Biology
Subject Code: LS1001/2-0-0
Syllabus
Cell theory, Structure and function of Prokaryotic and Eukaryotic cell, Cell
division, Cell cycle, Structure and function of Proteins, Carbohydrates, Lipids,
and Nucleic acids, Central dogma of Molecular Biology – DNA replication,
Transcription and Translation, Disease Biology, Applied Biology.
Cell – basic unit of life
What is a Cell?
• Cell is a basic structural, functional and biological unit of all living organisms
(Unicellular and multicellular)
• Term originated from Latin Word “Cella” meaning small room and discovered
by
Robert Hooke in 1665 while studying cork under microscope
Robert Hooke
Microscope
Cells of Cork
• It is a self-replicating structures that can respond to changes in the
environment and often called building block of life
• Study of cell is called cell biology
Robert Hooke published findings about Cells in his book entitled Micrographia in
which he gave 60 ‘observations of various objects under a coarse, compound
microscope
One observation was from very thin slices of bottle cork
Hooke did not know their real structure or function
He had thought that cells were actually empty cell walls of plant tissues
With microscopes of low magnification at that time, Hooke was unable to see
internal components of the cells he was observing
So, he thought cells were dead and his observations gave no indication of the
nucleus and other organelles found in most living cells
Anton van Leeuwenhoek is another scientist who saw cells soon after Hooke did
He made use of a microscope containing improved lenses that could magnify
objects almost 300-fold
Under these microscopes, Leeuwenhoek found motile objects and he states that
motility is a quality of life therefore these were living organisms
Over time, he wrote many more papers in which described many specific forms of
microorganisms like bacteria and protozoa
The cells in animal tissues were observed after plants were because the tissues
were so fragile and susceptible to tearing, it was difficult for such thin slices to be
prepared for studying
Biologists believed that there was a fundamental unit to life, but were unsure what
this was
It would not be until over a hundred years later that this fundamental unit was
connected to cellular structure and existence of cells in animals or plants
This conclusion was not made until Henri Dutrochet who besides stating, “the cell
is the fundamental element of organization”, also claimed that cells were not just
a structural unit, but also a physiological unit
In 1804, Karl Rudolphi and J.H.F. Link were awarded the prize for "solving the
problem of the nature of cells", meaning they were the first to prove that cells had
independent cell walls by the Königliche Societät der Wissenschaft (Royal Society
of Science), Göttingen
Later in 1838 concept of cell theory came into existence
Cell – Important Features
• Grow
• Repair and Maintain
• Reproduce
• Undergo change
• Move
• Respond
• Grow old and die
Why basic unit of life - Smallest of biological structure that perform all basic
activities of life
Cellular Hierarchy
Organism (Human)
Organ-system (Respiratory system)
Organ (Lung)
Tissue (Epithelial tissue)
Cells
Cell (Monocyte)
Cell Theory
In biology, cell theory is a scientific theory which describes the properties of cells
Cell theory is the foundation of biology and is the most widely accepted
explanation of the function of cells
With continual improvements made to microscopes over time, magnification
technology advanced enough to discover cells in the 17th century
After the discovery of cells, many debates started about properties, role and
function of cells
Eventually in 1838, Cell theory was formulated by Matthias Schleiden and Theodor
Schwann. Other scientists like Rudolf Virchow also contributed to the theory
Schleiden suggested:
1. Cells or result of cells contribute to structural part of a plant
2. Cells are made by a crystallization process either within other cells or from the
outside
Schwann suggested:
1. Like plants, structurally animals are composed of cells or the product of cells
The following are the three basic principles to this cell theory:
1. All living organisms are composed of one or more cells
2. The cell is the most basic unit of life
3. All cells arise from pre-existing, living cells (Contributed by Rudolf Virchow in
1855)
Essential features of Cell Theory
Following are the essential features of cell theory:
1. Cells are fundamental units of structure and function in all living organisms
2. Cells are physiological units of living organisms
3. Cells are hereditary units
4. New cells originate from the pre-existing cells only
5. Cell is the smallest unit of life. All activities of living organisms are the outcome
of the activities of its constituent cells
Diversity in Cell size
Diversity exists in the cells as far as size, shape and number is concerned
Most cells are microscopic, visible only under the high power of microscope
Size varies greatly from 80 milli micron to a meter
Nerve cells are the longest
Egg of Ostrich is about 175x135 mm
In human body cell size ranges between 3-4 micron (Leukocytes) to over 90 cm
(nerve cells)
The nucleo-cytoplasmic ratio and surface area are the two important factors that
restrict the cell size
Diversity in Cell shape
The shape of the cells is related to their functions
Some blood cells and Amoeba change their shape whereas others have constant
shape
The cells may be spherical, oval, rounded or elongated, cuboidal, cylindrical,
tubular, polygonal, plate-like, discoidal or irregular
The cell shape is influenced by :
1. Surface tension and viscosity of the protoplasm
2. Mutual pressure of the surrounding cells
3. Rigidity of the cell membrane
4. Internal environment and function of the cell
Types of cells
Cells are generally three types:
1. Prokaryotic:
Relative simple cells with no membrane bound organelles like RE, Golgi
complex, mitochondria, chloroplast or lysosomes. The hereditary material is
highly coiled circular chromosome lying naked in the cytoplasm. It is formed of
DNA alone and called nucleoid like Bacteria and blue green algae
2. Eukaryotic:
These cells contain a true nucleus. Hereditary material that is DNA is
associated with basic proteins and forms nucleoprotein separated from
cytoplasm by nuclear envelop. Membrane bound organelles are present like
plant and animal cells.
3. Mesokaryotic:
In these cells nuclear membrane is present around the nucleus but DNA is not
associated with histones. These cells are more advance than prokaryotes and
less advance than eukaryotes like Dinoflagellates
Structure of Eukaryotic and Prokaryotic cells