The Design of Metabolism
key concepts*
or How Biological Order
Comes About...
METABOLISM....
the catalytic reactions (run by enzymes) of cells.....
metabolic pathways [A --> B
--> C --> D
--> E]
- 2 Categories catalytic reactions -
-
CATABOLISM...
chemical oxidation of food
stuffs or
Cell Respiration
1) digestion of polymers (foods) [hydrolysis
reactions] to glucose
2) GLYCO-LYSIS glucose ---> pyruvate [splitting of sugar]
3) KREBS cycle
oxidation of Acetyl-CoA ---> CO2 +
NADH ----> H2O
-
4) ELECTRON TRANSFER ----> NADH + O2 ---->
H2O + H+ gradient
5) ATP SYNTHASE
---> use a H+ gradient to phosphorylate P + ADP
----> ATP
5 steps*
ANABOLISM...
Biosynthesis, often via...
coupled reactions - energetically unfavored w favored
reactions
1)
PHOTOSYNTHESIS reduction of CO2
to CH2O
-
-
-
ENERGY
(transformations)
energy is capacity or ability to do work
kinds: KINETIC -
energy of motion motion
POTENTIAL - stored energy; capacity to do work (eventually);
HEAT - assoc with movement of molecules in a body of matter;
most random form of energy (wasted).
Student Media Activities -
chapter 6A -
Energy Transformations |
 |
-
EXAMPLES
general: heat, light, sound, mechanical
of energy:
biological: synthetic, osmotic, mechanical,
-
-
molecules in
living cells have chemical potential energy to do work...
- because of the arrangement (orientation) of their atoms
- in space... we call this
CHEMICAL BIOND ENERGY
&
-
the energy of cells is stored in the COVALENT BONDS of their molecules.
HOMEOSTASIS ...most of cell's energy is needed to maintain
a steady state.
-
BIOENERGETICS
- is study of energy transformations (changes) in Biological systems is based on
EQUILIBRIUM THERMODYNAMICS...
-
1st LAW = Conservation of Energy...
energy is a constant;
energy can not be created
nor destroyed, only transformed
... experimental caloric data says this LAW is true
► combustion of glucose releases
heat = 686
kilocalories/mole
2nd LAW = Energy
transformations reduce the order of the universe
entropy is directional --- > toward
equilibrium (toward maximum disorder)
...
ENTROPY = amount of disorder in a system -
ENTROPY*
The Rules of Universe are simple :
Cities crumble,
stars go Supernova, & we're all
dying... (equilibrium...izing)
law
of ENTROPY
says... Degree of disorder of the Universe
-
(its randomness - its
entropy) CAN ONLY
INCREASE.
-
Cells obey Laws of
Chemistry & Physics
yet CELLS..... WOW ! .......become
more highly
ORDERED
as they divide & grow...
fertilized egg ---> wing of bird, a spider's
web, the human eye,
dividing cells, etc...
from fertilized egg cell... which Feeds, Grows & Differentiates = HOW?
for part of a system to become more ordered - lose entropy
- (such as
a cell),
its surroundings must become more disordered
- gain entropy -
FOODs (light & covalent bond energy) |
 |
cell reactions give increased order within cell |
 |
with release of
HEAT |
HEAT (most
disordered form of energy) =
max entropy
ENERGY IN ----> CELL STRUCTURE
----> ENERGY OUT
How do we measure energy changes in cells...
-
Josiah Gibbs (1880's) FREE ENERGY Equation
DG
= DH
- T
DS
free energy enthalpy
entropy
-
DG
is measure of amount energy change (D) in
a system that is able to do
Work...
-
DG
is a numerical
measure of how far a chemical reaction is from equilibrium...
- µ Disorder
Increases (Entropy Increases)... when useful energy,
that
which could be used to do work, is dissipated as heat...
-
- cells are
ISOTHERMAL - (-2o to 37o) - thus DH =
0 above
Enthalpy
may be thought of as
heat content
of a system
-
cells function within a very narrow temp range
[23o-37oC],
and
thus DH is negligible in the equation.
-
thus
DG can
PREDICT... the Direction of
Cellular Reactions...
TOWARD EQUILIBRIUM... toward Maximum ENTROPY
-
toward a release of free energy
-
-
-
-
-
-
-
CHEMICAL REACTON
A
<--->
B
Which Way is toward more Disorder?
DG = DG0’ +
RT
ln [p]/[r]
a derivation of Gibbs Free Energy equation
change in free energy content of a reaction...depends upon:
1. energy is stored in molecule's
covalent bonds
2. temperature is negligible...
i.e., cells are
isothermal, thus...
DG
= actual free energy at any time in a reaction
DGo' = standard free energy [free
energy change under standard
conditions]
R = gas constant ( 2 x
10-3 Kc/mol)
T = absolute temp (2730K
+ 0C)
ln = natural log
(conversion to log10 = 2.303)
3. at equilibrium
by definition
DG = 0
and we call [p]/[r]
= Keq
equilibrium constant
Free Energy Equation...
ΔG =
ΔG0'
+ RT ln [P]/[R]
@ equilibrium ΔG
= 0
0 =
ΔG0'
+ RT ln [P]/[R]
.... thus
rearranging
ΔG0'
= -RT ln [P]/[R]
@ equilibrium
[P] / [R]
= Keq
& @ 250C
... -RT
ln Keq = -(2.0)
(298) (2.303) lg10 Keq =
-[1372] lg10 Keq
thus..........
ΔG0'
= - [1372]
lg10 Keq
R = gas constant ( 2 x
10-3 Kc/mol)
T = absolute temp (2730K
+ 0C)
ln = natural log
(conversion to log10 = 2.303)
when we solved above equation for DGo' we could see
relationship* of Keq to
DGo’
The difference
between
ΔG
and
ΔG0'
ΔG0'
is a fixed value under
idealized conditions for a given reaction & indicates
in which direction
that reaction will proceed at standard conditions.
table
standard
conditions do not exist within a cell,
but ΔG0'
may be
useful to predict the direction of a reaction
at a specific given time.
ΔG is
determined by the concentrations present
at a given time and
is a measure of how far a reaction is from
equilibrium at that time.
Cell metabolism is essentially a
non-equilibrium condition.
Metabolism works by changing the relative
concentrations of reactants
and products to favor the progress of non-favored
catalytic reactions.
CHEMICAL
REACTIONS A <---->
B
Which Way &
Why?
EXERGONIC
REACTION - is one which releases free energy [
-
DG ]
Product (B) <<< energy
REACTANT (A) [energy stored in covalent bonds]
ex:
burning wood (cellulose)
glucose
polymer... potential energy.
breaks bonds, release heat & light ---> CO2 & H2O
fig 9.5*
cell respiration - cellular burning of glucose
molecules.
slower, multi-step process
that captures & releases
some energy... as
ATP
ENDERGONIC
REACTION - requires input of energy for
A --> B
Product (B) >>> energy than
REACTANT (A)
[ +
DG ]
ex:
photosynthesis (autotrophy)
glucose is made from CO2
+ H2O
--light-->
C6H12O6
energy
poor vs.
energy rich
CELL METABOLISM is
then a mix of...
Exergonic
& Endergonic reactions that occur inside of cells...
Concept Activities - chapter
8.3
-
Chemical Reactions & ATP.
How does Cell Metabolism really work
energetically?
for
RX's which share one or more intermediates (a
pathway)...
[ A-->B-->C-->D ]
the
overall free energy
change (DG) is the
sum of
indiv DG's
DGo'
Glu + Fruc
---> Sucrose
+ 5.5 Kc/m
ATP* ---> ADP + P
- 7.3 Kc/m
Glu +
ATP ---> G-1-P + Fruc ----> Suc + P
- 1.8Kc/m
COUPLED REACTIONS
- involves say... the linking of the hydrolysis of ATP
(a favored rx) to a thermodynamically
unfavored
reaction,
thereby
creating biological order (greater molecular structure).
another ex: synthesis of glutamine*
-
WHY
ATP ? ? ?
shouldn't any nucleotide work?
... the ENERGY MOLECULE of CELLS is
ATP
over the period of evolution, cells favored enzymes that
bound ATP & used its hydrolysis to drive endergonic reactions. |
 |
-
adenosine
triphosphate -
figure 6.8
* its
structure is its source of energy
1. electrostatic repulsion
2. resonance
3. sphere of
hydration
Concept Activities - chapter 8.3 -
The Structure of ATP*
copyright
c2010 Last update -
Friday, March 05, 2010
Charles Mallery,
Biology 150, Department of Biology, University of Miami,
Coral Gables, FL 33124
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key concepts*
