Cell Biology UG 1 (Unit 1) PDF

UNIT 1 c e l l  08/01/2024 Monday 1 What is a cell? 2 Who coined the word “cell”? LET US REVISE..!!! 3 Wh...

UNIT 1 c e l l  08/01/2024 Monday 1 What is a cell? 2 Who coined the word “cell”? LET US REVISE..!!! 3 Who developed the modern cell theory? 4 What did Virchow conclude that added to the cell theory?  CELL THEORY MATHIAS ROBERT ANTON VAN JACOB RUDOLF LOUIS SCHLEIDEN HOOKE LEEUWENHOEK and THEODOR VIRCHOW PASTEUR SCHWANN 1665 1675 1838-1839 1858 1865 Credited with improving Schleiden said that Concluded that gave the coining the microscope cells were the units cells arise from experimental term “cell” of structure in plants pre-existing evidence to first to (Latin word “cella”- and his coworker cells support hollow space) observe Schwann applied his also concluded Virchow’s observed a free-living theory on animals. the significance extension of cell piece of cork cells Both postulated that of cell division theory under “CELL IS THE BASIC in organisms compound UNIT OF STRUCTURE microscope AND FUNCTIONS IN ALL LIFE”  MODERN CELL THEORY All living organisms(animals, plants and microbes) are made up of one or more cells and cell products. All metabolic reactions in unicellular and multicellular organisms take place in cells. Cell originate only from other cells i.e., no cell can originate spontaneously, but comes into being only by division and duplicatiob of already existing cells. The smallest and clearly defined unit of life is the cell.  DEFINITIONS OF CELL GIVEN BY VARIOUS CELL BIOLOGISTS A.G. LOWEY and P. SIEKEVITZ(1963) defined cell as “ a unit of biological activity delimited by a semipermeable membrane and capable of self-reproduction in a medium free of other living systems” WILSON and MORRISON(1966) defined as “an integrated and continuously changing system” JOHN PAUL(1970) said cell is “the simplest integrated organization in living systems, capable of independent survival” 1.2 Prokaryotic and Eukaryotic cells PROKARYOTIC CELL It is the simplest, and therefore smaller, than a eukaryotic cell, lacking a nucleus THEY HAVE THREE and most other eukaryote organelles. ARCHITECTUAL REGIONS: There are two kinds of prokaryotes: 1) Flagella BACTERIA AND ARCHAEA. 2) Outer covering PROKARYOTIC (Gr. pro = primitive or 3) Cytoplasmic region before; karyon = nucleus) They are probabaly the first to come into existence perhaps 3.5 billion years ago. 1.2 Prokaryotic and Eukaryotic cells The prokaryotic cell consists of central nuclear components (viz., DNA molecule, RNA molecule and nuclear proteins) surrounded by cytoplasmic ground substance, with the whole enveloped by a plasma membrane or cell membrane. Neither the nucleus nor the respiratory enzyme system are separately enclosed by membranes, although the inner surface of the plasma membrane itself may serve for enzyme attachment. The cytoplasm of prokaryotic cells lacks well-defined cytoplasmic organelles such as endoplasmic reticulum, Golgi apparatus, mitochondria, centrioles, etc. They lack of nuclear envelope, and any other cytoplasmic membrane. They do not contain nucleoli, cytoskeleton (microfilament and microtubules), centrioles, etc.  09/01/2024 Prokaryotic cells - TO BE Tuesday CONTINUED CELL CYTOPLASMIC FLAGELLA ENVELOPE REGION Not present in consist of cell The cell wall The barrier also all prokaryotes wall covering the contains cell genome (DNA) consists of prevents the they facilitate plasma and ribosome and various peptidoglycan cell from movement and membrane sorts of inclusions. in bacteria, and expanding and communication though some prokaryotes can carry acts as an finally bursting between cells bacteria also additional from osmotic extrachromosomal DNA and they are have a further barrier against pressure elements called plasmids, made of covering layer exterior forces against which are usally circular. proteins called a capsule, hypotonic Plasmids enable additional This envelope environment. functions, such as antibiotic gives rigidity to cell resistance  EUKARYOTIC CELL The eukaryotic cells (Gr., eu = good, karyotic = nucleated) are essentially two enveloped systems and they are very much larger than prokaryotic cells. the major difference between prokaryotes and eukaryotes is that eukaryotes’ cells contain membrane- bound compartments in which specific metabolic activities take place. Most important among these is a cell nucleus, a membrane-delinated compartment that houses the eukaryotic cell’s DNA. This nucleus gives the eukaryote its name, which means “true nucleus”.  EUKARYOTIC CELL The eukaryotic cells are the true cells which occur in plants ( from algae to angiosperms) and animals (from Protozoa to mammals). The eukaryotic cells have various features that differentiate them from other eukaryotic cells: 1)CELL SHAPE 2)CELL SIZE 3)CELL VOLUME 4)CELL NUMBER 5) STRUCTURE  1) CELLS SHAPE SPERICAL: eggs of many FLATTENED: squamous animals epithelium CUBOIDAL: thyroid gland SPINDEL: smooth muscle follicles fibres BRANCHED: pigment cell ELONGATED: neurons of skin 2) CELL SIZE 2) CELL SIZE THINK.... THINK..... THINK...... ARE THE CELLS OF AN ELEPHANT LARGER THAN AN ANT.... 3) CELL VOLUME The volume of a cell is fairly constant for a particular cell type and is independent of the size of the organism. The kidney or liver cells are about the same size in bulls, horses and mice. The difference in the total mass of the organ or organism depends on the number, not on the volume of the cells.. BIGGER THE ANIMAL= MORE THE NUMBER OF CELL PRESENT IN THE BODY 4) CELL NUMBER The number of cells present in an organism varies from a single cell in a unicellular organism(protists such as protozoa and protophyta) to many cells in multicellular organisms (most plants, fungi and animals) The number of cells in most multicellular organisms is indefinite, but the number of cells may be fixed in some multicellular prganism  5) Structure The eukaryotic cells consists of the following components: A) CELL WALL AND PLASMA MEMBRANE B) CYTOPLASM C) NUCLEUS  15/01/2024 MONDAY DIFFFERENCE BETWEEN (with diagrams) 1)PROKARYOTIC AND EUKARYOTIC CELLS 2) PLANT CELL AND ANIMAL CELL 1.3 CELL WALL AND PLASMA MEMBRANE 16/01/2024 All cells, whether TUESDAY PROKARYOTIC OR 1) CELL WALL : The outermost structure EUKARUOTIC, have a of most plant cell is a dead and rigid layer membrane that envelopes the cell, separates its interior from called cell wall. its environment, regulates what moves in and out 2) PLASMA MEMBRANE : Every kind of (selectively permeable), and animal cell is bounded by a living, maintains the cell's electric extremely thin and delicate membrane potential. called plasmalemma, cell membrane or plasma membrane. 1.3 CELL WALL COMPOSED OF : Carbohydrates such as cellulose, pectin, hemicellulose and lignin and certain fatty acids such as waxes. Ultrastructurally cell wall is found to consist of a microfibrillar network lying in the gel-like matrix. The microfibibrils are mostly made up of cellulose. THERE IS A PECTIN-RICH cementing substance between the walls of the adjacent cells which is called MIDDLE LAMELLA. Various functions include: (1) providing the living cell with mechanical protection and a chemically buffer environment, (2) providing a porous medium for the circulation and distribution of water, minerals, and other small nutrient molecules, (3)providing rigid building blocks from which stable structures of higher order, such as leaves and stems, can be produced, and (4) providing a storage site of regulatory molecules that sense the presence of pathogenic microbes and control the development of tissues. All cell walls contain two layers, the middle lamella and the primary cell wall, and many cells produce an additional layer, called the secondary wall. The middle lamella serves as a cementing layer between the primary walls of adjacent cells. The primary wall is the cellulose-containing layer laid down by cells that are dividing and growing. To allow for cell wall expansion during growth, primary walls are thinner and less rigid than those of cells that have stopped growing.  A fully grown plant cell may retain its primary cell wall (sometimes thickening it), or it may deposit an additional, rigidifying layer of different composition, which is the secondary cell wall. Secondary cell wallsare responsible for most of the plant’s mechanical support as well as the mechanical properties prized in wood. Components of cell wall: Although primary and secondary wall layers differ in detailed chemical composition and structural organization, their basic architecture is the same, consisting of cellulose fibres of great tensile strength embedded in a water-saturated matrix of polysaccharides and structural glycoproteins.  PLASMA MEMBRANE The plasma membrane acts as a thin barrier which separates the inter-cellular fluid or the cytoplasm from the extra-cellular fluid in which the cell lives. In case of unicellular organisms (PROTOPHYTA AND PROTOZOA) the extra-cellular fluid may be fresh or marine water, while the multicellular organsims that extra-cellular fluid may be blood, lymph or interstitial fluid. 1. Plasma membrane is also referred to as the cell membrane. 2. It is the membrane found in all cells, that separates the inner part of the cell from the exterior. 3. Plasma membrane is composed of a phospholipid bilayer implanted with proteins and it is semi-permeable. 4. It is responsible to regulate the transportation of materials and the movement of substances in and out of the cell.  PLASMA MEMBRANE Function of plasma membrane: 1. The main function of the plasma membrane is that it acts as a physical barrier between the external environment and the inner cell organelles. 2. The plasma membrane is a selectively permeable membrane, which permits the movement of only certain molecules both in and out of the cell. 3. The plasma membranes also play an important role in both the endocytosis and exocytosis processes. 4. The plasma membrane also functions by facilitating communication and signaling between the cells. 5. The plasma membrane plays a vital role in anchoring the cytoskeleton to provide shape to the cell and also maintain the cell potential.  PLASMA MEMBRANE Structure of Plasma Membrane A plasma membrane is mainly composed of carbohydrates, phospholipids, proteins, and conjugated molecules, and it is about 5 to 8 nm in thickness. The plasma membrane is a flexible, lipid bilayer that surrounds and contains the cytoplasm of the cell. Based on their arrangement of molecules and the presence of certain specialized components, it is also described as the fluid mosaic model. The fluid mosaic model was first proposed in the year 1972 by American biologists Garth L. Nicolson and Seymour Jonathan Singer. The fluid mosaic model describes in detail, the plasma membrane structure in the eukaryotic cells, and how well it is arranged along with their components – phospholipids, proteins, carbohydrates and cholesterol. These components give a fluid appearance to the plasma membrane. 1.4 CELL ORGANELLES : STRUCTURE AND FUNCTIONS The cellular components are called cell organelles. These cell organelles include both membrane and non-membrane bound organelles, present within the cells and are distinct in their structures and functions. They coordinate and function efficiently for the normal functioning of the cell. A few of them function by providing shape and support, whereas some are involved in the locomotion and reproduction of a cell. Various organelles are present within the cell and classified into three categories based on the presence or absence of membrane. 1.4 CELL ORGANELLES : STRUCTURE AND FUNCTIONS Organelles without membrane: The Cell wall, Ribosomes, and Cytoskeleton are non-membrane-bound cell organelles. They are present both in the prokaryotic cell and the eukaryotic cell. Single membrane-bound organelles: Vacuole, Lysosome, Golgi Apparatus, Endoplasmic Reticulum are single membrane-bound organelles present only in a eukaryotic cell. Double membrane-bound organelles: Nucleus, mitochondria and chloroplast are double membrane-bound organelles present only in a eukaryotic cell.  1.PLASMA MEMBRANE/CELL MEMBRANE AS DISCUSSED AHEAD...... 2. CYTOPLASM The cytoplasm is present both in plant and animal cells. They are jelly-like substances, found between the cell membrane and nucleus. They are mainly composed of water, organic and inorganic compounds. The cytoplasm is one of the essential components of the cell, where all the cell organelles are embedded. These cell organelles contain enzymes, mainly responsible for controlling all metabolic activity within the cell and are the site for most of the chemical reactions within a cell.  3. NUCLEUS The nucleus is a double-membraned organelle found in all eukaryotic cells. It is the largest organelle, which functions as the control centre of the cellular activities and is the storehouse of the cell’s DNA. A nucleus, as related to genomics, is the membrane-enclosed organelle within a cell that contains the chromosomes. An array of holes, or pores, in the nuclear membrane allows for the selective passage of certain molecules (such as proteins and nucleic acids) into and out of the nucleus.  3. NUCLEUS STRUCTURE : The nucleus is dark, round, surrounded by a nuclear membrane. It is a porous membrane (like cell membrane) and forms a wall between cytoplasm and nucleus. Within the nucleus, there are tiny spherical bodies called nucleolus. It also carries an essential structure called chromosomes. FUNCTION: The nucleus controls the Chromosomes are thin and thread-like structures characters and functions of cells in our body. which carry another important structure called a The primary function of the nucleus is to gene. Genes are a hereditary unit in organisms i.e., monitor cellular activities including it helps in the inheritance of traits from one metabolism and growth by making use of generation (parents) to another (offspring). DNA’s genetic information. Nucleoli in the nucleus are responsible for the synthesis of protein and RNA.  4. ENDOPLASMIC RETICULUM The Endoplasmic Reticulum is a network of membranous canals filled with fluid. They are the transport system of the cell, involved in transporting materials throughout the cell. There are two different types of Endoplasmic Reticulum: Rough Endoplasmic Reticulum – They are composed of cisternae, tubules, and vesicles, which are found throughout the cell and are involved in protein manufacture. Smooth Endoplasmic Reticulum – They are the storage organelle, associated with the production of lipids, steroids, and also responsible for detoxifying the cell.  5. MITOCHONDRION Mitochondria are called the powerhouses of the cell as they produce energy-rich molecules for the cell. The mitochondrial genome is inherited maternally in several organisms. It is a double membrane-bound, sausage-shaped organelle, found in almost all eukaryotic cells. The term ‘mitochondrion’ is derived from the Greek words “mitos” and “chondrion” which means “thread” and “granules-like”, respectively. It was first described by a German pathologist named Richard Altmann in the year 1890.  5. MITOCHONDRION STRUCTURE : The double membranes divide its lumen into two distinct aqueous compartments. The inner compartment is called a ‘matrix’ which is folded into cristae whereas the outer membrane forms a continuous boundary with the cytoplasm. They usually vary in their size and are found either round or oval in shape. FUNCTION: Mitochondria are the sites of aerobic respiration in the cell, produce energy in the form of ATP and help in the transformation of the molecules For instance, glucose is converted into adenosine triphosphate – ATP. Mitochondria have their circular DNA, RNA molecules, ribosomes (the 70s), and a few other molecules that help in protein synthesis.  6. PLASTIDS Plastids are double-membrane organelles which are found in the cells of plants and algae. Plastids are responsible for manufacturing and storing of food. These often contain pigments that are used in photosynthesis and different types of pigments that can change the colour of the cell. Types of Plastids There are different types of plastids with their specialized functions. Among them, a few are mainly classified based on the presence or absence of the Biological pigments and their stages of development. Chloroplasts Chromoplasts Leucoplasts  6. PLASTIDS Chloroplasts – Chloroplasts are double membrane-bound organelles, which usually vary in their shape – from a disc shape to spherical, discoid, oval and ribbon. The inner membrane encloses a space called the stroma. Flattened disc-like chlorophyll- containing structures known as thylakoids are arranged in a stacked manner like a pile of coins. Each pile is called a granum (plural: grana) and the thylakoids of different grana are connected by flat membranous tubules known as stromal lamella. Just like the mitochondrial matrix, the stroma of chloroplast also contains a double-stranded circular DNA, 70S ribosomes, and enzymes which are required for the synthesis of carbohydrates and proteins. Chromoplasts – The chromoplasts include fat-soluble, carotenoid pigments like xanthophylls, carotene, etc. which provide the plants with their characteristic color – yellow, orange, red, etc. Leucoplasts – Leucoplasts are colorless plastids which store nutrients. Amyloplasts store carbohydrates (like starch in potatoes), aleuroplasts store proteins, and elaioplasts store oils and fats.  7. GOLGI APPARATUS Golgi Apparatus is also termed as Golgi Complex. It is a membrane-bound organelle, which is mainly composed of a series of flattened, stacked pouches called cisternae. This cell organelle is primarily responsible for transporting, modifying, and packaging proteins and lipids to targeted destinations. Golgi Apparatus is found within the cytoplasm of a cell and is present in both plant and animal cells.  8. MICROBODIES Microbodies are membrane-bound, minute, vesicular organelles, found in both plant and animal cells. They contain various enzymes and proteins and can be visualized only under the electron microscope.  9. CYTOSKELETON It is a continuous network of filamentous proteinaceous structures that run throughout the cytoplasm, from the nucleus to the plasma membrane. It is found in all living cells, notably in the eukaryotes. The cytoskeleton matrix is composed of different types of proteins that can divide rapidly or disassemble depending on the requirement of the cells. The primary functions include providing the shape and mechanical resistance to the cell against deformation, the contractile nature of the filaments helps in motility during cytokinesis.  10. CILIA AND FLAGELLUM Cilia are hair-like projections, small structures, present outside the cell wall and work like oars to either move the cell or the extracellular fluid. Flagella are slightly bigger and are responsible for the cell movements. The core of the cilium and flagellum is called an axoneme, which contains nine pairs of gradually arranged peripheral microtubules and a set of central microtubules running parallel to the axis. The central tubules are interconnected by a bridge and are embedded by a central sheath. One of the peripheral microtubular pairs is also interconnected to the central sheath by a radial spoke. Hence there are a total of 9 radial spokes. The cilia and flagella emerge from centriole-like structures called basal bodies.  10.CENTROSOME AND CENTRIOLE The centrosome organelle is made up of two mutually perpendicular structures known as centrioles. Each centriole is composed of 9 equally spaced peripheral fibrils of tubulin protein, and the fibril is a set of interlinked triplets. The core part of the centriole is known as a hub and is proteinaceous. The hub connects the peripheral fibrils via radial spoke, which is made up of proteins. The centrioles from the basal bodies of the cilia and flagella give rise to spindle fibres during cell division.  11. VACUOLE Vacuoles are mostly defined as storage bubbles of irregular shapes which are found in cells. They are fluid-filled organelles enclosed by a membrane. The vacuole stores the food or a variety of nutrients that a cell might need to survive. In addition to this, it also stores waste products. The waste products are eventually thrown out by vacuoles. Thus, the rest of the cell is protected from contamination. The animal and plant cells have different size and number of vacuoles. Compared to the animals, plant cells have larger vacuoles.