BIOCHEMISTRY
(1st Sem Lecture Notes)
I. SCOPE OF STUDY OF BIOCHEMISTRY
Biochemistry is the branch of science that explores the chemical substances present in living organisms and
how these substances interact with one another. It also involves applying chemical principles and techniques to
understand biological and physiological processes.
Principal Areas of Biochemistry
Biochemistry aims to explain the structure, organization, and function of living matter at the molecular level. Its
study is generally categorized into three main areas:
1. Structural Chemistry
– Focuses on how the molecular structure of biochemical substances relates to their roles in biological
systems.
2. Metabolism
– Examines the full range of chemical reactions and processes that take place within living organisms.
3. Molecular Genetics
– Explores the chemical nature of the substances and processes involved in storing and transmitting
genetic information.
– Seeks to understand heredity and gene expression from a molecular perspective.
Importance of Biochemistry
As an interdisciplinary science, biochemistry draws strength from other disciplines, and nourishes them
in return. The figure below shows the interrelation of Biochemistry to other disciplines.
, II. DISTINCTIVE PROPERTIES OF LIVING SYSTEMS
Molecules by themselves are not alive, but when assembled in the right complexity and quantity, they
form living organisms. What sets these living systems apart from non-living matter are several
remarkable characteristics, including the following:
1. Living systems are complicated and highly organized.
Although made from lifeless molecules, living systems consist of cells—often of various
types—that contain specialized subcellular structures called organelles. These organelles are built from
large, complex polymeric molecules known as macromolecules. Remarkably, macromolecules display
an intricate and highly ordered three-dimensional structure, even though they are assembled from
relatively simple chemical units such as sugars and amino acids.
2. Biological structures of living systems serve functional purposes.
Biological structures serve essential functions in an organism's survival. From the visible parts
of organisms, like limbs and organs, to the chemical agents of metabolism, including enzymes and
metabolic intermediates, each component has a specific biological role. This functional aspect of
biological structures is what distinguishes biology from the physical sciences such as chemistry,
physics, and geology. In biology, it is always relevant to explore the purpose behind structures,
patterns, or arrangements—specifically, the functional role they play within the organism.
3. Living systems are actively engaged in energy transformations.
The sun is the primary source of this energy. Solar energy is captured by photosynthetic
organisms—those capable of converting light energy through photosynthesis—and then transferred
through the food chain, first to herbivores and eventually to carnivorous predators at the top of the food
pyramid (see figure below). The biosphere thus acts as a system that facilitates the continuous flow of
energy. Organisms capture a portion of this energy—either directly via photosynthesis or indirectly
through food metabolism—by producing specialized energized biomolecules, most notably ATP and
NADPH. These biomolecules store chemically usable energy, and when they participate in reactions
within the cell, they release energy that drives various unfavorable processes. In this way, ATP,
NADPH, and related compounds function as energy sources for vital cellular activities such as
biosynthesis, movement, osmotic work (moving substances against concentration gradients), and in
some organisms, light production (bioluminescence).
-An organism only reaches equilibrium with its nonliving surroundings upon death. While alive, it
remains in a state defined by a continuous flow of energy, which enables it to sustain its internal order
and biological functions—far from thermodynamic equilibrium. This condition, known as the steady
state, appears stable but is actually dynamic: energy and materials are constantly being consumed and
used to maintain this organized state. In contrast, the non-living world naturally progresses toward
disorder—a state described in thermodynamics as maximum entropy. Living organisms resist this trend
by continuously investing energy to preserve their intricate structures and activities.
4. Living systems possess an extraordinary ability to self-replicate.
Across generations, organisms are able to produce nearly identical copies of themselves. This
self-replication occurs through various mechanisms—from the simple binary fission of bacteria to the
complex process of sexual reproduction in plants and animals. Regardless of the method, it is marked
by a remarkable level of accuracy. Interestingly, if this accuracy were even higher, it could actually
hinder evolution, which relies on natural selection acting on slight variations in individual organisms’
ability to survive and reproduce. These small variations are crucial for adaptation and evolutionary
progress.
(1st Sem Lecture Notes)
I. SCOPE OF STUDY OF BIOCHEMISTRY
Biochemistry is the branch of science that explores the chemical substances present in living organisms and
how these substances interact with one another. It also involves applying chemical principles and techniques to
understand biological and physiological processes.
Principal Areas of Biochemistry
Biochemistry aims to explain the structure, organization, and function of living matter at the molecular level. Its
study is generally categorized into three main areas:
1. Structural Chemistry
– Focuses on how the molecular structure of biochemical substances relates to their roles in biological
systems.
2. Metabolism
– Examines the full range of chemical reactions and processes that take place within living organisms.
3. Molecular Genetics
– Explores the chemical nature of the substances and processes involved in storing and transmitting
genetic information.
– Seeks to understand heredity and gene expression from a molecular perspective.
Importance of Biochemistry
As an interdisciplinary science, biochemistry draws strength from other disciplines, and nourishes them
in return. The figure below shows the interrelation of Biochemistry to other disciplines.
, II. DISTINCTIVE PROPERTIES OF LIVING SYSTEMS
Molecules by themselves are not alive, but when assembled in the right complexity and quantity, they
form living organisms. What sets these living systems apart from non-living matter are several
remarkable characteristics, including the following:
1. Living systems are complicated and highly organized.
Although made from lifeless molecules, living systems consist of cells—often of various
types—that contain specialized subcellular structures called organelles. These organelles are built from
large, complex polymeric molecules known as macromolecules. Remarkably, macromolecules display
an intricate and highly ordered three-dimensional structure, even though they are assembled from
relatively simple chemical units such as sugars and amino acids.
2. Biological structures of living systems serve functional purposes.
Biological structures serve essential functions in an organism's survival. From the visible parts
of organisms, like limbs and organs, to the chemical agents of metabolism, including enzymes and
metabolic intermediates, each component has a specific biological role. This functional aspect of
biological structures is what distinguishes biology from the physical sciences such as chemistry,
physics, and geology. In biology, it is always relevant to explore the purpose behind structures,
patterns, or arrangements—specifically, the functional role they play within the organism.
3. Living systems are actively engaged in energy transformations.
The sun is the primary source of this energy. Solar energy is captured by photosynthetic
organisms—those capable of converting light energy through photosynthesis—and then transferred
through the food chain, first to herbivores and eventually to carnivorous predators at the top of the food
pyramid (see figure below). The biosphere thus acts as a system that facilitates the continuous flow of
energy. Organisms capture a portion of this energy—either directly via photosynthesis or indirectly
through food metabolism—by producing specialized energized biomolecules, most notably ATP and
NADPH. These biomolecules store chemically usable energy, and when they participate in reactions
within the cell, they release energy that drives various unfavorable processes. In this way, ATP,
NADPH, and related compounds function as energy sources for vital cellular activities such as
biosynthesis, movement, osmotic work (moving substances against concentration gradients), and in
some organisms, light production (bioluminescence).
-An organism only reaches equilibrium with its nonliving surroundings upon death. While alive, it
remains in a state defined by a continuous flow of energy, which enables it to sustain its internal order
and biological functions—far from thermodynamic equilibrium. This condition, known as the steady
state, appears stable but is actually dynamic: energy and materials are constantly being consumed and
used to maintain this organized state. In contrast, the non-living world naturally progresses toward
disorder—a state described in thermodynamics as maximum entropy. Living organisms resist this trend
by continuously investing energy to preserve their intricate structures and activities.
4. Living systems possess an extraordinary ability to self-replicate.
Across generations, organisms are able to produce nearly identical copies of themselves. This
self-replication occurs through various mechanisms—from the simple binary fission of bacteria to the
complex process of sexual reproduction in plants and animals. Regardless of the method, it is marked
by a remarkable level of accuracy. Interestingly, if this accuracy were even higher, it could actually
hinder evolution, which relies on natural selection acting on slight variations in individual organisms’
ability to survive and reproduce. These small variations are crucial for adaptation and evolutionary
progress.
