Title: Biological Energy
1Biological Energy
6 types of work requiring energy to
accomplish 1) biosynthesis formation of new
bonds and generation of molecules
macromolecule formation, replication and growth,
etc. 2) mechanical work physical change in
orientation or location flagellar motion,
vesicle transport, muscle contraction, etc 3)
concentration work transporting molecules
against a gradient ie. sugars into a
cell 4) electrical work movement of ions across
a membrane 2/3 of energy at rest required
work in mitochondria and chloroplasts 5) heat
increase in temperature takes energy to stay at
optimum temp. 6) bioluminescence production of
light (specialized type of work)
2Biological Energy
phototroph organism capable of capturing energy
from light chemotroph organism requiring
intake of chemicals to generate energy in the
absence of light, phototrophs can function as
chemotrophs phototrophs required-- chemotrophs
depend on them for survival cellular
respiration transfer of electrons from chemical
bonds to an electron receptor if the electron
receptor is oxygen, process is called aerobic
respiration energy is constantly flowing through
the biosphere energy flow is accompanied by a
flow of matter (food, etc)
3Thermodynamics
thermodynamics study of energy flow-- hard core
chemistry bioenergetics thermodynamics applied
to living creatures system unit being
considered when looking at energy flow closed
system isolated from the environment open
system energy can enter and exit from the
environment surroundings universe outside of
the system energetic state all of its variable
properties are held constant systems could be
held in many different states, some excited, some
not total energy change is determined by the
initial and final states, not the pathway
the system took to change from its initial to
final states calorie energy required to raise 1
gram of water 1 degree centigrade joule another
unit of energy equal to 4.184 calories
4Thermodynamics
First Law of Thermodynamics Law of Conservation
of Energy the total amount of energy in the
universe remains constant, although the
form of the energy may change ie. energy
cannot be created or destroyed, only
changed Internal energy energy stored in the
system impractical for general use DE change
in internal energy DE Efinal-Einitial enthalpy
heat content of a system H E PV for
biological systems PV0, so DH DE exothermic
reaction decreases in enthalpy -DH endothermic
reaction increases in enthalpy DH
5Thermodynamics
Second Law of Thermodynamics universe tends
toward greater disorder energy must come from
somewhere to increase order in a system Entropy
(S) measure of disorder in a system DS change
in entropy another way of saying the second
law DSgt0 Free Energy (G) measure of
spontaneity of a reaction DG change in free
energy for biological systems, DG DH - TDS
DG considers enthalpy (heat/energy) and entropy
(order) of system for a reaction to occur
spontaneously, DGlt0 if DGgt0, energy must be
added to the system to make a reaction go if
DGlt0, a reaction CAN go, but doesnt necessarily
mean it WILL go ie. paper can burn it doesnt
spontaneously ignite
6Thermodynamics
chemical equilibrium a reaction that proceeds
equally either direction A B note does not say
anything about amount of A or B equilibrium
constant Keq ratio of products and reactants at
equilibrium Keq Beq/Aeq with
concentrations in molar (M) for a more general
reaction, aA bB cC dD Keq
CcDd AaBb
7Thermodynamics
example light converts 11-cis retinal to
all-trans retinal if Keq 1x10-2 and the
concentration of retinal 1 mM, how much of the
retinal is in each form?
11-cis all-trans Keq all-trans/
11-cis 11-cis all-trans 1mM 1x10-2
x/(0.001-x) let x all-trans retinal 1x10-5-
1x10-2x x 1x10-5 1.01x x 9.9x10-6 M
all-trans retinal .01 mM 10 mM 11-cis
retinal 1-all-trans 0.99mM all
calculations should be done using Molars!
8Thermodynamics
obviously, the further a reaction is away from
equilibrium, the larger the difference in free
energy DG -RTln Keq RTln
T temperature (in degrees Kelvin) R gas
constant 1.987 cal/molK
B A
if B and A are at equilibrium, then DG 0
and there is no net change
9Thermodynamics
What is DG for the system 11-cis
all-trans if T298 oK Keq 1x10-2, and
11-cis .1 and all-trans .9
DG -RTln Keq RTlnall-trans/11-cis DG
-1.987298ln 1x10-2 1.987298ln(.9/.1) DG
2727 1301 DG 4028 cal/mol
what if ratios are reversed 11-cis .9 and
all-trans.1
DG -1.987298ln 1x10-2 1.987298ln(.1/.9) D
G 2727 - 1301 DG 1426 cal/mol
10Thermodynamics
What is DG for the system 11-cis
all-trans if T298 oK Keq 1x10-2, and
11-cis .9999 and all-trans .0001
DG -1.987298ln 1x10-2 1.987298ln(.0001/.99
99) DG 2727 - 5454 DG -2727 cal/mol
for an equilibrium value, DG represents which
direction the reaction will move negative
in forward direction, positive in reverse
direction
11Thermodynamics
DG is generally given in terms of a standard
state (arbitrary, convenient values that are
usually true ie. T298 oK 25 oC, for us,
pH7.0, concentrations of 1.0 M for all
reactants) putting standard conditions into the
normal DG equation gives DGo -RTln Keq
-RTln(1/1) DGo -RTln Keq
12Living Thermodynamics
DG for equilibrium gives the direction that a
particular reaction will go if a cell would
reach a steady state where reactions are no
longer occurring, it would be dead Cells
are in a dynamic equilibrium, with reactactants
maintained at a constant concentration by
taking in both energy and more matter Cells
require a constant energy and matter stream to
stay organized and alive-- ability to keep
carrying out reactions far from equilibrium
13ATP
ATP is a high energy compound-- it has chemcial
bonds that contain a large amount of chemical
energy phosphates are connected to each other as
phosphoanhydride bonds these are where the
majority of the energy is stored. hydrolyze 1
phospate (ATP to ADP) for most reactions for
those that demand more energy input, ATP can
convert to AMP (ie. during the charging of
tRNAs for protein synthesis)
why is ATP considered a high energy molecule?
14ATP
two features make ATP high energy 1) Charge
repulsion each phosphate group is negatively
charged energy will be released when they move
apart actually the lesser of the two features
which make ATP high energy 2) Resonance
stabilization has to do with the chemical
structure of phospate ions (and also applies
to carboxyl groups as well) phosphate is drawn
with 1 double bond and 1 negative charge in
reality, the unshared electron is partially
shared between all of the oxygen atoms around
phosphorus, giving each partial negative charge
15ATP
when the phosphates are bound to other things,
they are higher in energy when a phosphate is
bound to another phosphate, it is even higher
energy ie. middle oxygen can't be shared, but
is bound by two phosphorus atoms anhydride bond
is rather higher in energy in energy metabolism,
though, phosphate must be transferred to ATP
from something higher in energy-- by that
logic ATP is only middle in energy phosphates
must travel down from the highest energy states
to the lowest transfer of phosphates is
essential energy metabolism for all forms of life
16Thermodynamics Problem
Consider this equilibrium reaction from
glycolysis where glyceraldehyde 3-phosphate
(G3P) converts to dihydroxyacetone phosphate
(DHAP) in the presence of the enzyme
(catalyst) triosephosphate isomerase. If the Keq
of this catalyzed reaction is 22.2, what is the
equilibrium concentration of G3P if DHAP
10mM?
O
O
O
OH
HO-P-O-CH2-CH-CHO
HO-P-O-CH2-C-CH2-OH
O-
O-
DHAP 10mM .01 M G3Px Keq 22.2 Keq
DHAP / G3P 22.2 0.01 / x x 0.01 / 22.2
4.5x10-4 0.45mM
17Thermodynamics Problem
given the dipeptide glycylalanine hydrolyzing in
the presence of water to form glycine and alanine
according to the reaction below. If the Keq of
the reaction is 20 and the glycylalanine 1 mM,
what are the concentrations of glycine and
alanine at equilibrium?
O
O
O
O
NH3-CH-C-O-
NH3-CH2-C-O-
NH3-CH2-C-NH-CH-C-O- H2O
CH3
CH3
Water is ignored because under standard
conditions it is in great excess
xGA and GA .001 M
Keq GA / GA 20 xx/.001 0.02 x2 x
sqrt(0.020)0.14 M 140 mM because Keq
squares the products,
it is vital to
use Molar concentrations
18Thermodynamics Problem
given the dipeptide glycylalanine hydrolyzing in
the presence of water to form glycine and alanine
according to the reaction below. If the Keq of
the reaction is 20 and 1 M of glycine is added,
what is the A if glycylalanine at equilibrium
is 1 M?
O
O
O
O
NH3-CH-C-O-
NH3-CH2-C-O-
NH3-CH2-C-NH-CH-C-O- H2O
CH3
CH3
G1x Ax GA1 Keq GA/GA 20 (1
x) x / 1 20 1 x x2 0 x2 1x - 20
quadratic equation which can be a pain to solve
0(x5) (x-4) therefore x4 or x-5. since you
cant have a negative A, A 4 M