An Overview of Cell Structure and Function
The study of cell structure and function focuses on understanding how cells operate at the
molecular level using the basic tools of genetics, chemistry, and physics. Scientists are
especially interested in processes such as DNA replication, protein synthesis, and the
regulation of gene activity. Research usually begins with whole cells and later moves to
detailed biochemical and biophysical studies of individual cellular components.
Much of molecular biology research has been based on three main model organisms:
Escherichia coli, Saccharomyces cerevisiae (yeast), and Drosophila melanogaster (fruit fly).
These organisms are chosen because they grow easily, are inexpensive to maintain, and
display many fundamental biological processes. E. coli has been studied the most because of
its rapid growth and simple structure. Although eukaryotic organisms are needed to study
certain complex processes, studies have shown that basic cell principles are similar in all
living cells.
Cells require extremely large amounts of information in order to grow, function, and
reproduce. A useful way to understand this is by comparing a cell to a self-sufficient factory.
Just like a factory needs many machines and tools, a cell contains thousands of specialized
molecules, mainly enzymes, that carry out specific chemical reactions. These reactions occur
in water at near-neutral pH, conditions that are difficult for ordinary chemical processes but
are well controlled inside cells.
The instructions for building and controlling all cellular machines are stored in DNA, which
acts as the cell’s information library. This genetic information has been shaped by evolution
to ensure proper growth and division. DNA is protected by its double-stranded structure,
which allows damaged parts to be repaired using the complementary strand. More complex
cells also protect their genetic information by having extra copies of DNA.
Prokaryotic cells, such as E. coli, have a relatively simple structure. Their cell envelope
consists of three main layers: an outer membrane, a peptidoglycan cell wall, and an inner
(cytoplasmic) membrane. The outer membrane contains lipopolysaccharides and special
proteins that form pores, allowing small molecules to enter while keeping harmful substances
out. The peptidoglycan layer provides strength and maintains the cell’s shape. The inner
membrane contains many proteins involved in transport and energy production. The space
between the two membranes is called the periplasmic space.
Inside the inner membrane is the cytoplasm, which is a highly concentrated solution of
proteins and other molecules. It contains more than 2,000 different types of proteins that
perform various functions. The amounts of these proteins change depending on
environmental and growth conditions. Although proteins can easily stick together, most
remain properly folded and separated. However, when foreign proteins are produced in large
amounts, they may form inactive clumps known as inclusion bodies.
The cytoplasm also contains the cell’s DNA and many ribosomes. Ribosomes are made of
RNA and protein and are responsible for protein synthesis. In bacteria, DNA is not enclosed
The study of cell structure and function focuses on understanding how cells operate at the
molecular level using the basic tools of genetics, chemistry, and physics. Scientists are
especially interested in processes such as DNA replication, protein synthesis, and the
regulation of gene activity. Research usually begins with whole cells and later moves to
detailed biochemical and biophysical studies of individual cellular components.
Much of molecular biology research has been based on three main model organisms:
Escherichia coli, Saccharomyces cerevisiae (yeast), and Drosophila melanogaster (fruit fly).
These organisms are chosen because they grow easily, are inexpensive to maintain, and
display many fundamental biological processes. E. coli has been studied the most because of
its rapid growth and simple structure. Although eukaryotic organisms are needed to study
certain complex processes, studies have shown that basic cell principles are similar in all
living cells.
Cells require extremely large amounts of information in order to grow, function, and
reproduce. A useful way to understand this is by comparing a cell to a self-sufficient factory.
Just like a factory needs many machines and tools, a cell contains thousands of specialized
molecules, mainly enzymes, that carry out specific chemical reactions. These reactions occur
in water at near-neutral pH, conditions that are difficult for ordinary chemical processes but
are well controlled inside cells.
The instructions for building and controlling all cellular machines are stored in DNA, which
acts as the cell’s information library. This genetic information has been shaped by evolution
to ensure proper growth and division. DNA is protected by its double-stranded structure,
which allows damaged parts to be repaired using the complementary strand. More complex
cells also protect their genetic information by having extra copies of DNA.
Prokaryotic cells, such as E. coli, have a relatively simple structure. Their cell envelope
consists of three main layers: an outer membrane, a peptidoglycan cell wall, and an inner
(cytoplasmic) membrane. The outer membrane contains lipopolysaccharides and special
proteins that form pores, allowing small molecules to enter while keeping harmful substances
out. The peptidoglycan layer provides strength and maintains the cell’s shape. The inner
membrane contains many proteins involved in transport and energy production. The space
between the two membranes is called the periplasmic space.
Inside the inner membrane is the cytoplasm, which is a highly concentrated solution of
proteins and other molecules. It contains more than 2,000 different types of proteins that
perform various functions. The amounts of these proteins change depending on
environmental and growth conditions. Although proteins can easily stick together, most
remain properly folded and separated. However, when foreign proteins are produced in large
amounts, they may form inactive clumps known as inclusion bodies.
The cytoplasm also contains the cell’s DNA and many ribosomes. Ribosomes are made of
RNA and protein and are responsible for protein synthesis. In bacteria, DNA is not enclosed
