BSCBO-
301
B.Sc. III YEAR
Cell Biology, Molecular Biology
And
Biotechnology
DEPARTMENT OF BOTANY
SCHOOL OF SCIENCES
UTTARAKHAND OPEN UNIVERSITY
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BSCBO- 301
B.Sc. III YEAR
Cell Biology, Molecular Biology
And
Biotechnology
DEPARTMENT OF BOTANY
SCHOOL OF SCIENCES
UTTARAKHAND OPEN UNIVERSITY
BSCBO-
CELL BIOLOGY, MOLECULAR BIOLOGY AND
BIOTECHNOLOGY
SCHOOL OF SCIENCES DEPARTMENT OF BOTANY UTTARAKHAND OPEN UNIVERSITY
Phone No. 05946-261122, 261123
Toll free No. 18001804025
Fax No. 05946-264232, E. mail info@uou.ac.in
htpp://uou.ac.in
Unit Written By: Unit No.
1. Dr. Atal Bihari Bajpai 1 & 2 Associate Professor, Department of Botany, DBS PG College, Dehradun
2 - Dr. Nishesh Sharma 3, 4, 5, 6, 7 & 8 Asst. Professor, Department of Biotechnology, Uttaranchal College of Applied and Life Science Uttaranchal University, Dehradun
3-Dr. Anil Bisht 9, 10, 11 & 12 Asst. Professor, Department of Botany, DSB Campus, Kumaun University, Nainital
Course Editor
Dr. Gulshan Kumar Dhingra Associate Professor, Department of Botany Pt. LMS PG College Rishikesh, Uttarakhand
Title : Cell Biology, Molecular Biology and Biotechnology ISBN No. : 978-93-90845-38- Copyright : Uttarakhand Open University Edition : 2021
Published By: Uttarakhand Open University, Haldwani, Nainital-
CONTENTS
BLOCK-1 CELL BIOLOGY PAGE NO.
Unit-1 The Cell 6- 44
Unit-2 Structures and Functions of Cell Organelles 45-
Unit-3 Structure and Types of Chromosomes 85-
Unit-4 Cell Division 115-
BLOCK-2 MOLECULAR BIOLOGY PAGE NO.
Unit -5 Structure and Composition of DNA 146-
Unit-6 Structure and Composition of RNA 179-
Unit-7 Modern Concept of Gene and Genetic code 208-
Unit-8 Protein synthesis and Gene regulation of Protein synthesis 246-
BLOCK-3 BIOTECHNOLOGY PAGE NO.
Unit-9 Recombinant DNA 278-
Unit-10 Genetic Engineering 315-
Unit-11 Biotechnology 350-
Unit-12 Plant Tissue Culture 378-
UNIT-1THE CELL
1.1-Objectives 1.2-Introduction 1.3-Historical background 1.4-Cell theory 1.5- Size and structure of cell 1.6-Prokaryotic and Eukaryotic cell 1.7- Glossary 1.8-Self Assessment Question 1.9- References 1.10-Suggested Readings 1.11-Terminal Questions
1.1 OBJECTIVES
After reading this unit student will be able to understand about- the advancements in cell biology brief idea about the great diversity shown by cells in their shapes and sizes Also, to give an outline information about structures and purposes of basic components of prokaryotic and eukaryotic cells. to know how the cellular components are arranged in both types of cell.
1.2 INTRODUCTION
The basic structural and functional unit of cellular organization is the cell. Within a selective and relative semi permeable membrane, it contains a complete set of different kinds of units necessary to permit its own growth and reproduction from simple nutrients. All organisms, more complex than viruses, consist of cells, yet they consist of a strand of nucleic acid, either DNA or RNA, surrounded by a protective protein coat (the capsid). The word cell is derived from the Latin word cellula , which means small compartment. Hooke published his findings in his famous work, Micrographia. Actually, he only observed cell walls because cork cells are dead and without cytoplasmic contents. A.G. Loewy and P. Siekevitz have defined cell as ― A unit of biological activity delimited by a semi permeable membrane and capable of self reproduction in a medium free of other living organisms ‖. John Paul has defined the cell as ―The simplest integrated organization in living systems, capable of independent survival‖.
On the basis of internal organization and architecture, all cells can be subdivided into two major classes, prokaryotic cells and eukaryotic cells. Cells which have the unit membrane bound nuclei are called eukaryotic, whereas cells that lack a membrane bound nucleus are prokaryotic. Besides the nucleus, the eukaryotic cells have other membrane bound organelles (small organs) like the Endoplasmic reticulum, Golgi complex, Lysosomes, Mitochondria, Microbodies and Vacuoles. The prokaryotic cells lack such unit membrane bound organelles.
1.3 HISTORICAL BACKGROUND
Ancient Greek philosophers such as Aristotle 384-322 B.C and Paracelsus concluded that ― All animals and plants, however, complicated, are constituted of a few elements which are repeated in each of them ‖. They were referring to macroscopic structures of an organism such as roots, leaves and flowers common to different plants, or segments and organs that are repeated in the animal kingdom. Many centuries later, owing to the invention of magnifying lenses, the world of microscopic dimensions was discovered. Da Vinci (1485) recommended the uses of lenses in viewing small objects. In 1558, Swiss biologist, Conard Gesner (1516-1565) published results on
1.4 CELL THEORY
In biology, cell theory is a scientific theory which describes the properties of cells. These cells are the basic unit of structure in all organisms and also the basic unit of reproduction. With continual improvements made to microscopes over time, magnification technology advanced enough to discover cells in the 17th century. This discovery is largely attributed to Robert Hooke, and began the scientific study of cells, also known as cell biology. Over a century later, many debates about cells began amongst scientists. Most of these debates involved the nature of cellular regeneration, and the idea of cells as a fundamental unit of life.
Fig.1.2 Mathias Jakob Schleiden (1804–1881) Fig.1.3 Theodor Schwann (1810–1882)
Matthias Jakob Schleiden (5 April 1804 – 23 June 1881) was a German botanist and co- founder of cell theory, along with Theodor Schwann (7 December 1810 – 11 January 1882) a German physiologist and Rudolf Ludwig Carl Virchow (13 October 1821 – 5 September 1902) was a German physician, anthropologist, pathologist, prehistorian, biologist, writer, editor, and politician, known for his advancement of public health. Credit for developing cell theory is usually given to these scientists- Schleiden and Schwann. While Rudolf Virchow contributed to the theory, he is not as credited for his attributions toward it. In 1838, Schleiden suggested that every structural part of a plant was made up of cells or the result of cells. He also suggested that cells were made by a crystallization process either within other cells or from the outside. However, this was not an original idea of Schlieden. He claimed this theory as his own, though Barthelemy Dumortier had stated it years before him. This crystallization process is no longer accepted with modern cell theory. In 1839, Theodor Schwann states that along with plants, animals are composed of cells or the product of cells in their structures. This was a major advancement in the field of biology since little was known about animal structure up to this point
compared to plants. From these conclusions about plants and animals, two of the three tenets of cell theory were postulated.
- All living organisms are composed of one or more cells.
- The cell is the most basic unit of life. Schleiden's theory of free cell formation through crystallization was refuted in the 1850s by Robert Remak, Rudolf Virchow, and Albert Kolliker. Robert Remak (26 July 1815 – 29 August
- was a Jewish Polish-German embryologist, physiologist, and neurologist, born in Posen, Prussia, who discovered that the origin of cells was by the division of pre-existing cells. In 1855, Rudolf Virchow added the third tenet to cell theory. In Latin, this tenet states " Omnis cellula e cellula ". This translated to-
- All cells arise only from pre-existing cells. However, the idea that all cells come from pre-existing cells had in fact already been proposed by Robert Remak; it has been suggested that Virchow plagiarized Remak and did not give him credit. Remak published observations in 1852 on cell division, claiming Schleiden and Schawnn were incorrect about generation schemes. He instead said that binary fission, which was first introduced by Dumortier, was how reproduction of new animal cells was made. Once this tenet was added, the classical cell theory was complete. Barthélemy Charles Joseph Dumortier (3 April 1797 in Tournai – 9 June 1878) was a Belgian who conducted a parallel career of botanist and Member of Parliament.
Modern Interpretation
The generally accepted parts of modern cell theory include:
1- All known living things are made up of one or more cells. 2- All living cells arise from pre-existing cells by division. 3- The cell is the fundamental unit of structure and function in all living organisms. 4- The activity of an organism depends on the total activity of independent cells. 5- Energy flow (metabolism and biochemistry) occurs within cells. 6- Cells contain DNA which is found specifically in the chromosome and RNA found in the cell nucleus and cytoplasm. 7-All cells are basically the same in chemical composition in organisms of similar species.
The modern version of the cell theory :
The modern version of the cell theory includes the ideas that: 1- Energy flow occurs within cells. 2- Heredity information (DNA) is passed on from cell to cell. 3- All cells have the same basic chemical composition.
Fig.1.5 : Several different types of cells all referenced to a standard E. coli ruler of 1 micron (A) The protist Giardia lamblia , (B) a plant cell, (C) a budding yeast cell, (D) a red blood cell, (E) a fibroblast cell, (F) a eukaryotic nerve cell, and (G) a rod cell from the retina.
Cell Size
One may wonder why all cells are so small. If being able to store nutrients, is beneficial to the cell, how come there are no animals existing in nature with huge cells? Physical limitations prevent this from occurring. A cell must be able to diffuse gases and nutrients in and out of the cell. A cell's surface area does not increase as quickly as its volume, and as a result a large cell may require more input of a substance or output of a substance than it is reasonably able to perform. Worse, the distance between two points within the cell can be large enough that regions of the cell would have trouble communicating, and it takes a relatively long time for substances to travel across the cell. That is not to say large cells don't exist. They are, once again, less efficient at exchanging materials within themselves and with their environment, but they are still functional. These cells typically have more than one copy of their genetic information, so they can manufacture proteins locally within different parts of the cell. Features of such large cells are following:
- Is limited by need for regions of cell to communicate
- Diffuse oxygen and other gases
- Transport of mRNA and proteins
- Surface area to volume ratio limited
Larger cells typically: a) Have extra copies of genetic information b) Have slower communication between parts of cell
Fig. 1.6- Various types of cells ranging in different sizes
The shapes of cells are quite varied with some, such as neurons, being longer than they are wide and others, such as parenchyma (a common type of plant cell) and erythrocytes (red blood cells) being equidimensional. Some cells are encased in a rigid wall, which constrains their shape, while others have a flexible cell membrane (and no rigid cell wall). The size of cells is also related to their functions. Eggs (or to use the Latin word, ova) are very large, often being the largest cells an organism produces. The large size of many eggs is related to the process of development that occurs after the egg is fertilized, when the contents of the egg (now termed a zygote) are used in a rapid series of cellular divisions, each requiring tremendous amounts of energy that is available in the zygote cells. Later in life the energy must be acquired, but at first a sort of inheritance/trust fund of energy is used. Cells range in size from small bacteria to large, unfertilized eggs laid by birds and dinosaurs. Here are some measurements and conversions that will aid your understanding of biology.
1 meter = 100 cm = 1,000 mm = 1,000,000 μm = 1,000,000,000 nm 1 centimeter (cm) = 1/100 meter = 10 mm 1 millimeter (mm) = 1/1000 meter = 1/10 cm 1 micrometer (μm) = 1/1,000,000 meter = 1/10,000 cm 1 nanometer (nm) = 1/1,000,000,000 meter = 1/10,000,000 cm
2. Shape of Bacteria: The three basic bacterial shapes are: Cocci – (spherical shaped). e.g., Diplococcus pneumonia, Streptococcus pyogenes etc. Bacilli – (rod-shaped) e.g. Mycobacterium, Clostridium botylinum etc. Spirilla (spiral or twisted) e.g. Treponema pallidum etc However pleomorphic bacteria can assume several shapes.
Fig. 1.8 Different shapes of bacteria
3. Structure of Bacteria: (i) Plasma membrane- It is an ultra thin membrane 6-8 nm thick, chemically comprised of molecules of lipids and proteins, arranged in a fluid mosaic pattern. Infoldings in it gives rise to two main types of structures: (a) Mesosomes- (Also known as Chondriods); are extensions involving complex whorls of convoluted membranes. They increase surface area of plasma membrane and enzymatic contents. (b) Chromatophores- These are photosynthetic pigment- bearing membranous structures of photosynthetic bacteria and are present as vesicles, thylakoids, tubes etc.
(ii) Cell Wall- It is strong and rigid and covers plasma membrane to provide chemical protection and characteristic shape of bacteria. It is made up of peptidoglycan and contains muramic acid.
(iii) Capsule- In some bacteria, cell wall is surrounded by an additional slime or gel layer called capsule that acts as protective layer against viruses and phagocytes.
(iv) Cytoplasm - It is the ground substance surrounded by plasma membrane and is site of all metabolic activities of bacteria. It consists of water, proteins, enzymes, different types of RNA molecules and reserve materials like glucogen, volutin and sulphur. The dense nuclear areas of cytoplasm contain 70S ribosomes granules, composed of RNA and protein and are the site of protein synthesis.
(v) Nucleoids- The nuclear membrane includes a single, circular and double stranded DNA molecule often called as bacterial chromosome. It is not separated by nuclear membrane and is usually concentrated in a specific clear region of the cytoplasm called nucleoid. It has no ribosomes, nucleolus and histone proteins.
(vi) Plasmids – Many species of bacteria may also carry extrachromosomal genetic elements in the form of small, circular, and closed DNA molecules called plasmids. They produce antibiotically active protein or colicins which inhibit the growth of other bacterial strain in their vicinity. They may also act as sex or fertility factors (F factor) which stimulate bacterial conjugation. R factors are also plasmid carrying genes for resistance to drugs.
(vii) Flagella- Many bacteria are motile and contain one or more flagella for cellular locomotion. They are 15-20nm in diameter and up to 20μm long. e.g., E.coli etc
4. Nutrition: They show diversity in their nutrition from being chemosynthetic, to photosynthetic; but most of them are heterotrophic. Heterotrophic bacteria are mostly either saprophytic or parasitic. Parasitic lives on the bodies of other organisms. Most bacteria are pathogenic. 5. Mode of Respiration: It is of both types; aerobic (which respire in the presence of oxygen.eg Lactobacillus ) and anaerobic (which respire in the absence of oxygen. e.g. Pseudomonas ). 6. Reproduction: Bacteria reproduce through asexually by binary fission and endospore formation and sexually by conjugation. In conjugation, genetic exchange and recombination occurs through sex pili, but this is a form of horizontal gene transfer and is not a replicative process, simply involving the transference of DNA between two cells.
B: Eukaryotic Cell
The Eukaryotic cells are essentially two envelope systems and they are very much larger than prokaryotic cells. Secondary membranes envelop the nucleolus and other internal organelles and to a great extent they pervade the Cytoplasm as the Endoplasmic reticulum. The Eukaryotic cells are true cells which occur in the plants (from algae to angiosperms) and the animal (from Protozoa to mammals). Though the Eukaryotic cells have different shape, size, and physiology; all the cells are typically composed of plasma membrane, cytoplasm and its organelles, viz. Mitochondria, Endoplasmic reticulum, ribosomes, Golgi apparatus etc; and a true nucleus. Here
3. Cell Volume: The volume of cell is fairly constant for a particular cell type and is independent of the size of the organism ( Law of Constant Volume ). For example, kidney or liver cells are about the same size in the bull horse and mouse. The difference in the total mass of organ depend upon the number not on the volume of the cells. If a cell is to be efficient, the ratio of volume to surface should be within a limited range. An increase in the cell volume is accompanied by much smaller expansion in surface area of the cells. In other words, a large cell has a proportionately smaller surface area and a higher volume: Surface ratio than a small a cell. 4. Cell Number: The number of cell present in organism is varies from a single cell in unicellular organism to many cell in multi cellular organism. The number of cell in multicellular organism usually remains correlated with the size of organism and, therefore, a small sized organism has a less number of cells in comparison to large sized organism. Further, the number of cells in most of multicellular organism is indefinite, but the number of cells may be fixed in some multicellular organism. For example, in rotifers, numbers of nuclei in the various organs are found to be constant in any given species. The phenomenon of cells or nuclear constancy is called Eutely. In one species of rotifers, Martini (1912) always found 183 nuclei in the brain, 39 in stomach and so on. 5. Structure: (i) Cell Wall: The outermost structure of most plant cells is a dead and rigid layer called cell wall. It is mainly composed of carbohydrates such as cellulose, pectin hemicelluloses and lignin and certain fatty substances like waxes. There is pectin- rich cementing substance between the walls of adjacent cells which is called middle lamella. The cell wall which is formed immediately after the division of cell, constitute the primary cell wall. In certain types of cells such as phloem and xylem, an additional layer is added to the inner surface of primary cell wall called, secondary cell wall and it consist mainly of cellulose, hemicelluloses and lignin. In many plant cells, there are tunnels running through the cell wall called Plasmodesmata which allow communication with the other cells in a tissue.
(ii) Plasma Membrane: Every kind of animal cell is bounded by a living, extremely thin and delicate membrane called Plasma lemma, cell membrane or plasma membrane. In plant calls plasma membrane occurs just inner to cell wall, bounding the cytoplasm. The plasma membrane exhibits a tri- laminar structure with a translucent layer sandwiched between two dark layers. The plasma membrane is selectively permeable membrane; its main function is to control selectively the entrance and exit of materials. This allows then cell to maintain a constant internal environment (Homeostasis). Molecules of water, oxygen, carbon-dioxide, glucose etc., are transported across the plasma membrane takes place by various means such as osmosis, diffusion, and active transportation.
(iii) Cytosol: The plasma membrane is followed by the colloidal organic fluid called matrix or cytosol. The cytosol is aqueous part of cytoplasm and nucleoplasm. Cytosol is particularly rich in differentiation cells and many fundamental properties of cells are because of this part of cytoplasm. The cytosol serves to dissolve or suspend the great verity of small molecules concerned with cellular metabolism, e.g., glucose amino acids, nucleotides, vitamins, minerals, oxygen. In all type of cells, cytosol contains the soluble proteins and enzymes which form 20- % of the total protein content of the cells. In many types of cells, the cytosol is differentiated into two parts: (a) Ectoplasm or cell cortex is the peripheral layer of cytosol which is relatively non granular, viscous, clear and rigid. (b) Endoplasm is the inner portion of cytosol which is granular and less viscous.
Cytoskeleton and Microtrabecular Lattice
The cytosol of cells also contains fibers that help to maintain cell shape and mobility and that probably provide anchoring points for the other cellular structures. These fiber‘s are called cytoskeleton. At least three general classes of such fibers have been identified. 1-The thickest are the microtubules (20 nm in diameter) which consists primarily of the tubulin protein. The function of microtubules is the transportation of water, ions or small molecules, cytoplasmic streaming (cyclosis), and the formation of fibers or asters of the mitotic or meiotic spindle during cell division. 2-The thinnest are the microfilaments (7mm in diameter) which are solid and are solid and are principally formed of actin protein. 3-The fibers of middle order are called the intermediate filaments (Ifs) having a diameter of 10nm. They have been classified according to their constituent protein such as desmin filaments, keratin filament, Neurofilaments, vimentin and glial filaments.
(i) Cytoplasmic structures: In the cytoplasmic matrix certain non living and living
structures remain suspended. The non living structures are called paraplasm and inclusion, while the living structures can be studied under the following headings:
Cytoplasmic Inclusion
The stored food and secretory substances of the cell remain suspended in the cytoplasmic matrix in the form of refractile granules forming the cytoplasmic inclusion. The cytoplasmic inclusion involves oil drops, yolk granules, triacylglyerol and starch grains.
Cytoplasmic Organelles
Besides the separates fibrous systems cytoplasm is coursed by a multitude of internal membranous structures, the organelles. Cytoplasmic organelles performed specialized tasks: Generation of energy in the form of ATP molecules in Mitochondria; formation and storage of