a) Introduction to cell biology
The cell biology
is the biological science which deals with the study of structure, function,
molecular organization, growth, reproduction and genetics of the cell, is
called cell biology. In 1865 the term cell was first time used by Robert Hook. It seems to be the
principle of nature that where there is diversity, there is also similarity.
Indeed, nature’s variety is boundless. When walking through the woods, across a
field, along a stream, thorough a zoo or wild life sanctuary, one is impressed
with the diversity of life. Even looking through a microscope can be an elating
experience. The universe of the cell too is complex and diverse. Like the world
around us, the world of the cell is one of the forms specialized for a
particular type of existence. And as is in the large universe of the plant and
animal kingdoms, where one can perceive basic life sustaining processes common
to all organisms, in the cellular world many of the same processes and
structure can be found in almost all cells. This generalization often leads to
one of the most fundamental and obvious statement that the cell is the
microscopic structural and functional unit of the living organisms. Thus, there
are many cells types among fungi, protozoan and higher plants and animals. They
differ in size, forms and functions, degree of specialization and average
generation time. Yet at the ultra-structural level there is sameness about
cells that is almost tedious. The same basic structures- nuclei, cytoplasmic
matrix, plastids, mitochondria, endoplasmic reticulum, Golgi apparatus and
plasma membrane etc. all appear with predictable regularity. Such sameness can
also be observed at the molecular level- all cell parts are made of highly
organized groups of few types of molecules like proteins, lipids, carbohydrates
and nucleic acids etc.
b) Introduction
to molecular biology
The term
molecular biology was first used in 1945 by William Astbury who was referring to the study of the chemical and
physical structure of biological macromolecules. By that time, biochemist had
discovered many fundamental intracellular chemical reactions. The importance of
specific reactions and of protein structure in defining the numerous properties
of cells was also appreciated. However, the development of molecular biology had
to await the understanding that the most advantageous approaches would be made
by studying ‘simple’ system such as bacteria and bacteriphages which yield
information about the basic biological processes more readily than animal
cells. In fact, the faith in the basic uniformity of life processes was an
important factor in rapid growth of molecular biology. That is, it was believed
that fundamental biological principles that govern the activity of simple
organisms, such as bacteria and viruses, must apply to more complex cells; only
the details should vary. This faith has been amply justified by experimental
results.
The roots of
molecular biology were established in 1953 when as Englishmen, Francis Crick
and young American, James Watson working at Medical Research Council Unit,
Cavendish Laboratory, Cambridge proposed a double helical model for the
structure of DNA molecule which was well known as the chemical bearer of
genetic information of certain microorganisms like bacteria and bacteriophage
etc. due to pioneer discoveries made by Grifith (1928), Avery, Macleod and
McCarty (1944) and Hershey and Chase (1952). This discovery was followed by a
thorough search of occurrence of DNA as the genetic material in other
microorganisms, plants and animals and also by investigations of the molecular
and atomic nature of different reactions of living cells. From all these
studies has emerged the realization that the basic chemical organization and
the metabolic processes of all living things are remarkably similar despite
their morphological diversity and that the physical and chemical principles
governing living systems are similar to those governing non-living systems.
The present
understanding of molecular biology is that in most organisms the phenotype or
the body structure and function ultimately depend for their determination on
the structural and functional proteins or polypeptides (enzymes). The synthesis
of proteins is specified, directed and regulated by self duplicating genes
which are borne within molecules of DNA which is the universally accepted
chemical bearers of genetic information’s of most living organism except
certain viruses in which this function is carried by another nucleic acid, the
RNA. The genetic information for
polypeptide synthesis is initially directed by the disposition of nitrogen
bases in DNA molecule and is copied down by the process of transcription. During transcription stage copies of an individual
gene or genes are synsthesized. These copies are molecules of RNA that include
such similar classes as rRNA, mRNA and tRNA. The biochemical interplay of these
RNA copies which leads to the synthesis of a polypeptide chain is called translation. It literally means the
genetic message encoded in a mRNA molecule is translated into the linear
sequence of amino acids in a polypeptide. The polypeptide in its turn
determines the phenotype of the organism.
Exercise
Q.
1 A) Multiple choice questions (1 mark each)
1. ……..
is the structural and functional unit of life
a. Cell b. Tissue c. Organ d.
None
2. The term molecular biology was first used in
1945 by …….
a.
William Bateson b. William Astbury c.
Robert Hooke d. Robert Brown
3. The
term cell was used by ……….
a.
H. Janssen b. B. Lamarck c. R. Brown d. R. Hooke
Q.
1 B) Answer in one sentences (1 mark each)
i. Write the name of molecule, known for
chemical bearer of genetic information.
ii. Who establishes roots of molecular
biology
iii. Who proposed a double stranded helical
model of DNA
iv. Which determines the phenotype of the
organisms
Q.2.
Define/ Explain/ Comments (2 mark each)
i. Cell
biology
ii. Molecular
biology
iii. Transcription.
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