Lecture 1. Cell Biology Basics.pdf

UBT 008: Cell Biology and Genetics Sections Topics Module I Cell Structure and Functions MST [5 weeks]...

UBT 008: Cell Biology and Genetics Sections Topics Module I Cell Structure and Functions MST [5 weeks] Module II Cell Division Module III Genetics EST [5 weeks] Module IV Linkage and Recombination Course Objectives: 1. To imparts knowledge of structural and functional aspects of cells as units of living systems. 2. To understand functions of various organelles and transport of information and matter across cell membrane. 3. To understand Mendelian Laws of Inheritance and their significance in genetic diseases. Course Learning Outcomes: 1. Acquire knowledge about the organizational and functional aspects of cell and organelles. 2. Learn about interaction of cells with outside environment through exchange of information and transport of molecules. 3. Learn about classical genetics and transmission of characters from one generation to the next which will make foundation for advanced genetics. 4. Develop innovative research ideas for curing genetic disorders in human. 06-09-2024 Cell Biology : Basics 1 Books to be Referred for Cell Biology and Genetics 1. Bruce Alberts et al., Essential Cell Biology. Garland Science (Taylor and Francis) 2. Veer Bala Rastogi, Cell Biology (MedTech Science Press) 3. Geoffrey M. Cooper., The Cell: A molecular Approach 4. H. Lodish et al., Molecular Cell Biology (4th Edition), WH Freeman 5. Gardner, Simmons and Snustad, Principle of Genetics by John Wiley and Sons 6. Eddon John Gardner, Principle of Genetics (Wiley, 8th Edition) 7. Peter J. Russel. Genetics: A Molecular Approach (Pearson Education India) Course Instructor: Dr. Jyotsana Mehta Email Id: [email protected] Contact No. 8708290308 06-09-2024 Cell Biology : Basics 2 Module I: Cell Structure and Functions 1. Cell Biology Basics 1.1. Living Organisms : Unicellular and Multicellular Organisms 1.2. Cell: Definitions; Basic Features; Hierarchy 1.3. Cell Theory and Cell Doctrine 1.4. Types of Cells: Based on Size, Shape and Morphology 06-09-2024 Cell Biology : Basics 3  1.1. Living Organisms: Unicellular and Multicellular Organisms  Organism can be broadly defined as a molecule assembly functioning in totality and exhibits properties of life.  Monomeric unit of their existence is called Cell.  Basic parameter of an organism is its life span. Some organisms live for one day, while some plants and fungi can live thousands of years.  Basically made up of complex system of macromolecules.  Macromolecules like carbohydrates, proteins, nucleic acid and lipids play important role in day to day function of the organism. 06-09-2024 Cell Biology : Basics 4  1.1. Living Organisms: Unicellular and Multicellular Organisms Unicellular Organisms Unicellular Multi-cellular  Known as a single-celled organism (Most primitive form of organisms).  Main groups of unicellular organisms are bacteria, archaea, protozoa, algae and fungi.  Fall into two general categories: prokaryotic and eukaryotic organisms (based on cellular organization)  Oldest form of life, possibly existing 3.8 billion years ago.  Mostly these organisms are microscopic (cannot be seen by naked eyes) and categorised as microorganisms.  Examples are: Bacteria like Escherichia coli, Mycobacteria, Bacillus sp. etc. Protozoans like Amoeba, Paramecium etc. Algae like Chlorella sp, Chlamydomonas, Diatoms, Euglenophyta, Dinoflagellates etc; Fungi like yeast. 06-09-2024 Cell Biology : Basics 5  1.1. Living Organisms: Unicellular and Multicellular Organisms Multi-cellular Organisms  Consist of many cells specialized to do different functions for maintaining the complexity of the organism.  Most bacteria are unicellular, but some bacterial species are multicellular like Myxobacteria. Some species of cyanobacteria are also multicellular like Spirogyra etc.  Most eukaryotic organism are multicellular. Multicellular organisms have well developed body structure and also have specific organs for specific function.  Most well developed plants and animals are multicellular. All animals are eukaryotic in nature and most of them are multicellular. In plants highly evolved types like angiosperms and gymnosperms are multicellular. Examples of unicellular plants are Chlamydomonas ( green algae), chlorella (single-celled green algae), etc. Acetabularia is the largest unicellular green algae. It reaches to the size 0.5 to 10 cm in length.  Cell divisions is essential for three major functions in multicellular organisms: Growth, Development, and Repair.  Two types of divisions are present: Mitosis (Vegetative Divisions) and Meiosis (Reductive Cell division). 06-09-2024 Cell Biology : Basics 6  Differences between Unicellular and Multicellular Organisms Unicellular Organisms Multicellular Organisms  Body is made up of single cell  Body is made up of numerous cells  Division of labour may be at cellular, tissue,  Division of labour is at the organelle level. It organ and organ system level. It gives high gives a low level of operational efficiency. degree of operational efficiency.  Different cells are specialized to perform  A single cell carries out all the life processes different functions.  Only outer cells are specialized to face the  The cell body is exposed to the environment environment. Inner cells are devoted to other on all sides. functions. 06-09-2024 Cell Biology : Basics 7 Contd………  Unicellular Organisms Multicellular Organisms  Injury or death of some cells does not affect  An injury to the cells can cause death of the the whole organism as the same can be organism. replaced by new one.  Cell body cannot attain a large size  A multicellular body can attain a large size because of the limit imposed by surface increasing the number of small cells. area to volume ratio.  Lifespan is long due to limited load of work  Lifespan is short due to heavy load of work. for each cell type.  Certain specialized cells lose power of  Power of division is not lost. division.  The capacity of regeneration decreases with  Capacity of regeneration present. increasing specialization. 06-09-2024 Cell Biology : Basics 8  Common Features of Unicellular and Multi-cellular Organisms All organisms must accomplish the same functions:  uptake and processing of nutrients  excretion of wastes  response to environmental stimuli  reproduction among others 06-09-2024 Cell Biology : Basics 9  1.2. Cell: Definitions; Basic Features; Hierarchy 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 “Cellula” or “Cellus” meaning small room or little space and was discovered by Robert Hook in 1665 while studying cork under microscope. Robert Hook Microscope Cells of Cork  It is a self-replicating structures that are capable of responding to changes in the environment.  Often called building block of life.  Study of cell is called cell biology. 06-09-2024 Cell Biology : Basics 10  1.2. Cell Theory  Robert Hook published findings about Cells in his book entitled Micrographia in which he gave 60 ‘observations of various objects under an optical microscope’.  One observation was from very thin slices of bottle cork (tiny empty boxes/hexagonal dimensions). 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.  Antonie 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 stated 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. He called these tiny creatures “animalcules.”  He also gave accurate description of red blood cells, sperm cells, fertilization process and thus, ended the theory of spontaneous generation. 06-09-2024 Cell Biology : Basics 11  1.2. Cell: Definitions; Basic Features; Hierarchy  The cells in animal tissues were observed after plants 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.  Henri Dutrochet was the first person to state that “the cell is the fundamental element of organization”, he 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. Prior to that, it was though that cells shared cell wall and fluid passed between them.  Later in 1838 concept of cell theory came into existence. 06-09-2024 Cell Biology : Basics 12  1.2. 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 06-09-2024 Cell Biology : Basics 13  1.2. Cellular Hierarchy Organism (Human) Organ-system (Respiratory system) Organ (Lung) Tissue (Epithelial tissue, interstitial connective tissue, and lymphoid tissue Cells Cell (Monocyte) 06-09-2024 Cell Biology : Basics 14  1.3. 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 regarding the structural and functional aspects 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 1838-1839, Cell theory was formulated by Matthias Schleiden and Theodor Schwann. Other scientists like Rudolf Virchow also contributed to the theory. 06-09-2024 Cell Biology : Basics 15  1.3. Cell Theory Schleiden suggested:  Cells or result of cells contribute to structural part of a plant.  Cells are made by a crystallization process either within other cells or from the outside. Schwann suggested:  Like plants, structurally animals are also composed of cells or a group of cells/products of cells. The following are the basic principles of the cell theory: 1. All living organisms are composed of one or more cells. 2. The cell is the most basic unit of life. 06-09-2024 Cell Biology : Basics 16  1.3. 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. Cell is the smallest unit of life. All activities of living organisms are the outcome of the activities of its constituent cells. 06-09-2024 Cell Biology : Basics 17 Significance of Cell Theory  Concept of cell theory emphasizes the structural and functional relationship among the diverse living forms from bacteria to man.  All cells irrespective of their function and position have a nucleus embedded in the cytoplasm and bounded by cell membrane (unity in their structural plan).  Same metabolic processes occur in all the cells primitive or specialized (unity of function).  This implies that all the living things have originated from the same primitive ancestral types that originated billion years ago. Exceptions to the Cell Theory  Viruses are the exception to cell theory because they are made up of proteins and one of the nucleic acid (DNA or RNA), lack protoplasm.  Bacteria lack well-organised nucleus. Nuclear membrane, nucleolus and nucleoplasm are also absent. Nucleic acid (DNA) alone forms the chromosome and lies in direct contact with cytoplasm. Basic proteins associated with nucleic acid are absent in bacteria.  Coenocytic hyphae of Rhizopus and cells of Vaucheria are multinucleate. 06-09-2024 Cell Biology : Basics 18  1.3. Objections to Cell Theory 06-09-2024 Cell Biology : Basics 19  1.3. Cell Principle or Cell Doctrine  Such objections necessitated modification of Cell theory.  The modified form of cell theory is described as “Cell Principle or Cell doctrine” Events that led to the development of Cell Principle or Cell Doctrine  In 1858, a German biologist Rudolph Virchow found that all living cells arise from pre-existing cells (“omnis cellula e cellula”)  In 1866, Ernst Haeckel suggested that nucleus might store and transmit the hereditary information.  The improvement made in the field of microscopes and techniques for the study of cells, enabled scientists to collect enormous information on the structural and functional organisation of cells.  As a result of these developments, the cell theory had to be modified and cell principle was formulated. 06-09-2024 Cell Biology : Basics 20  1.3. Important Features of Cell Principle 06-09-2024 Cell Biology : Basics 21  1.3. Important Features of Cell Principle 06-09-2024 Cell Biology : Basics 22  1.3. Cell Theory versus Cell Principle Cell principle is better than cell theory because: 1. It is applicable to all the cells present in living things like plants, animals and micro-organisms 2. Cell principle incorporates all the modern findings related to a cell 06-09-2024 Cell Biology : Basics 23  1.4. Diversity in Cell Size and Shape  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.  Micrometre is usually used to measure the cell-size. Majority of cells are 5-15 micrometer in size [RBCs are 5-8 micrometer].  Nerve cells are the longest (1-2 m in humans).  Egg of Ostrich is about 175 mm x 135 mm.  In human body, cell size ranges between 3-4 micron (Leukocytes) to over 90-100 cm (nerve cells).  The nucleo-cytoplasmic ratio and surface area are the two important factors that restrict the cell size. 06-09-2024 Cell Biology : Basics 24  1.4. Diversity in Cell Size and 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 size and shape is influenced by : 1. Surface area to volume ratio 2. Nucleocytoplasmic ratio 3. Rate of cellular activity 4. Cell association 06-09-2024 Cell Biology : Basics 25  1.4. Diversity in Cell Size and Shape 06-09-2024 Cell Biology : Basics 26  1.4. Diversity in Cell Size and Shape: Influencing Factors 1. Surface Area to Volume Ratio  The interior content of the cell is separated from the external environment by the cell membrane. This distinction, however, does not imply isolation.  The membrane allows a variety of chemicals (nutrients) to flow through it. These nutrients are required for the cell’s functions to perform.  A cell’s entire surface area is just enough to hold its internal contents. Any increase in surface area might cause a massive rise in cell volume, which throws the balance off.  As a result, the ratio of surface area to interior volume determines the specific form and size of a cell. 06-09-2024 Cell Biology : Basics 27  1.4. Diversity in Cell Size and Shape: Influencing Factors 2. Nucleo-Cytoplasmic Ratio  The coordinated activity of the cell’s many components allows it to operate. The coordination between the nucleus and the cytoplasm is the most crucial.  The nucleus generates chemicals that enter the cytoplasm and regulate its activities. A cell’s cytoplasmic region is just large enough for a nucleus to regulate.  The nucleus will be unable to control its activity if the cytoplasmic region becomes too large.  As a result, a cell’s nucleo-cytoplasmic ratio never exceeds one-seventh to one-twelfth of its total size.  In certain circumstances, the presence of many nuclei in a big cell overcomes this issue. 06-09-2024 Cell Biology : Basics 28  1.4. Diversity in Cell Size and Shape: Influencing Factors 3. Rate of Cellular Activity  Despite the fact that all cells in a live organism are vital, some are metabolically more active than others.  The more active cells are generally smaller, with a higher surface-volume ratio and nucleo-cytoplasmic ratio than the bigger cells, allowing them to function more actively. 4. Cell Association  In multicellular forms that exhibit some rigidity, cell-to-cell attachment is critical.  The degree of attachment has a significant impact on the structure of the cell and its functional properties. All four variables are clearly connected, with the surface-volume ratio and nucleo-cytoplasmic ratio playing the most significant roles in determining the cell’s size, shape, and characteristics. 06-09-2024 Cell Biology : Basics 29  1.4. Types of Cells based on Morphology Cells are generally three types: 1. Prokaryotic cells: Relative simple cells with no membrane bound organelles like Golgi complex, Mitochondria, Chloroplast or Lysosomes. The hereditary material is highly coiled circular chromosome lying naked in the cytoplasm. Example: Bacterial cells 2. Eukaryotic cells: These cells contain a true nucleus. Hereditary material that is DNA is associated with basic proteins inside nucleus separated from cytoplasm by nuclear envelop. Membrane bound organelles are present like plant and animal cells. 3. Mesokaryotic cells: 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. Example: Dinoflagellates, Marine algae 06-09-2024 Cell Biology : Basics 30 1.4. Structure of Eukaryote and Prokaryote Cells Dougherty (1957) has divided cells into two types – prokaryotic cells and eukaryotic cells 06-09-2024 Cell Biology : Basics 31  Criteria Prokaryotes Eukaryotes Differences Between Eukaryotic and Type of Cell Always unicellular Unicellular and multicellular Cell Size Ranges in size from 0.1 μm – 5.0 μm in Size ranges from 10 μm – 100 μm in diameter diameter Cell Wall Usually present, chemically complex in nature When present chemically simple Prokaryotic Cells Nucleus Absent, Instead have a nucleoid region in the Present cell Ribosomes Present; Smaller in size and circular in shape Present; Comparatively larger in size and linear in shape DNA arrangement Circular in nature Linear in nature Membrane bound Absent Present organelles Plasmids Present Rarely found in eukaryotes Lysosome Absent Present Cell division/Reproduction Binary fission/Asexual Sexual and asexual Examples Archaea and Bacteria Plant and Animal Cells 06-09-2024 Cell Biology : Basics 32  1.4. Essential Features of Mesokaryotic Cells  The cells are medium-sized and the size of the cell is in between prokaryotic cells and eukaryotic cells.  They do not have a cell wall but instead have a pellicle or theca.  The cell membrane is present.  The nucleus is well-organized and surrounded by the membrane.  Membrane-bound cell organelles (like mitochondria, plastids, endoplasmic reticulum) are present in the cytoplasm.  The ribosomes in the cytoplasm are 80s type.  The histone protein is completely absent in the cell.  The chromosome is present and is formed with the help of acidic proteins.  Cell division occurs through the method of amitosis.  Flagella are present and consist of filaments. Dodge has first used the  The presence of chloroplast in the cell contains photosynthetic pigments. term mesokaryotic in 1966  Respiratory enzymes are present in the cytoplasm or mitochondria. 06-09-2024 Cell Biology : Basics 33