently
bound in
complex
Soluble with
free floating
intermediates
Attached to
a membrane
in sequence
CATABOLIC PATHWAY (CATABOLISM)
Release of energy by the breakdown of
complex molecules to simpler compounds
EX: digestive enzymes break down food
ANABOLIC PATHWAY (ANABOLISM)
consumes energy to build complicated
molecules from simpler ones
EX: linking amino acids to form proteins
Krebs Cycle connects the catabolic and anabolic pathways
Forms of Energy
• ENERGY = capacity to cause change
• Energy exists in various forms
(some of which can perform work)
• Energy can be converted from one form to
another
KINETIC ENERGY –
energy associated with motion
–HEAT (thermal energy) is kinetic energy
associated with random movement of
atoms or molecules
POTENTIAL ENERGY = energy that matter
possesses because of its location or
structure
–CHEMICAL energy is potential energy
available for release in a chemical reaction
On the platform, the diver has
more potential energy.
Climbing up converts kinetic energy
of muscle movement to potential energy.
Diving converts
potential energy to
kinetic energy.
In the water, the diver has
less potential energy.
THERMODYNAMICS
= the study of energy transformations
• CLOSED system (EX: liquid in a thermos)
= isolated from its surroundings
• OPEN system
energy + matter can be transferred
between the system and its surroundings
• Organisms are open systems
The First Law of Thermodynamics
= energy of the universe is constant
– Energy can be transferred and transformed
– Energy cannot be created or destroyed
• The first law is also called the principle of
CONSERVATION OF ENERGY
The Second Law of Thermodynamics
During every energy transfer or transformation
• entropy (disorder) of the universe
INCREASES
• some energy is unusable, often lost as heat
First law of thermodynamics
Chemical
energy
Second law of thermodynamics
Heat
CO2
H2O
ORGANISMS are energy TRANSFORMERS!
Spontaneous processes occur without energy
input; they can happen quickly or slowly
For a process to occur without energy input, it
must increase the entropy of the universe
Free-Energy Change (G) can help tell
which reactions will happen
∆G = change in free energy
∆H = change in total energy (enthalpy) or
change ∆S = entropy
T = temperature
∆G = ∆H - T∆S
• Only processes with a negative ∆G are
spontaneous
• Spontaneous processes can be harnessed to
perform work
Exergonic and Endergonic Reactions in Metabolism
• EXERGONIC reactions
(- ∆G)
• Release energy
• are spontaneous
ENDERGONIC reactions
(+ ∆G)
• Absorb energy from
their surroundings
• are non-spontaneous
Concept 8.3: ATP powers cellular work by coupling
exergonic reactions to endergonic reactions
• A cell does three main kinds of work:
–Mechanical
–Transport
–Chemical
• In the cell, the energy from the exergonic
reaction of ATP hydrolysis can be used to
drive an endergonic reaction
• Overall, the coupled reactions are exergonic
ATP (adenosine triphosphate) is the cell’s renewable
and reusable energy shuttle
ATP provides energy for cellular functions
Energy to charge ATP comes from catabolic reactions
Adenine
Phosphate groups
Ribose
P
P
P
Adenosine triphosphate (ATP)
H2O
Pi
+
Inorganic phosphate
P
P
Adenosine diphosphate (ADP)
+
Energy
ATP
Energy for cellular work
provided by the loss of
phosphate from ATP
Energy from catabolism
(used to charge up
ADP into ATP
ADP +
P
i
Endergonic reaction:
DG is positive, reaction is not spontaneous
NH2
Glu
+
NH3
Ammonia
Glutamic
acid
G = +3.4 kcal/mol
Glu
Glutamine
Exergonic reaction:
DG is negative, reaction is spontaneous
ATP
+
H2O
Coupled reactions:
Overall DG is negative;
Together, reactions are spontaneous
ADP
+
P i
G = –7.3 kcal/mol
G = –3.9 kcal/mol
Pi
P
Motor protein
Protein moved
Mechanical work: ATP phosphorylates motor proteins
Membrane
protein
ADP
+
Pi
ATP
Pi
P
Solute transported
Solute
Transport work: ATP phosphorylates transport proteins
P
Glu
+
NH3
Reactants: Glutamic acid
and ammonia
NH2
Glu
+
Pi
Product (glutamine)
made
Chemical work: ATP phosphorylates key reactants
Every chemical reaction between molecules involves
bond breaking and bond forming
ACTIVATION ENERGY =
amount of energy required to get chemical reaction started
Activation energy is often supplied in the form
of heat from the surroundings
Free energy animation
IT’S LIKE PUSHING A
SNOWBALL UP A HILL . . .
Once you get it up there,
it can roll down by itself
The Activation Energy Barrier
A
B
C
D
Free energy
Transition state
A
B
C
D
EA
Reactants
A
B
G < O
C
D
Products
Progress of the reaction
CATALYST = a chemical agent that speeds up
a reaction without being consumed by the
reaction
ENZYMES = biological catalysts
Most enzymes are PROTEINS
Exception = ribozymes (RNA)
Free energy
Course of
reaction
without
enzyme
EA
without
enzyme
EA with
enzyme
is lower
Reactants
Course of
reaction
with enzyme
G is unaffected
by enzyme
Products
Progress of the reaction
ENZYMES work by LOWERING ACTIVATION ENERGY;
ENZYMES LOWER ACTIVATION ENERGY BY:
–Orienting substrates correctly
–Straining substrate bonds
–Providing a favorable microenvironment
Enzymes change
ACTIVATION ENERGY
but NOT energy of
REACTANTS or PRODUCTS
ENZYMES
•
•
•
•
•
•
Most are proteins
Lower activation energy
Specific
Shape determines function
Re-usable
Unchanged by reaction
• The REACTANT that an enzyme acts on
= SUBSTRATE
• Enzyme + substrate =
ENZYME-SUBSTRATE COMPLEX
• Region on the enzyme where the substrate
binds = ACTIVE SITE
• Substrate held in active site by WEAK
interactions (ie. hydrogen and ionic bonds)
TWO MODELS PROPOSED
• LOCK & KEY
Active site on enzyme
fits substrate exactly
• INDUCED FIT
Binding of substrate causes change
in active site so it fits substrate
more closely
Enzyme Activity can be affected by:
–General environmental factors, such
as temperature, pH, salt
concentration, etc.
–Chemicals that specifically influence
the enzyme
See a movie
Choose narrated
TEMPERATURE & ENZYME ACTIVITY
Each enzyme has an optimal temperature at which
it can function (Usually near body temp)
Increasing temperature increases the rate of an
enzyme-catalyzed reaction up to a point.
Above a certain temperature, activity begins to
decline because the enzyme begins to denature.
pH and ENZYME ACTIVITY
Each enzyme has an optimal pH at which it can
function
COFACTORS
= non-protein enzyme helpers
•
EX: Zinc, iron, copper
COENZYMES
= organic enzyme helpers
• Ex: vitamins
SUBSTRATE CONCENTRATION
& ENZYME ACTIVITY
← V
MAX
Adding substrate increases activity up to a point
REGULATION OF ENZYME PATHWAYS
• GENE REGULATION
cell switches on or off the genes that code
for specific enzymes
REGULATION OF ENZYME PATHWAYS
• FEEDBACK INHIBITION
end product of a pathway interacts with and
“turns off” an enzyme earlier in pathway
FEEDBACK INHIBITION
• prevents a cell from wasting chemical
resources by synthesizing more product than
is needed
NEGATIVE FEEDBACK
– An accumulation of an end product slows the process
that produces that product
A
Negative
feedback
Enzyme 1
B
A
Enzyme 1
B
Enzyme 2
C
C
Enzyme 3
D
D
D
D
D
D
D
D
D
D
D
Example: sugar breakdown generates ATP; excess ATP
inhibits an enzyme near the beginning of the pathway
POSITIVE FEEDBACK (less common)
–The end product speeds up production
W
W
Enzyme 4
Enzyme 4
Positive
feedback
X
X
Enzyme 5
Enzyme 5
Y
Y
Enzyme 6
Z
Enzyme 6
Z
Z
Z
Z
Z
Z
Z
Z
Z
Z
Z
Z
Z
Z
Z
Z
Z
Z
EXAMPLE: Chemicals released by platelets that accumulate
at injury site, attract MORE platelets to the site.
REGULATION OF ENZYME ACTIVITY
• ALLOSTERIC REGULATION
protein’s function at one site is affected by
binding of a regulatory molecule at another
site
• Allosteric regulation can inhibit or stimulate
an enzyme’s activity
Allosteric enzyme
inhibition
SOME ALLOSTERIC ENZYMES HAVE
MULTIPLE SUBUNITS
• Each enzyme has active and inactive forms
• The binding of an
ACTIVATOR stabilizes
the active form
• The binding of an
INHIBITOR stabilizes
the inactive form
Binding of one substrate molecule to
active site of one subunit locks all
subunits in active conformation.
Substrate
Inactive form
Stabilized active form
COOPERATIVITY another type of allosteric activation
COOPERATIVITY
= form of allosteric regulation that can amplify
enzyme activity
Binding of one substrate to active site of one
subunit locks all subunits in active conformation
Enzyme Inhibitors
COMPETITIVE inhibitor
REVERSIBLE; Mimics substrate and
competes with substrate for active site on
enzyme
ENZYME
ANIMATION
Enzyme Inhibitors
NONCOMPETITIVE inhibitors bind to another
part of an enzyme, causing the enzyme to
change shape and making the active site less
effective
ENZYME
ANIMATION