All living organisms share common chemical features despite their diversity. They are composed of the same basic macromolecules like DNA, RNA, and proteins which are constructed from a small set of common subunits like nucleotides and amino acids. While individual molecules behave physically and chemically, the highly organized complexity of living beings enables them to use energy to build and maintain intricate internal structures and replicate with high precision, distinguishing them from inanimate matter. Prebiotic evolution research suggests that simple organic molecules could arise spontaneously from non-living ingredients on the early Earth setting the stage for the emergence of life.

1. Presented by
Namadara Sandhya
ID.2022611005
Department of Microbiology

2.  Living organisms are composed of lifeless
molecules. When these molecules are isolated
and examined individually, they conform to
all the physical and chemical laws that
describe the behavior of inanimate matter.
 Biochemistry describes in molecular terms
the structure, mechanisms and chemical
processes shared by all organisms, and
provides organising principles that underlie
life in all of its diverse forms — Molecular
logic of life.

3. Some of the principles in the molecular logic of life;
• All macromolecules are constructed from a few simple compounds.
• Carbon atoms covalently joined with other carbon atoms and with the
hydrogen, oxygen and nitrogen.
• Organic compounds with relative molecular mass less than about 500, such as
amino acids, nucleotides and monosaccharides, serve as monomeric subunits
of macromolecules such as proteins, nucleic acids and polysaccharides.
• A single protein may have 1000 or more amino acids, and deoxyribonucleic
acids has millions of nucleotides
• eg. Escherichia coli have several proteins, nucleic acids molecules,
carbohydrates and lipids.
• DNA (Deoxyribonucleic acid) are constructed from only four different kinds of
simple monomeric subunits the deoxyribonucleotides
• RNA (Ribonucleic acid) are composed of just four types of ribonucleotides
• Proteins are composed of 20 different kinds of amino acids
• All proteins are built identical in all living organisms
• All living organisms build molecules from same kind of monomeric subunits
• The structure of a macromolecule determines its specific biological function
• Each genus and species is defined by its distinctive set of macromolecules

4. Diverse living organisms share common chemical features. Birds, beasts, plants, and soil
microorganisms share with humans the same basic structural units (cells) and the same kinds of
macromolecules (DNA, RNA, proteins) made up of the same kinds of monomeric subunits
(nucleotides, amino acids). They utilize the same pathways for synthesis of cellular components,
share the same genetic code, and derive from the same evolutionary ancestors. (“The Garden of
Eden” (detail), by Jan van Kessel, the Younger (1626–1679).)

5.  Evolution, as the term, signifies any
development or change adapting to the
environment. Chemical evolution connotes
changes of chemical substances, it thus
signifies that changes occur fundamentally in
the molecules.
 Prebiotic evalution: evolution before life
,describing ideas about how life began from a
‘prebiotic soup ‘
 PREBIOTIC SOUP:the seas and atmosphere as they existed on earth
before the existence of life, consisting primarily of an oxygen-free
gaseous mixture containing chiefly water, hydrogen, methane,
ammonia, and carbon dioxide.

6.  Frequently "chemical evolution" is used
synonymously for "abiotic" or "prebiotic
formation" of organic molecules in a cosmic
system, usually on the prebiotic (or primitive)
Earth.
 "Molecular evolution" has a broader meaning
than chemical evolution. The latter term also
covers self-assembly into higher structures (such
as membranes, protocells, cell-like systems,
proto cellular organelles) and the subsequent
evolution of protocells to the first living cells
("Urzellen" or progenotes).
 From this stage on, the evolution of living cells
and organisms to the multiplicity of
contemporary systems is called Darwinian
evolution. Several authors call the evolution of
protocells to the first living cells also proto-
Darwinian evolution.

7.  demonstrated it clearly that ultra violet radiation or
electrical discharges or heat or a combination of these can
produce complex organic compounds from a mixture of
methane (CH4), ammonia (NH3), hydrogen (H) and water
vapour. The ratio of methane , ammonia and hydrogen in
Miller's experiment was 2:1:2
 according to this theory ' life ' originated upon our earth
spontaneously from non living matter . First inorganic
compounds and then organic compounds were formed in
accordance with ever changing environmental conditions .
This is called chemical evolution which cannot occur under
present environmental conditions upon earth. Conditions
suitable for origin of life existed only upon primitive earth.
 The Miller-Urey experiment demonstrated that organic
molecules could form from abiogenic materials under the
constraints of Earth's prebiotic atmosphere. Later research
showed that amino acids can spontaneously form small
protein molecules (peptides).

8. •It is also shown that the RNA molecule can be artificially synthesized from nucleotides (nitrogen
containing compounds or bases) linked to sugar and phosphate groups.
In fact, in addition to carrying and translating genetic information, RNA acts like a catalyst, a
molecule that increases the rate of a reaction without itself being consumed.
• It is, thus, logical to accept that multiple forms of RNA existed in the prebiotic phase of
abiogenesis that led to the formation of life on Earth or in any wider context.

10.  What distinguishes living organisms from inanimate objects?
 First is their degree of chemical complexity and organization.
Thousands of different molecules make up a cell’s intricate internal
structures. By contrast, inanimate matter— clay, sand, rocks, seawater—
usually consists of mixtures of relatively simple chemical compounds.
 Second, living organisms extract, transform, and use energy from their
environment, usually in the form of chemical nutrients or sunlight. This
energy enables organisms to build and maintain their intricate
structures and to do mechanical, chemical, osmotic, and other types of
work. Inanimate matter does not use energy in a systematic, dynamic
way to maintain structure or to do work; rather, it tends to decay toward
a more disordered state, to come to equilibrium with its surroundings.
 The third attribute of living organisms is the capacity for precise self-
replication and self assembly, a property that is the quintessence of the
living state. A single bacterial cell placed in a sterile nutrient medium
can give rise to a billion identical “daughter” cells in 24 hours. Each of
the cells contains thousands of different molecules, some extremely
complex; yet each bacterium is a faithful copy of the original, its
construction directed entirely from information contained within the
genetic material of the original cell.

11. •Although the ability to self-replicate has no true analog in the nonliving world, there
is an instructive analogy in the growth of crystals in saturated solutions. Crystallization
produces more material identical in lattice structure to the original “seed” crystal.
Crystals are much less complex than the simplest living organisms, and their structure
is static, not dynamic as are living cells. Nevertheless, the ability of crystals to
“reproduce” themselves led the physicist Erwin Schrödinger to propose in his famous
essay “What Is Life?” that the genetic material of cells must have some of the
properties of a crystal.
•Each component of a living organism has a specific function. This is true not only of
macroscopic structures, such as leaves and stems or hearts and lungs, but also of
microscopic intracellular structures such as the nucleus or chloroplast and of individual
chemical compounds. The interplay among the chemical components of a living
organism is dynamic; changes in one component cause coordinating or compensating
changes in another, with the whole ensemble displaying a character beyond that of its
individual constituents. The collection of molecules carries out a program, the end
result of which is reproduction of the program and self-perpetuation of that collection
of molecules; in short, life.

12. Reference:
1. Klaus Dose.Prebiotic Evolution and the Origin of Life: Chemical and Biochemical
Aspects,Progress in Molecular and Subcellular Biology book , 1988, Volume 10 ISBN : 978-3-
642-73601-8.
2. Foundations of Biochemistry-part 1 book by Federal University of Minas Gerais
3. Dhavendra Kumar, Edward J. Steele, and N. Chandra Wickramasinghe (2020). Preface: The
origin of life and astrobiology , Advances in Genetics, Volume 106, 2020, Pages xv-xviii.
4. Schrödinger, E. (1944) What Is Life? Cambridge University Press, New York. [Reprinted (1956)
in What Is Life? and Other Scientific Essays, Double day Anchor Books, Garden City, NY.]