Termodynamic Trends in Biological Evolution
|
Biology Bulletin. Vol. 22, No. 1. 1995. pp. 1 - 9. Transated
from Izvestiya AN. Seriya Biologicheskaya. No. 1. 1995. pp. 5 -14. Original
Russian Text Copyright © by Gladyshev.
THEORETICAL BIOLOGY
Thermodynamic Trends in Biological Evolution
G. P. Gladyshev
Semenov Institute of Chemical Physics, Russian Academy
of Sciences, ul. Kosygina 4, Moscow, 117977 Russia. Received September
27,1993
Abstract - The available data on the thermodynamic stability
of supramolecular biological structures and variations in the chemical
composition of living organisms have allowed a macrothermodynamic model
of biological evolution to be developed experimentally. In this model,
the tendency toward a minimum of the specific Gibbs function of the formation
of supramolecular structures of living organisms causes variations in the
chemical composition and structure of living systems. It is shown that,
during the course of ontogenesis and phylogenesis, as well as long-lasting
stages in the evolution of the organic world, the biosystems (as a result
of the thermodynamic direction of evolutionary processes of the formation
of supramolecular structures) are enriched with energy-intensive chemical
substances, which displace water from these biosystems. The change in the
composition and structure of biostructures of an adaptive character is
also explained from the angle of macrothermodynamics.
1.THE HIERARCHY OF STRUCTURES AND MACROTHERMODYNAMICS
There are reasons to assume that biological evolution as a whole, phylogenesis,
and ontogenesis (like the general evolution of the Universe and the Earth's
geological evolution) have a thermodynamic tendency (Gladyshev, 1988; Gladyshev,
1993). This tendency is conditioned by the second principle of thermodynamics,
whose validity is not doubted.
It was noted earlier that understanding the specifics of the biological
evolution of matter in the light of the general laws of thermodynamics
is made simpler by consideration of the evolutionary process within the
framework of structural formation, which results in the emergence of structures
(j+1, j+2, ..., j+n) of a higher hierarchical
order from the structures (j) of a lower hierarchical order (Gladyshev,
1988; Gladyshev, 1993; Gladyshev, G. and Gladyshev, D., 1993).
It was shown that there is a correspondence between some of the series
of natural hierarchical structures (identified by the energies of their
formation) and the series of the average lifespan (relaxation) of these
structures. For instance, for an individual community of some closely related
species of organisms it may be written
(1)
where t is the average lifespan of the "free" metabolite
molecules, supramolecular structures, organelles, biological tissue cells,
organisms, populations, and communities.
There is a correspondence between series (1) and another, oppositely
directed, hypothetical series of the times of the establishing of imagined
quasi-equilibriums between different uniform structures inside one hierarchy
in a preset biomass volume.
Series (1) presents a geometric progression of the type ,
where tn is the average lifespan of structures of the
nth hierarchy in the identified biosystem; n = 1,2,3,...,
n; t0 is the standard time equal to the average
lifespan of the structure of the lower (standard) hierarchy (0) of the
series under review; and b is the constant for
a given series.
Law (1) makes it possible to lay the foundations of hierarchic thermodynamics
or macrothermodynamics (heterogeneous systems), which integrates methods
of classical thermodynamics, i.e., thermostatics and macrokinetics - relatively
slow, quasi-equilibrium processes. It is essential that series (1) makes
it possible to identify the thermostat (the environment) and the system
j under study, which forms, together with its thermostat (j+1),
a complete thermodynamic system [j+(j+1)]. This complete
thermodynamic system [j+(j+1)] is quasi-closed (at the times
of the existence of the system under study), since it is contained in a
thermostat of a higher hierarchical order (j+2). The latter points
to the existence in the biological world of quasi-closed systems (which
function against a background of practically constant kinetic factors determining
the flow of matter from the environment - the thermostat) and, to a certain
extent, helps avoid insuperable difficulties in applying the functions
of state to the description of the behavior of open systems of this type.
Indeed, in a general case, the functions of state of open systems, such
as, say, the Gibbs function (G) and the Helmholtz function (F),
cannot attain extreme values in these systems. In this situation, classical
thermodynamics, naturally, cannot predict the directions of processes.
Investigation of quasi-closed biosystems isolated with the aid of series
(1) and the use of a macrokinetic adsorption model (Gladyshev, 1988; Gladyshev,
1993) has allowed an important postulate to be formulated: the specific
values (per unit of volume) of the Gibbs function of intermolecular interactions
(where "-"
means the specific character of a value and "~" emphasizes the
heterogeneous character of the system) tend toward a minimum during the
formation of the supramolecular and supracellular structures of organisms:

where V is the volume of the system (m is the mass of
the microvolume) and x, y, z are the coordinates. This causes a
change in the local and general chemical composition of living organisms
and the accumulation of chemically energy-intensive matter by biosystems.
In accordance with the model, organisms must accumulate mainly those of
the most energy-intensive substances, which (in accordance with the aforesaid
postulate) have a relatively increased absolute value of the Gibbs function
of the formation of supramolecular structures (structural stabilization).
It follows from the model that it is possible to find a correlation between
the specific value of the Gibbs function of the formation of chemical compounds
of atoms or simple substances and
the specific value of the Gibbs function of the formation of supramolecular
structures of these chemical compounds - molecules - .
In accordance with the model, biostructures must form mainly from relatively
high melting substances in the case of enthalpy-controlled self-organization
or from relatively low melting structures in the case of entropy-controlled
self-organization.
With the aggregation of chemical substances in the water systems of
living organisms, these energy-intensive substances displace water relatively
slowly from organisms in the process of life.
Note that macrothermodynamics operates with the lifespans (relaxation)
of tl, biostructures. This means that it also relies
on the kinetic principle. However, according to the model, tl
depends primarily on the change in the thermodynamic function of state
-the Gibbs function - during the formation of the structure .
Thus, the adsorption model we use implies that ,
where R is the gas constant.
The macrothermodynamic approach was also used to propose the theory
of the behavior of biological systems on the basis of Le Chatelier-Braun's
principle. The latter's application to quasi-closed systems (interchanging
matter with its thermostat) is strictly valid only with definite restrictions
(de Heer, 1957, 1958). Nevertheless, it has proved possible to trace a
qualitative link between the intensity of some physical influences on the
organism and its reaction to them, as well as to substantiate the Weber-Fechner
empirical law.
2. THE APPROXIMATE CHARACTER OF THE MODEL
The studies carried out suggest a local and general thermodynamic tendency
in evolutionary processes. However, the real world of biostructures is
certainly more complex than the model, which is by definition inaccurate,
since it is based not only on thermostatics but also on macrokinetic principles.
Moreover, some of the mathematical problems of the model are insoluble
in principle, as are those of any other models of the thermodynamics of
complex systems, in which not only the work of expansion is performed (Denbigh,
1971; Sychev, 1981).
As noted above, according to our model, the isolated open system j has
(as does each of its locally isolated parts) its own thermostat (j+1),
whose parameters remain practically unchanged throught the lifespans of
the system (or part of it). The open system j under study, together
with its thermostat (j+1), forms a complete thermodynamic system
[j+(j+1)]. The model implies at the same time that practically
all transformations take place within the open system itself. The model
also implies that the formation of supramolecular structures of different
types is determined, as is that of the structures of higher hierarchical
orders, by thermodynamic factors alone. This is proved by the fact that
the energetics of supramolecular interactions is commensurate in scope
with kBT (kB - Boltzmann
constant, T - temperature), and local equilibriums are established
relatively quickly. The thermostat parameters are temperature (T):
pressure (p); chemical composition ;
tension of electric, magnetic fields, etc.). Of course, these parameters
often fluctuate noticeably in the space of minutes, hours, 24-hour periods,
and years, and organisms, as a rule, have to adapt to such fluctuations.
Moreover, each species (like each organism) has its own thermostat (habitat),
whose parameters undergo fluctuations in time-scales shorter than the life
of this species. The same is true of other biostructures, for instance,
cells functioning in biological tissues: their own thermostats of macromolecules
are contained in the relevant physiological fluids, etc.
Hence, it is obvious that the thermodynamic tendency in the processes
of suprastructural formation (with constant kinetic factors ensuring an
inflow of substructures into the system) can be clearly seen at times when
the essential (in Tolman's terminology) thermostat parameters are averaged.
This can take place with good approximation in cellular ontogenesis, the
ontogenesis of organisms, and even in phylogenesis of many species. As
for evolution over long periods of time, the real picture is even more
approximate. However, the available unambiguous experimental findings on
changes in the chemical composition of the biological tissue of different
animal and plant species suggest that in this case, too, it would be reasonable
to assume the existence of thermostats in the relevant time periods with
averaged parameters.
It should be re-emphasized for clarity that with this model it can be
assumed that all transformations occur in the isolated open biosystem itself,
while the formation of supramolecular structures of different types is
determined (as is that of the structures of higher hierarchical orders)
practically by thermodynamic factors alone.
On the other hand, sometimes the thermostat parameters change substantially
(a sharp climatic change, artificial modification of environmental conditions,
artificial selection, etc.). In such cases, there is evidence of revolutionary
changes in the environmental parameters and the transformation of the system
under study into a new one (with a new thermostat). In the process of revolutionary
change, the system becomes essentially unbalanced and open; it can be assumed
that the behavior of this system cannot always be studied by macrothermodynamic
methods. A system of this type can be studied in principle by kinetic methods
with the aid of the thermodynamic models of systems distant from the state
of equilibrium (Prigozhin, 1985).
The overall impression is that the fragmentation of biosystems into
their hierarchical components is a promising method of study, because it
helps establish the thermodynamic tendency (local and general) of evolutionary
changes. It appears that the motivating force of evolution is the "thermodynamic
force," which operates against a background of fluctuations of the
environmental parameters on either side of their averaged values. Note
that these fluctuations are accompanied by the adaptive reactions of biosystems
that also have a thermodynamic tendency. The said fluctuations are the
"source" of work: the environment performs work on the system.
Evidently, this work (on a par with work performed using solar and chemical
energy) is necessary to support life. The biosystem periodically expands
and contracts, as it were, absorbing and expelling matter, i.e., it is
a living "sponge" functioning against a background of relatively
small fluctuations of T, p, concentrations of chemical substances,
and other parameters of the relevant thermostat, with regard to some of
the averaged values of these parameters.
Let us examine some examples of variations in the chemical composition
and structure of individual molecules, macromolecules, and complex supramolecular
systems in ontogenesis and phylogenesis. The phenomena observed will be
interpreted from the angle of the macrothermodynamic model.
3. FACTUAL DATA
Some facts referring to variations in chemical composition and confirming
the validity of the macrothermodynamic model are discussed in a number
of works (Gladyshev, 1988; Kanungo, 1982).
It is perhaps appropriate here to look at the change in the chemical
composition and structures of biostructures and biosystems in vivo,
which correlate with the melting (denaturation) temperature of these structures,
as well as with the body temperatures of homoiothermal animals or the upper
temperature limit of the habitats of poikilothemial animals. The study
of such correlations is interesting, because a temperature change in phasic
transitions often permits judgement on variations in the thermodynamic
stability of structures.
3.1. Theoretical considerations. For closed systems, the dependence
of the change in the Gibbs function on T is determined by the Gibbs-Helmholtz
equation:
(2)
where D H is the change in enthalpy
during the process, and T and p are the temperature and pressure,
respectively. A similar equation was also written for open systems (p
and V are constant), whose composition was inconstant. Such an assumption
can be considered accurate only for i-substances having identical
values , ,
and , where
the index mi refers to the melting point of i-substances.
Nevertheless, it was found that the assumption made was reasonable for
a definite range of variations in the thermodynamic characteristics of
substances, since a correlation was revealed between the specific
Gibbs function of the unbalanced phasic transition of overcooled liquid
® solid body (with standard temperature of 298K)
and D T (Tm-298K) for
a wide range of organic compounds with Tm in the range
of 273-373K. The calculation was based on our approximate equation, an
analogue of the Gibbs-Helmholtz approximate equation:
(3)
where T0=298K, while the upper index im
indicates that the process of matter condensation is under study. The corresponding
results (Gladyshev, G. and Gladyshev, D., l 993) are presented in Fig.1.
It can be seen that the aforesaid postulate is correct, with a definite
degree of approximation. Indeed, substances with an increased show
a tendency to form more thermodynamically stable crystals, i.e., solid
structures (a more negative value ),
since the processes of crystallization of pure substances must be considered
to be mainly enthalpy-controlled. Note that the chemical energy capacity
of uniform natural compounds ( )
also grows with an increase in their .

Fig.1. The relationship of the Gibbs
specific function of unbalanced phasic transition of overcooled fluid ®
solid body (at 298.15K), (the
Gibbs specific function of structural formation), to
for a wide range of organic compounds with in
the 273-373K interval The calculation was made by equation (3), using reference
data (Weast, 1989 - 1990). The value is
calculated per unit mass. The correlation is preserved in recalculating
per unit of
volume.
In the case of entropy-controlled processes (for instance, the aggregation
of cells under the self-organization of cellular structures, the denaturation
of some proteins, etc.), the growth of the thermostability of structures
may be accompanied by a decrease in .
Note that our approach agrees with the approximate models of P.Flory,
who used the Gibbs-Helmholtz equation to establish the connection of Tm
synthetic copolymers with their composition and structure (Flory, 1953;
Mandelkern, 1964).
3.2. Variation in the composition of fatty acids participating
in the synthesis of fats. There is much data providing evidence that
the cells of microorganisms, plants, and animals adaptively change the
composition of fatty acids (fats) with a change in the temperature of the
environment. When the temperature of an organism Tl is
below the optimum level, there is an increase in the content of unsaturated
fatty acids (fatty acid residue) having a lower melting point Tm
(as compared with saturated and other unsaturated acids). This increase
is easily detected by the increase in the iodine number of the relevant
fatty acid fractions. When the temperature is above the optimum level,
the cells show an increase in the proportion of saturated acids having
a higher melting point.
The aforesaid is illustrated by Frenkel and Hoppe's classic data on
the relationship of the iodine number of phosphatides (lipids) or larvae
Calliphora erythrocephala and Phormia terranova to the maturation
temperature of flies (Aleksandrov, 1975, p.274). It can be seen in Fig.2
that at increased maturation temperatures the number of unsaturated acids
(characterized by a heightened iodine number and a lowered Tm)
drops. Other research results are given in a monograph (Aleksandrov, 1975)
and numerous reference publications (Libermann and Petrovsky, 1960; Marsh,
1990).

Fig.2. The relationship of the iodine
number (N) of phosphatides of (1) Calliphora erythrocepohala
and (2) Phormia terra-nova larvae to the temperature (T)
of maturation of flies.
Ignoring kinetic problems, i.e., the question of the mechanisms responsible
for compensatory change in the composition of fatty acids, and examining
this phenomenon from the angle of the macrothermodynamics of the formation
of lipid structures (against a background of constant kinetic factors),
we can draw the following conclusion.
The regularities observed can be easily interpreted on the basis of
our macrothennodynamic model, reasonably assuming that the correlation
of enthalpy-entropy control during the formation of "solid" uniform
structures containing fatty acids changes insignificantly in the adaptive
temperature interval.
Let us examine the data of Table 1 and show by examples that the observed
change in the chemical composition of fatty acids (fats) of biological
tissues in ontogenesis with a change in temperature is thermodynamically
advantageous.
Table 1 Several fatty acids whose residuals are contained
in natural fats*
Acid
|
Mol. mass
|
Tm, ° C
|
D Hm, cal/g
|
D T, K
|
,
cal/g
|
,
cal/mol
|
Saturated
|
|
|
|
|
|
|
n-Lauric (25 ° C)
|
200.3
|
43.2
|
43.7
|
18.2
|
-2.52
|
-503
|
Myristic (25 ° C)
|
228.4
|
54.0
|
47.5
|
29.0
|
-4.22
|
-964
|
Palmitic (25 ° C)
|
256.4
|
61.8
|
50.7
|
36.8
|
-5.57
|
-1428
|
Palmitic (5 ° C)
|
|
|
|
56.8
|
-8.60
|
-2204
|
Stearic (25 ° C)
|
284.5
|
68.8
|
52.6
|
43.8
|
-6.74
|
-1917
|
Unsaturated
|
|
|
|
|
|
|
Oleic (9c)
(25 ° C)
|
282.5
|
|
|
|
|
|
(a )
|
|
13.4
|
25.5
|
-11.6
|
+1.03**
|
+292**
|
(b )
|
|
16
|
|
-8.7
|
+0.767**
|
+217**
|
Oleic (9c) (5 ° C)
|
|
|
|
|
|
|
(a )
|
|
13.4
|
25.5
|
8.4
|
-0.747
|
-211
|
(b )
|
|
16
|
|
11.3
|
-0.996
|
-281
|
Elaidic (9t)
(25 ° C)
|
282.5
|
44.4
|
33.0
|
19.4
|
-2.02
|
-569
|
Elaidic (9t)
(5 ° C)
|
|
|
|
39.4
|
-4.09
|
-1157
|
Linoleic
(9c, 12c) (25 ° C)
|
280.5
|
-5.1
|
43.9
|
-30.1
|
+4.93**
|
+1383**
|
Linoleic
(9c, 12c) (5° C)
|
|
|
|
-0.1
|
+0.016**
|
+4.59**
|
*Values of Tm and are
taken from reference literature [16]. The estimations for are
done using Eq. (7) for the case of crystallisation (hardening) of substances
from over-cooled state at 25 and 5° C. **The
values of are
positive since the standard temperature 25°
C (5° C) is higher than Tm.
Under this condition, crystallisation of matter is impossible.
According to the model, the unit of volume Vi of adipose
tissue (cell) receives a flow of matter from the thermostat (environment),
in which a constant concentration of fatty acids (fats) is
maintained (the thermostat temperature within its physiological values
has no substantial influence on the values of ).
The volume Vi under review is like a chromatographic
column adsorbing incoming substances. Its calculation (Gladyshev, 1988;
Gladyshev, 1993) is based on the following obvious correlation:
(4)
where cs and cl are fatty acid concentrations
in the volume Vi in solid (adsorbed) and liquid state,
respectively; is
the change in the Gibbs function with the adsorption of fatty acids. Assuming
that are close
to values of
the crystallization of individual acids (Table 1), let us make these simple
operations:

For example, for palmitic acid at 25°C, .
This means that, in accordance with this model, from 1 mole (for convenience,
calculation is based on 1 mole, although the amount of matter in volume
V is much less) of this acid received from the thermostat by the
adipose tissue cell, 0.917 of a mole will pass into the solid phase and
0.083 of a mole will remain in the liquid phase. At 5°C, 0.982 of a mole
will go to the solid phase and 0.018 of a mole will stay in the liquid
phase. Thus, the amount of palmitic acid in the solid phase at a temperature
decrease from 25 to 5°C increases times.
For elaidic acid, at 25°C, 0.723 of a mole will pass into the solid
phase and 0.277 of a mole will remain in the liquid phase; at 5°C, 0.890
of a mole will pass into the solid phase and 0.110 of a mole will remain
in the liquid phase. Hence, 
For oleic acid, at 25°C, 0.408 of a mole will pass into the solid phase
and 0.592 of a mole will remain in the liquid phase; at 5°C, 0.624 of a
mole will pass into the solid phase and 0.375 of a mole will remain in
the liquid phase. Hence, 
Thus, according to the model calculation, on changing the temperature
of biological tissue from 25 to 5°C the amount of palmitic, elaidic, and
oleic acids will increase 1.07, 1.23, and 1.53 times, respectively. Although
our simple model ignores a number of effects, its results are in complete
agreement with the known facts indicating that with a decrease in animal
body temperature the relative amount of unsaturated acids (substances with
a relatively low Tm increases and that of saturated acids
decreases.
Such conclusions can be drawn from qualitative assessments directly
for the fats (lipids) themselves. In the future, it would be wise to make
computer-aided calculations of variations in the composition of different
natural fats, depending on the fatty tissue temperature of an animal.
Note that we have used for assessment an approximate equation (3) for
a relatively wide temperature range. However, this does not alter the general
tendency of the phenomena, because corrections for the change in thermal
capacity with a temperature in the cases we have studied, even though they
are essential, are commensurate in the cases under review (Ullmann's Encyclopedia
..., 1987; Stull et al., 1969).
Besides, we compared the value of only
for fatty acids rather than for fatty tissue itself. Nevertheless, this
circumstance does not change the general picture of the phenomenon either,
because the strict correlations between the thermodynamic characteristics
of fatty acids and fats (Tm and D
Hm) and their content of various fatty acid residues
(Ullmann's Encyclopedia ...,1987) are well-known.
Thus, the model calculations (made with relatively high precision for
added conviction) unambiguously confirm the applicability of the macrothermodynamic
model to the evolution of adipose tissue of organisms, explaining the causes
of variations in the chemical composition of fatty acids (fats) in terms
of the adaptation of organisms to the temperature conditions of their environment.
Relying on the macrothermodynamic model, it is possible to understand
the nature of change in the composition of adipose tissue in the ontogenesis
and phylogenesis of animals. However, in these cases conclusions should
be drawn taking into consideration the type of adipose tissue, sex, fatness,
and the conditions of keeping the animals (the character of feed, etc.).
With all the essential characteristics of the animal and the environmental
conditions remaining constant, the process of ontogenesis shows a regular
decrease in the water content of adipose tissue, which increases its chemical
energy capacity ( ).
The fatty acid composition of tissues in ontogenesis also changes (Table
2): evidently, the relative content of unsaturated acids often increases
(the iodine number grows), which also brings about an increase in the chemical
energy capacity of adipose tissue ( ).
Table 2. Comparative change in the quantity of the most
common fatty acids in fats in ontogenesis of cattle (kidney fat, October;
Dahl, 1957)
Acid
|
Calf fat
|
Cow fat
|
% acid
|
Saturated |
Myristic |
5.1
|
3.5
|
Palmitic |
31.8
|
31.2
|
Stearic |
24.1
|
22.7
|
Unsaturated |
Oleic (elaidic) |
32.0
|
37.0
|
Iodine number of sum of fatty acid |
37.7
|
40.9
|
In addition, a number of known examples indicate that the capacity of
the organism (biological tissue) to absorb lipids increases with the age
of animals. For instance, vitamin A and cholesterol absorption by the small
intestine of rats in ontogenesis increases substantially (Table 3; Cristofalo,1985).
Table 3. Absorption of vitamin A and cholesterol by small
intestine of rats in standard conditions after Hollender and Morgan (Cristofalo,
1985)
Age of rat
|
Percentage of absorbed matter per h
|
vitamin A
|
cholesterol
|
1
|
-
|
14
|
1.5
|
25
|
-
|
2
|
-
|
17
|
12
|
28
|
18
|
19
|
29
|
-
|
20
|
-
|
25
|
25
|
33
|
-
|
37
|
-
|
37
|
39
|
37
|
-
|
42
|
-
|
38
|
Thus, despite some limitations of the simple model used and the influence
of many factors (including genetic ones) on the thermodynamic parameters
of lipid-containing living systems, one can draw this conclusion: adaptive
and evolutionary changes in the lipid composition of living systems evidently
always have a thermodynamic tendency.
3.3. Variations in the structure and composition of collagen.
It is an accepted view (Nikitin et al., 1977) that change in the
properties of collagen structures in ontogenesis has an adaptive character.
It has been found that the temperature of collagen denaturation in homoiothermal
animals is close to their body temperature and in poikilothermal animals
is close to the upper temperature limit of their environment (i.e., the
highest body temperature of an animal).
Figure 3 shows the generally known dependence of the temperature of
denaturation Td of collagen molecules on body
temperature (homoiothermal animals) or on the upper temperature limit of
the environment (poikilothennal animals), Tl, (Rigby,
1971; Nikitin et al., 1977). In view of the macrothermodynamic model,
it can be assumed that adaptation of the composition and structure of collagen
tissue in vivo, just as in the case of fats, has a thermodynamic
character. Naturally, Td > Tl
and hence ,
has a negative value in the formation of collagen structures. The values
D Td= Td-Tl
for the collagen structures of all the animal species studied vary insignificantly.
This means that the relative thermodynamic stability of the collagen structures
of animals referred to T, of each type is practically identical.
This confirms the reasons for using the concept of Aleksandrov et
al. (1975) concerning the semistable state of biological macromolecules.
However, the "absolute" thermodynamic stability of collagens
referred to, standard T0 [(see equation (3)], is evidently
determined primarily by their Tm(Td)
and in the icefish, cod, tuna, snail (cow, rat, human), and swine series
tends to grow. At the same time, ignoring the variation in the structure
and chemical composition of collagen, it is difficult to draw from Fig.
3 an unambiguous conclusion on the thermodynamic tendency of evolution.
Also unclear are the role and fluctuations of the thermostat parameters
of the environment and the changes

Fig. 3. The relationship of the denaturation
temperature (Td) of collagen molecules to the body temperature
(homoiothermal animals) or to the upper temperature limit of the environment
(poikilothermal animals): (1) swine, parasitic nemathelminthic worms -
Ascaris and Acanthocephala; (2) human, rat, cow; (3) snail; (4)
tuna; (5) cod; (6) icefish.
in the degree of entropy control which come about as a result of temperature
changes with the formation of protein structures (Brandt and Hunt, 1967;
Tiktopulo et al., 1979; Cantor and Schimmel, 1980; Hochachka and
Sommero, 1973).
On the whole, however, the known facts create the impression that the
evolution of collagen structures, although it is determined primarily by
genetic factors, has a thermodynamic tendency. For instance, there is a
certain parallelism in the temperature increase of the hydrothermal contraction
of collagen-containing tissues in both the transition from lower to higher
verterbrates and the ontogenesis of mammals. It is believed (Nikitin et
al., 1977) that this phenomenon is primarily an ontogenetic recapitulation
of the process of increasing the thermal stability of supramolecular collagen
structures, which occurred in the phylogenesis of vertebrates.
It is assumed that among the factors determining the thermal stability
of collagen-containing tissues only one coincides in phylogenesis and ontogenesis
- the increasing degree of intermolelcular interactions. This is a key
factor in ontogenesis, while in phylogenesis (when the genetic factor is
in operation) its role is not significant. Nevertheless, it appears that
the general change in ,
counted off from the standard level is determined by the sum total of changes
in the Gibbs function associated with the adaptation of the organism and
evolutionary changes proper (in ontogenesis and phylogenesis).
The thermodynamic tendency in ontogenesis can be linked, for instance,
to the loss in the water content of the native Achilles tendons of animals
(Table 4; Nikitin et al., 1977, p. 128) as they grow old.
Table 4. Water content in tendons of rats of different
age (after Nikitin et al., 1977)
Age, weeks
|
Water content, %
|
2
|
78.3
|
4
|
70.2
|
12
|
63.9
|
48
|
58.9
|
96
|
58.3
|
It is clear that one of the factors responsible for the increase in
the thermal stability of the supramolecular structures of collagen in phylogenesis
is the change in its chemical composition, which is associated primarily
with an increase in the relative amount of imino acid residues in protein
macromolecules.
There are also many other data on the evolution of collagen, which can
be interpreted in the light of the thermodynamic tendency of evolution.
However, it should be re-emphasized that the evolutionary change in the
composition and structure of proteins is associated with a complex of thermodynamic
and purely genetic factors. The role of the latter is determined by the
DNA structure.
3.4. The change in the composition and structure of nucleic
acids. Just as in the case of lipids and proteins, many facts (Aleksandrov,
1975, 1985; Saenger, 1984; Cantor and Schimmel, 1980) point to the thermodynamic
nature of the correspondence between the melting temperature of nucleic
acids, their supramolecular structures, and the temperature conditions
of the life of the species (i.e., the temperatures of the relevant thermostats).
This does not contradict Aleksandrov's kinetic principle of semistability
and allows quantitative assessment (through values)
of the "conformational strength" of biological supramolecular
structures.
On the other hand, there are known examples of a thermodynamic tendency
in the variation of the composition and structure of nucleic acids (chromatin)
in ontogenesis. It has been found that the thermodynamic stability of nucleic
acids is determined by the content of G-C pairs, as well as by the
ability of these biopolymers to form complexes with proteins and various
low-molecular substances, and other known factors (Cantor and Schimmel,
1980; Gladyshev, 1988). Hence it is clear that efforts to accurately identify
the general correlation between the degree of an animal (plant) evolution
and the composition of nucleic acids have failed. For instance, the classic
data (Marmur and Doty, 1962) on the relationship of the denaturation temperature
(Tm) of different DNA to their content of G-C
pairs gives no reason to conclude that this relationship is linked with
the evolution of the organic world. It appears that only some cases contain
dependable evidence of a relationship between the trend of evolution and
the content of G-C pairs, whose growth (on a par with other factors)
contributes to the increased thermodynamic stability of submolecular structures
formed with the participation of DNA and RNA (Gladyshev, 1988).
The increase in the melting temperature of chromatin in ontogenesis,
as is assumed, unambiguously indicates its evolutionary aging in ontogenesis
(Gladyshev, 1988). This conclusion correlates with a certain reduction
in the metabolic activity of DNA at the final stages of ontogenesis, which
is associated with the increased stabilization of this nucleic acid. Let
us assume that the average value of in
the formation of the chromatin structure (referred to the pair of complementary
bases - nucleotides) is equal to -0.025 kcal/(Kґ
unit). Using the equation (3), it is easy to estimate the gain in changing
the Gibbs function by increasing Tm of the chromatin
by 1K in ontogenesis (when the DNA composition is unchanged): 
Now lei us examine one of the models of biological evolution primarily
associated with DNA evolution.
Under the action of solar energy, substances that are thermodynamically
stable in the primeval conditions of the Earth transform (as they do today)
into various photosynthesis products (Calvin, 1969; Ponnamperuma, 1972).
Then, as a result of "dark reactions," these products transform
into various substances, and are selected by kinetics, in accordance with
the laws of chemical thermodynamics. After this, the local thermodynamics
of supramolecular processes selects the most stable suprastructures from
the full range of chemical substances, a process that is facilitated by
the tendency of im
biostructures toward a minimum, and these suprastructures accumulate in
the micro- and macrovolumes of systems. Individual macromolecules and suprastructures
are reduplicated by possible matrix mechanisms. The selected compounds
are primarily nucleic acids, whose composition and structure slowly adapt
(under the action of thermodynamic factors) to environmental nature, and
include proteins, whose composition is determined by DNA itself. This explains
the feedback between protein structure and DNA. In our model, this link
is of a thermodynamic nature.
The existence of correlations between Tm of chemical
substances and the thermodynamic stability of suprastructures (crystals)
forming during crystallization from an overcooled state confirms the presented
model.
The degradation processes of the disintegration of chemical compounds
parallel the synthesis processes. However, living systems resist this and
tend to preserve their state. This tendency is of a thermodynamic nature.
The biosystems reproduce perishing supramolecular structures. In the meantime,
as noted above, thermodynamics contributes to selecting the most stable
structures.
It is thermodynamically advantageous for macromolecular chains to pair
with similar chains and surround themselves (through supramolecular contacts)
with the renewed "young" matter of living organisms. Therefore,
evolution selects those thermodynamically preferable processes that contribute
to cell division and DNA preservation. All this occurs against a background
of fluctuations in the thermostat (environment) parameters, which, on a
par with other factors, support life. Thermodynamic factors contribute
to the stabilization of all complex biological structures, thus creating
higher hierarchical orders of the biological world.
Thus, it can be assumed that adaptive and evolutionary changes in the
composition and structure of supramolecular structures containing nucleic
acids have a thermodynamic tendency. However, for the time being it is
rather difficult to ascertain this tendency in view of the influence of
many factors.
4. CONCLUSION
The model we have proposed makes it possible to identify, relying on
the principles of macrothermodynamics and static approaches, the tendency
of the evolutionary processes of structural formation leading to the emergence
and existence of hierarchical biostructures. Similarly to classical thermodynamics
(thermostatics), macrothermodynamics "sets" the axis of time
and can only study change occurring in time in the specific functions of
state during the structural formation in biosystems of preset hierarchical
orders.
Macrothennodynamics is not concerned with the mechanisms of phenomena.
However, despite these limitations, the macrothermodynamic method can prove
quite effective in the study of ontogenesis, phylogenesis, and biological
evolution in general on a solid physical foundation.
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Academy Order of Glory

Institute of Physico-Chemical Problems of Evolution

Commmerce and Law Institute
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