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3/22/2016
Metabolism
INTRODUCTION TO
METABOLISM
• ALL the chemical
reactions in an organism
• Chemical reactions of life
– forming bonds
between molecules
• dehydration synthesis
• synthesis
• anabolic reactions
– breaking bonds
between molecules
• hydrolysis
• digestion
• catabolic reactions
Catabolic Pathways
• Catabolism
–Release of energy
by the breakdown
of complex
molecules to
simpler
compounds
–Breaking!!
• Ex. Digestive
enzymes
breakdown food
Organisms Transform Energy
• Energy
Anabolic Pathways
• Anabolism
–Consumes energy
to build
complicated
molecules from
simpler ones
• Ex. Linking
amino acids to
form proteins
Laws of Thermodynamics
• Thermodynamics
– The capacity to do work
– Study of energy transformations that occur in matter
– Kinetic (motion)
– Potential (gravitational)
– Thermal (heat)
– Nuclear
– Radiative (light)
– 1st law of thermodynamics
• Conservation of energy
• Energy of the universe is constant.
• Energy CAN BE transferred and transformed, but NEVER
created nor destroyed
– 2nd law of thermodynamics
• Every energy transfer or transformation increases the
entropy (disorder or randomness) in universe
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Energy of System
Energy in Reactions
• Exergonic reaction
• Equation
– Releases energy
– Occurs spontaneously
– Energy of products is LOWER than
energy of reactants (negative G)
G = ∆H - T∆S
S = Entropy
 G = Free Energy of a system
• Endergonic reaction
– Requires energy; absorbs free
energy from the system
– Non-spontaneous
– Energy of products is HIGHER than
energy of reactants
Energy that is able to work when the temperature is
uniform
Change in free energy is represented by ∆G
 H = Total energy in the system
 T = Absolute temperature in Kelvin
• Spontaneous reaction
– Can occur without outside help
– Can be harnessed to do work
(objects moving down their power
gradient)
Endergonic vs. exergonic
reactions
exergonic
endergonic
- energy released
- digestion
- energy invested
- synthesis
The Energy of Life
• Organisms are endergonic
systems
– What do we need energy for?
• synthesis
– building biomolecules
+G
-G
•
•
•
•
reproduction
movement
active transport
temperature regulation
G = change in free energy = ability to do work
Where do we get the
energy from?
• Work of life is done by energy coupling
– use exergonic (catabolic) reactions to fuel
endergonic (anabolic) reactions
DIGESTION
+
SYNTHESIS
+
+
energy
+
energy
Living Economy
• Fueling the body’s economy
– eat high energy organic molecules
• food = carbohydrates, lipids, proteins, nucleic acids
– break them down
• digest = catabolism
– capture released energy in a form the cell can
use
• Need an energy currency
– a way to pass energy around
– need a short term energy
storage molecule
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ATP
How does ATP store energy?
• Adenosine Tri-Phosphate
• Each negative PO4 more difficult to add
– a lot of stored energy in each bond
– modified nucleotide
• most energy stored in 3rd Pi
• 3rd Pi is hardest group to keep bonded to molecule
• nucleotide =
adenine + ribose + Pi  AMP
• AMP + Pi  ADP
• ADP + Pi  ATP
– adding phosphates is endergonic
– Primary energy source in cells
• Bonding of negative Pi groups is unstable
– spring-loaded
– Pi groups “pop” off easily & release energy
• Instability of its P bonds makes ATP an excellent
energy donor
How does ATP transfer
energy?
ATP/ADP Cycle
• ATP  ADP
– releases energy
• Can’t store ATP
• ATP is a good energy donor,
but NOT a good energy storage molecule
• ∆G = -7.3 kcal/mole
• Fuel other reactions
• Phosphorylation
– released Pi can transfer to
other molecules
• too reactive
• transfers Pi too easily
• only short term energy storage
– carbohydrates & fats are long term energy
storage
• Cells spend a lot of time making ATP
• destabilizing the other
molecules
– enzyme that
phosphorylates = “kinase”
ATP synthase
H+
H+
• Enzyme channel in
mitochondrial membrane
– permeable to H+
– H+ flow down
concentration gradient
• flow like water over
water wheel
• flowing H+ cause
change in shape of ADP
ATP synthase enzyme
• powers bonding of
Pi to ADP:
ADP + Pi  ATP
H+
H+
H+
H+
H+
H+
rotor
rod
catalytic
head
+ P
ATP
H+
But… HOW is the proton (H+) gradient formed?
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