Cell - 1
Just as the atom is the fundamental unit of matter, the cell is the fundamental
unit of living organisms.
Each cell is unique, composed of carbohydrates, proteins,
lipids, and other substances, organized into an orderly structural and functional
We shall, in this chapter, see how the structure of cells and, in particular,
the structure of cell components, facilitates the functioning of cells.
History of the cell
The study of cells dates back more than three hundred years, coinciding with the
development of microscopes.
As scientists over the years learned more about
cells, a group of common characteristics was developed which we call the Cell
Our use today of more sophisticated microscopes and research on
biochemical cell activities reinforces these premises.
The Cell Theory
Every living organism is made up of one or more cells.
Cells are the structural and functional unit of living organisms.
living organisms are single cells, and cells comprise the functional units of
All cells arise from preexisting cells.
Basic Cell Features (Common to All Cells)
Plasma (cell) membrane
The plasma membrane is the boundary between the cell and its environment.
The plasma membrane isolates the cell, regulates what enters and leaves the cell,
and allows for interaction with other cells.
The plasma membrane is comprised of
phospholipid layers with proteins embedded throughout.
The diversity of proteins
found within membranes is responsible for most membrane activity. We will
discuss membrane structure and function a bit later.
nucleus or nucleoid
Each cell contains genetic molecules: (DNA), which stores the instructions for that
cell's structure and function, and RNA molecules, which perform a number of
functions in cells, including carrying DNA instructions for protein synthesis.
cell's DNA may be found within a membrane - bounded nucleus, (eukaryotic
organisms – plants, animas, protists and fungi) or simply concentrated in a region
of the cytoplasm called the nucleoid (prokaryotic organisms - Eubacteria and
Whether DNA is within a nucleus or not is a fundamental cell
organizational difference in the classification of life.
Except for its DNA structures, the cytoplasm includes the fluid matrix (called the
cytosol) inside the plasma membrane in which everything else in the cell, such as
internal membranes, particles and membrane-bounded structures, called
organelles, are suspended.