An Introduction to Metabolism. Metabolism = Catabolism + Anabolism Catabolic reactions are energy...
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Transcript of An Introduction to Metabolism. Metabolism = Catabolism + Anabolism Catabolic reactions are energy...
Metabolism = Catabolism + Anabolism
Catabolic reactions are energy yielding
•They are involved in the breakdown of more-complex molecules into simpler ones
Anabolic reactions are energy requiring
•They are involved in the building up of simpler molecules into more-complex ones
Introduction to Metabolism
“Energy can be transferred or
transformed but neither created nor destroyed.”
“Every energy transfer or transformation increases the
disorder (entropy) of the universe.”
Note especially the waste heat
First and Second Laws of ThermodynamicsFirst and Second Laws of Thermodynamics
Organisms take in energy & transduce it to new forms (1st law)
As energy transducers, organisms are less than 100% efficient (2nd law)
Organisms employ this energy to:• Grow• Protect Themselves• Repair Themselves• Compete with other Organisms• Make new Organisms (I.e., babies) In the process, organisms generate waste
chemicals & heat Organisms create local regions of order at
the expense of the total energy found in the Universe!!! We are Energy Parasites!
Energy in the Biosphere
First Law of Thermodynamics:
•Energy can be neither created nor destroyed
•Therefore, energy “generated” in any system is energy that has been transformed from one state to another (e.g., chemically stored energy transformed to heat)
Second Law of Thermodynamics:
•Efficiencies of energy transformation never equal 100%
•Therefore, all processes lose energy, typically as heat, and are not reversible unless the system is open & the lost energy is resupplied from the environment
•Conversion to heat is the ultimate fate of chemical energy
Note that “Spontaneity” is not a measure of speed of a
process, only its direction
Movement towards Equilibrium in Movement towards Equilibrium in StepsSteps
Exergonic Reaction (Spontaneous)Exergonic Reaction (Spontaneous)• Decrease in Gibbs free energy (-G)• Increase in stability• Spontaneous (gives off net energy upon going forward)• Downhill (toward center of gravity well, e.g., of Earth)• Movement towards equilibrium• Coupled to ATP production (ADP phosphorylation)• Catabolism
Endergonic Reaction (Non-Spontaneous)• Increase in Gibbs free energy (+G)• Decrease in stability• Not Spontaneous (requires net input of energy to go forward)• Uphill (away from center of gravity well, e.g., of Earth)• Movement away from equilibrium• Coupled to ATP utilization (ATP dephosphorylation)• Anabolism
Cou
plin
g R
eact
ions
Cou
plin
g R
eact
ions
Exergonic reactions can supply energy for endergonic
reactions
Ene
rgy
Cou
plin
g in
Met
abol
ism
Ene
rgy
Cou
plin
g in
Met
abol
ism
Catabolic reaction
Anabolic reaction
Catabolic reactions provide the energy that drives anabolic reactions forward
Summary of Metabolic Summary of Metabolic CouplingCoupling
Endergonic reaction
Exergonic reaction
Exergonic reaction
Endergonic reaction
Exergonic processes drive Endergonic processes
Enzyme Catalyzed Enzyme Catalyzed ReactionReaction
Question: Is this reaction
endergonic or is it exergonic?
Enzyme
Act
ivat
ion
Ene
rgy
(EA
ctiv
atio
n E
nerg
y (E
AA)) Anything that
doesn’t require an input of
energy to get started has
already happened!
Low
- (i.
e., b
ody-
) T
emp.
Sta
bilit
yLo
w-
(i.e.
, bod
y-)
Tem
p. S
tabi
lity
Why don't energy-rich molecules, e.g., glucose, spontaneously degrade into CO2 and Water?
• To be unstable, something must have the potential to change into something else, typically something that possesses less free energy
• To be unstable, releasing something’s ability to change into something else must also be relatively easy (i.e., little input energy)
• Therefore, stability = already low free energy
• Alternatively, stability = high activation energy
Things, therefore, can be high in free energy but still quite stable, e.g., glucose
CatalysisCatalysis
At a given temperature,
catalyzed reactions can run faster
because less energy is required to achieve
the transition state
This is instead of adding heat; heat is an inefficient means
of speeding up reactions since it
simply is a means of increasing the
random jostlings of molecules
Mec
hani
sms
of
Mec
hani
sms
of
Cat
alys
isC
atal
ysis
Active sites can hold two or more substrates in proper orientations so that new bonds between substrates can form
Active sites can stress the substrate into the transition state
Active sites can maintain conducive physical environments (e.g., pH)
Active sites can participate directly in the reaction (e.g., forming transient covalent bonds with substrates)
Active sites can carry out a sequence of manipulations in a defined temporal order (e.g., step A step B step C)
Catalysis as Viewed in 3DCatalysis as Viewed in 3D
Active site is site of
catalysis
The rest of an enzyme is involved in
supporting active site, controlling reaction rates,
attaching to other things, etc.
Indu
ced
Fit
(Act
ive
Indu
ced
Fit
(Act
ive
Site
)S
ite)
Induced fit not only allows the enzyme to bind the substrate(s), but also provides a subtle application of energy (e.g., “bending” chemical bonds) that causes the substrate(s) to destabilize into the transition state
Enz
yme
Sat
urat
ion
Enz
yme
Sat
urat
ion Substr
ateProduct
Enzyme Activity at Saturation is a Function of Enzyme Turnover Rate
Non-Specific Inhibition of Enzyme Non-Specific Inhibition of Enzyme ActivityActivity
Instability & shape change
(too fluid)
Reduced rate of chemical
reaction
Reduced enzyme fluidity
Change in R group
ionization
Change in R group
ionization
Denatured?
Turnover rate
Even at saturation, rates of enzymatic reactions
can be modified
Spe
cific
S
peci
fic
Inhi
bitio
nIn
hibi
tion
Competitive inhibitors can be competed
off by supplying sufficient substrate densities
Non-competitive inhibitors cannot be competed off
by substrate
Allo
ster
ic
Allo
ster
ic
Inte
ract
ions
Inte
ract
ions
Reversible interactions,
sometimes on, sometimes off, dependent on
binding constant and
density of effector
CooperativityCooperativityCooperativity is when the activity of
other subunits are increased by
substrate binding to
one subunit’s active site
Enz
yme
Loca
lizat
ion
Enz
yme
Loca
lizat
ion
Organization of Electron
Transport Chain of Cellular
Respiration
Enzymes in single pathway may be co-localized so that the product of one enzyme
increases the local concentration of the substrate for another