Cell: The Unit of Life - PDF

Welcome to Cell: The Unit of Life © 2022, Aakash BYJU'S. All rights reserved Key Takeaways Cell Cell theory Classification of cell Prokaryotic cell Characteristics features Cell envelope Cytoplasm © 2022, Aakash BYJU'S. All rights reserved Eukaryotic Cell Characteristics features Cell Wall Cell memb...

Welcome to Cell: The Unit of Life © 2022, Aakash BYJU'S. All rights reserved Key Takeaways Cell Cell theory Classification of cell Prokaryotic cell Characteristics features Cell envelope Cytoplasm © 2022, Aakash BYJU'S. All rights reserved Eukaryotic Cell Characteristics features Cell Wall Cell membrane Cytoplasm Endomembrane system Mitochondria Plastids Ribosomes Cytoskeleton Cilia and Flagella Centrosome and centrioles Nucleus Microbodies Summary © 2022, Aakash BYJU'S. All rights reserved Cell Cell is the fundamental, structural, and functional unit of life. Cell is capable of  independent existence  performing essential functions of life © 2022, Aakash BYJU'S. All rights reserved Cell Theory Robert Brown Robert Hooke Observed that all plants are composed of different kinds of cells which form tissues First to observe live cells (animal cells) 1665 1674 Observed dead cork cells Theodore Schwann 1831 1838 Discovered the nucleus Coined the term ‘cell’ Anton Van Leeuwenhoek © 2022, Aakash BYJU'S. All rights reserved Matthias Schleiden First to explain that cells are formed from preexisting cells (Omnis cellula-e cellula) 1839 Noticed that cells have a thin outer layer (plasma membrane) Concluded that plants have a cell wall Hypothesized, bodies of animals and plants are composed of cells 1855 Rudolf Virchow Cell Theory Matthias Schleiden and Theodore Schwann identified key differences between the two cell types and put forth the idea that cells were the fundamental units of both plants and animals. MATTHIAS SCHLEIDEN (1838) Observed that all plants are made up of different types of cells © 2022, Aakash BYJU'S. All rights reserved CELL THEORY All plants and animals are composed of cells and cell products THEODORE SCHWANN (1839) Observed that all animals are made up of different types of cells Cell Theory Rudolf Virchow modified the hypothesis of Schleiden and Schwann to give the cell theory a final shape. Rudolf Virchow first explained that cells divide, and new cells are formed from the preexisting cells (Omnis cellula-e cellula). MODERN CELL THEORY CELL THEORY All plants and animals are composed of cells and cell products © 2022, Aakash BYJU'S. All rights reserved All organisms are composed of cells and cell products All cells arise from pre-existing cells RUDOLF VIRCHOW (1855) Omnis cellula e cellula Cell Theory 01 3 Principles of cell theory All living organisms are composed of cells and products of cells 02 All cells arise from pre-existing cells 03 Activities of an organism are the outcome of sum total of activities and interactions of its constituent cells Exception to cell theory: Viruses are not made up of cells. They are composed of nucleoprotein particles. Therefore, they are not considered either living or non-living. © 2022, Aakash BYJU'S. All rights reserved Did You Know? The smallest cell Mycoplasma 0.3 µm in length © 2022, Aakash BYJU'S. All rights reserved The largest cell Ostrich egg Largest isolated single cell The longest cell Nerve cell of giant squid Classification of Cell Based on shape: Based on size: RBCs Skin cells Disc shaped Polygonal © 2022, Aakash BYJU'S. All rights reserved Thread-like Salivary ducts lining Cuboidal Amoeba WBCs Mesophylls Tracheids Irregular Amoeboid Round and oval Elongated 0.02 to 0.2 μm Virus Large intestine cells Columnar Neuron Mycoplasma Bacterium 0.3 or 0.1 μm 1 to 2 μm Prokaryotic cell Animal cell Plant cell 10 to 20 μm Eukaryotic cell Classification of Organisms Unicellular organism: Based on number: Made up of a single cell Functional unit which is capable of respiration, excretion, etc. and capable of independent existence Bacteria Amoeba Yeast Multicellular organism: Made up of more than one cell Specialised cells perform different functions Cells then interact with one another to maintain life Plants Animals Prokaryotic organism: Based on the organisation of genetic material: Cells without a well-defined nucleus Genetic material is not enclosed in well-defined membrane-bound structure Prokaryotic organism Eukaryotic organism: Cells with a true nucleus Genetic material is bound by well-defined structure Eukaryotic organism © 2022, Aakash BYJU'S. All rights reserved Prokaryotic Cells Characteristic features : Lack membrane-bound organelles such as endoplasmic reticulum (ER), Golgi complex, lysosomes, mitochondria, microbodies and vacuoles. Exception: Ribosomes (non-membrane bound) Cell wall Pilus Capsule Represented by bacteria, Pleuropneumonia like Plasma membrane Organisms (PPLO), blue green algae, mycoplasma Generally smaller in size and multiply more rapidly than eukaryotic cells Cell wall surrounds cell membrane (except Mycoplasma) Cytoplasm Plasmid No well-defined nucleus, as it is not enveloped by a membrane. Genetic material is naked Fluid matrix filling the cell is cytoplasm Many bacteria have smaller circular DNA outside genomic DNA called plasmids. Unique characteristics - antibiotic resistance to bacteria © 2022, Aakash BYJU'S. All rights reserved Nucleoid (DNA) Ribosomes Flagella Cell Envelope Cell envelope consists of complex, three-layered structure Glycocalyx (outer) Cell wall (middle) Cell membrane (inner) Cell wall Cell membrane Glycocalyx Each perform different functions but act together as a single protective unit. © 2022, Aakash BYJU'S. All rights reserved Cell Envelope 1. Glycocalyx : Outermost layer of cell envelope Has a coating of mucous or polysaccharides macromolecules, which protects the cells and helps in adhesion Composition - (Carbohydrate + proteins) and thickness vary among different bacteria Glycocalyx Glycocalyx Slime layer Capsule Loose sheath Thick and tough layer Protects from loss of water Provides gummy and sticky character to the cell Allows bacterium to hide from host's immune system © 2022, Aakash BYJU'S. All rights reserved Cell Envelope 2. Cell wall : Middle layer of the cell envelope Provides shape and strong structural support to the bacteria from bursting or collapsing Rigid due to a special macromolecule called peptidoglycan (murein or mucopeptide), polymer of N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) Number of antibiotics (e.g., penicillin) inhibits cross-linking of peptidoglycan strands. Therefore, cells undergo lysis in the presence of these antibiotics Gram staining is a special technique, which classified bacteria into two groups, viz. Gram-positive and Gramnegative bacteria. © 2022, Aakash BYJU'S. All rights reserved Cell wall Cell Envelope 2. Cell wall : Hans Christian devised a method to distinguish bacteria based on the differences they exhibit in their cell wall composition Method is called Gram staining, also known as Gram's method Application of gram staining: ○ Heat fixation of bacterial smear on the slide to affix the bacteria to the slide to avoid rinsing out during the staining procedure ○ Applying a primary stain (crystal violet) ○ Addition of KI solution, which binds to crystal violet and traps it in the cell ○ After staining, slide is washed with acetone or ethyl alcohol (Rapid decolorization) ○ Counterstaining with safranin © 2022, Aakash BYJU'S. All rights reserved Cell Envelope 2. Cell wall : Gram-positive bacteria have a thicker cell wall made of peptidoglycan and are stained purple by crystal violet. Gram-negative bacteria have a thinner layer so do not retain the purple stain and are counter-stained pink by safranin. Crystal violet All purple Iodine All purple © 2022, Aakash BYJU'S. All rights reserved Alcohol (Decolourize) G +ve = Purple G -ve = Colorless Safranin G +ve = Purple G -ve = Pink Gram Positive Gram Negative Cell Envelope 2. Gram staining Cell wall : Gram negative Gram positive Cell wall is single layered and smooth Cell wall is double layered and wavy Have larger/ thick amount of peptidoglycan in their cell wall Have lesser/ thin amount of peptidoglycan in their cell wall Take up the gram stain Do not take up the gram stain Lipopolysaccharides Peptidoglycan layers Peptidoglycan Cell membrane © 2022, Aakash BYJU'S. All rights reserved Outer membrane Cell Envelope 2. Cell wall : Extensions Flagella: Thin filamentous extensions Play significant role in motility The flagellum is composed of three parts - filaments, hook and basal body. The filament is the longest portion and extends from the cell surface to the outside. Filament It is a hollow rigid cylindrical structure made up of the protein called flagellin. Basal body is a rod-like structure which consists of rings. Organisms Motile (flagella present) © 2022, Aakash BYJU'S. All rights reserved Non-motile (flagella absent) Basal body Hook Cell wall Cell membrane Cell Envelope 3. Cell membrane / plasma membrane: Innermost layer of cell envelope Selectively permeable in nature and interacts with the outside world It is similar structurally to that of the eukaryotes Composition: Phospholipid bilayer, membrane proteins and carbohydrates Phospholipid bilayer Carbohydrate © 2022, Aakash BYJU'S. All rights reserved Cell membrane Peripheral protein Integral protein Cell Envelope 3. Cell membrane / plasma membrane: Extensions Mesosomes: Special membranous structure which are extensions of plasma membrane into the cell, in the form of vesicles, tubules and lamellae Functions - cell wall formation, DNA replication and distribution to daughter cells. Also help in respiration, secretion process, to increase the surface area of the plasma membrane and enzymatic content Cell wall Plasma membrane Mesosome Found in gram positive bacteria Chromatophores: Membranous extensions into the cytoplasm, which contain pigments Found in photosynthetic prokaryotes like cyanobacteria (Nostoc), and purple bacteria © 2022, Aakash BYJU'S. All rights reserved Cell Envelope 3. Cell membrane / plasma membrane: Extensions Pilli: Do not play a role in motility Elongated tubular structures, made up of a special protein i.e., pilin True pili are found only in Gram-negative bacteria so far and in these forms they are involved in mating process, (conjugation) Fimbriae: Do not play a role in motility Small bristle-like fibres sprouting out of the cell In some bacteria, they are known to help in attaching the bacteria to rocks in streams and also to the host tissues. © 2022, Aakash BYJU'S. All rights reserved Cytoplasm Jelly-like, semi-fluid matrix inside the cell, where various biochemical reactions occurs Consists of enzymes, nutrients, gases, plasmid and nucleoid, storage bodies and other cell structures Membrane-bound organelles like mitochondria, Golgi bodies, chloroplast, and lysosomes are absent. Organelles without membranes are present, such as, Ribosomes (70S type) and inclusion bodies 1. Ribosomes Ribosomes, a non-membrane bound organelles size is 15 nm by 20 nm, associated with the plasma membrane of the cell Made up of RNA and proteins Consists of two subunits - 50 S (large) and 30 S (small) units which when present together form 70 S ribosomes Site of protein synthesis Cytoplasmic ribosomes synthesise proteins, which remain within the cells Ribosomes on the plasma membrane make proteins that are transported out Several ribosomes may attach to a single mRNA and form a chain called polysome or polyribosomes. The ribosomes of a polysome translate the mRNA into proteins. © 2022, Aakash BYJU'S. All rights reserved 50S 30S Polysome 70S Ribosome Cytoplasm 2. Inclusion bodies Lie freely in cytoplasm, non-membrane bound and store reserve material Single layer, non-unit membrane, which is 2-4 nm thick 3. E.g., phosphate granules, cyanophycean granules and glycogen granules E.g., poly-ß-hydroxybutyrate granules, sulphur granules and gas vacuole Gas vacuoles : Found in blue-green algae, purple and green photosynthetic bacteria Nucleoid No well-defined nucleus Presence of nucleoid: Dense area in the cell that contains the genetic material Nucleoid © 2022, Aakash BYJU'S. All rights reserved Eukaryotic Cells Characteristic features : Presence of true nucleus enclosed by a nuclear envelope Presence of membrane bound organelles Genetic material is organised into chromosomes Has a variety of complex locomotory and cytoskeletal structures These cells occur in protists, fungi, plants and animals Nucleus Ribosomes SER RER Plasma membrane Lysosome Centrioles Peroxisome Golgi apparatus Cytoskeleton Mitochondria Animal cell © 2022, Aakash BYJU'S. All rights reserved Nucleus Cytosol Vacuole Cell wall Nucleus Endoplasmic Reticulum Cell membrane Ribosomes Golgi apparatus Chloroplast Mitochondria Plant cell Cell Wall Characteristic features : An additional non-living, rigid structure which surrounds the plasma membrane of bacteria, fungi, algae and plant cells Absent in animal cells The composition of cell wall varies in different groups Fungal cell wall Chitin, a polymer of N-acetylglucosamine (NAG) units Fungi Algal cell wall Algae Galactans, mannans and minerals like calcium carbonate Plant cell wall Insoluble polysaccharides (cellulose) hemicellulose, pectins, proteins © 2022, Aakash BYJU'S. All rights reserved Plant Cell Wall Characteristic features : The cell wall of plants consists of two regions : primary wall and secondary wall. Primary wall: It is found in young plant cells. It is a thin single layer which is elastic in nature and capable of expanding in a growing cell such as, meristematic and parenchymatous cells. Secondary wall : It is found in mature cells. It has more layers than primary wall, which brings about thickening of the cell wall such as, lignified and suberised cell wall. © 2022, Aakash BYJU'S. All rights reserved Primary cell wall S1 S2 Plant cell Plant cell S3 Secondary cell wall layers Cell Wall Characteristic features : Middle lamella : Hold adjacent cells together by a thin, sticky, amorphous layer of cementing material Middle lamella Made up of calcium and magnesium pectate Plant cell Plant cell Plant cell Plant cell Plasmodesmata : Intercellular cytoplasmic connections Endoplasmic reticulum plays a role in origin of plasmodesmata Functions : Plasmodesmata It maintains shape of the cells. It protects the cell from mechanical injury. It wards off the attacks of pathogens like viruses, bacteria, fungi, etc. It allows the materials to pass in and out of the cell. It helps in cell-to-cell interaction and provides barrier to undesirable macromolecules. © 2022, Aakash BYJU'S. All rights reserved Cell Wall Middle lamella (white) Primary wall (blue) Secondary wall (olive) Pits : At certain places secondary wall is not laid down. Such unthickened areas are called pits Adjacent cells are generally opposite to each other and form pit pairs Pit Pits are of two types : o Simple pit : Uniform pit cavity in diameter o Bordered pit: Flask-shaped pit cavity as in tracheid Torus Presence of number of plasmodesmata or cytoplasmic strands are in pit through which the cytoplasm of one cell is in contact with other o Lined by plasma membrane and contains a fine tubule called desmotubule Bordered pits Simple pits Pits © 2022, Aakash BYJU'S. All rights reserved Cell Membrane Characteristics features : Cell membrane or plasma membrane is selectively permeable. Composition: phospholipids, membrane proteins, carbohydrate groups (glycolipids and glycoproteins) The ratio of protein and lipid varies considerably in different cell types. In human beings, the membrane of the erythrocyte (RBC) has approximately 52 % protein and 40 % lipids. Bilayer lipid arrangement – Polar head (hydrophilic) towards the outer sides, interacts with the water and the non-polar (hydrophobic) tails towards the inner sides. Hence, non-polar tail of saturated hydrocarbons or hydrophobic tail is protected from the aqueous environment. Phospholipid bilayer Peripheral protein Cholesterol Lipid (Fatty acid) Hydrophilic phosphate head Hydrophobic lipid tail Carbohydrate © 2022, Aakash BYJU'S. All rights reserved Integral protein Phospholipid bilayer Cell Membrane Characteristics features : In cell membrane, two types of membrane proteins are present, depending on the ease of extraction: peripheral and integral Membrane proteins Peripheral proteins Integral proteins Lie on the membrane surface Partially or totally buried in Peripheral membrane protein Integral membrane proteins membrane Tunnel proteins, which run through the lipid bilayer are known as trans membrane proteins These proteins cannot be removed easily, and their removal requires crude methods of treatment like detergents. Thus, the membrane has been described as protein icebergs floating in sea of phospholipids. © 2022, Aakash BYJU'S. All rights reserved Cell Membrane Characteristics features : Structure: Fluid mosaic model proposed by Singer and Nicolson (1972) Fluidity: Quasi-fluid nature of lipid allows lateral movement of proteins within the bilayer Movement Flip-flop Lateral Seen in lipids and proteins Occurs within the same monolayer Seen in lipids (more common) but not in proteins due to their large size Slower than lateral movement More common Movement from one monolayer to the other Functions : Cell growth, formation of intercellular junctions, secretion, endocytosis, cell division, etc. Transport of the molecules © 2022, Aakash BYJU'S. All rights reserved Cell Membrane Membrane transport Passive transport Active transport Movement of neutral solutes along the concentration gradient (Higher to lower concentration) Movement of ions or molecules against the concentration gradient (Lower to higher concentration) By simple diffusion No energy utilised Transporters such as Na+/K+ pump in animal cells Energy dependant (ATP is utilised) © 2022, Aakash BYJU'S. All rights reserved Cytoplasm Jelly-like, semi-fluid matrix that fills the cell Main arena of cellular activities in both plants and animal cells Various biochemical reactions occur in it, to keep the cell in its living state Components Cytosol Clear fluid part of the cytoplasm Constitutes 90% of water Consists of proteins, lipids, and inorganic salts © 2022, Aakash BYJU'S. All rights reserved Organelles Scattered in the cytosol Suspended organelles are the mitochondria, endoplasmic reticulum, Golgi apparatus, vacuoles, lysosomes, chloroplasts in plant cell Cytoplasm (semi-fluid matrix of the cell) Endomembrane System Membranous cell organelles which function in a coordinated manner Involved in the packaging and transport of materials Absent in prokaryotic cells and RBCs of mammals Endomembrane system Endoplasmic reticulum © 2022, Aakash BYJU'S. All rights reserved Golgi complex Lysosomes Vacuoles Endomembrane System Endoplasmic reticulum A network of reticulum of tiny tubular structures scattered in the cytoplasm. Endomembrane system (composed of three kind of structures) Cisternae Actively involved in protein synthesis; e.g., cells of pancreas and brain. Associated with large subunit (60 S) Involved in lipid and sterol synthesis Tubules Cisternal space Cisternae © 2022, Aakash BYJU'S. All rights reserved Vesicles Tubules Abundant in the pancreatic cells and these are the only ER structures found in spermatocytes Endomembrane System Endoplasmic reticulum ER divides the intracellular space into two distinct compartments : Luminal compartment and extra luminal compartment. Intracellular space Luminal compartment Extra luminal compartment Internal space which enclosed by ER membrane. © 2022, Aakash BYJU'S. All rights reserved Space present outside the ER in the cytoplasm. Endomembrane System Endoplasmic reticulum ER are of two types on the basis of presence/ absence of ribosomes on the surface of ER. Endoplasmic reticulum Smooth endoplasmic reticulum Rough endoplasmic reticulum Absence of ribosomes Presence of ribosomes Smooth tubular structures. Eg., Muscle cells, those ER known as sarcoplasmic reticulum. Contains two types of glycoproteins i.e., Ribophorin-l and Ribophorin-Il for the attachment of 60S subunit of 80S ribosome. Ribosome © 2022, Aakash BYJU'S. All rights reserved Endomembrane System Endoplasmic reticulum Endoplasmic reticulum Smooth endoplasmic reticulum Rough endoplasmic reticulum Function : Function : Lipids and steroids synthesis Site of protein synthesis Detoxification of drugs and xenobiotics, as it is associated with cytochrome P 450 Provides precursors of enzymes for the formation of lysosomes in Golgi complex Muscle contraction by release and uptake of Ca+ ions Synthetic products of RER pass onto Golgi complex through SER © 2022, Aakash BYJU'S. All rights reserved Gives rise to SER Endomembrane System Golgi Apparatus Cisternae First observed by Camillo Golgi in 1898 Densely stained reticular structures; present near the nucleus of the cell Present in eukaryotic cells, except in mature sieve tubes of plants, mature RBCs of mammals, sperm cells of bryophytes and pteridophytes, etc Vesicle Tubules In plants, it is called dictyosomes as Golgi apparatus is made up of unconnected units Golgi apparatus Cisternae Flattened sac-like structures stacked on one another © 2022, Aakash BYJU'S. All rights reserved Tubules Small, flat, interconnecting structures Vesicles Small rounded sacs present at the edges of cisternae in clusters Golgian Vacuoles Large, spherical vacuoles produced at maturing face Endomembrane System Golgi Apparatus  Concentrically arranged near the nucleus as convex cis or the forming face and concave trans or the maturing face. Cis and trans are entirely different but interconnected. Golgi apparatus arrangement Cis face  Faces the endoplasmic reticulum Trans face Cis face Transport vesicles from ER  Convex in shape forming face receiving end  Receives vesicles from the ER © 2022, Aakash BYJU'S. All rights reserved Vesicles from trans face Trans face  Faces the cytoplasm  Concave in shape maturing face  Modified materials are packed and released from the trans face Endomembrane System Golgi Apparatus: Functions 1 To process, package and transport the materials for secretions 2 Site of formation of glycoproteins and glycolipids 3 Root cap cells are rich in Golgi bodies which secrete mucilage for the lubrication of root tip 4 Acrosome of the sperm is modified Golgi apparatus 5 Formation of plasma membrane during cytokinesis © 2022, Aakash BYJU'S. All rights reserved Endomembrane System Lysosomes HYDROLYTIC ENZYMES Simple, tiny, spherical, sac-like and single membrane bound structures Formed by the process of packaging in the Golgi apparatus 1. Protein Protease Rich in hydrolytic enzymes. 2. Lipid Lipase Optimally active at the acidic pH Acidic conditions are maintained inside the lysosomes by pumping of H+ ions into them © 2022, Aakash BYJU'S. All rights reserved Membrane Hydrolytic enzymes SUBSTANCES 3. Carbohydrates Glycosidase 4. Nucleic acids Nuclease 5. Phosphates Acid phosphatase 6. Sulphates Sulphatase Endomembrane System Lysosomes Lysosomes polymorphism Primary Newly formed Secondary / Heterolysosomes Residual Primary lysosome + Phagosome Undigested materials Autophagic/Vacuolar lysosomes  Formed by union of many primary lysosomes around old or dead organelles  Surrounds and digest them by autolysis or autodigestion The disappearance of larval organs during metamorphosis (e.g., tail in frog) is due to autolysis. Hence, lysosomes are known as “suicide bags” © 2022, Aakash BYJU'S. All rights reserved Endomembrane System Vacuoles Vacuoles are large membrane-bound space. They are prominently found in the cytoplasm. It contains water, sap, excretory products. These are also called sap vacuoles. Its membrane is called tonoplast. Tonoplast facilitates the transport of ions and other materials against concentration gradients into the vacuole. Thus, ions concentration is significantly higher in the vacuole than in the cytoplasm. In plant cells, the vacuoles can occupy upto 90 % of the volume of the cell. © 2022, Aakash BYJU'S. All rights reserved Chloroplast Golgi body Cell wall Cell membrane Cytoplasm SER Nucleus Tonoplast (membrane of vacuole) RER Vacuole Mitochondria Plant cell Endomembrane System Vacuoles Types of vacuoles Contractile vacuole In Amoeba, it helps in excretion Helps in osmoregulation © 2022, Aakash BYJU'S. All rights reserved Gas vacuole/ pseudo vacuoles Food vacuole In many cells, as in protists, food vacuoles are formed by engulfing the food particles Food particle Food vacuole Membrane less vacuoles found in prokaryotes Provides buoyancy Did You Know? Mitochondria and Chloroplast Mitochondria and chloroplast are self-duplicating/ semi- autonomous organelles o Mitochondria arise by the division of pre-existing mitochondria o Chloroplast arise from proplastids Inner membrane Cristae Matrix Outer membrane For duplication, they have circular dsDNA, 70S ribosomes and different types of RNAs i.e., mRNA, tRNA, rRNA for protein synthesis. They are also bacterial endosymbionts of cells, because Inter membrane space Mitochondria Stroma Lamella o Have own nucleic acids (circular ds DNA and RNA) and 70S ribosomes Grana Inner membrane Intermembrane space o Membrane resembles that of bacteria (have proteins called porins) o ETS and ATP forming machinery is present Lipid droplet Starch granule Ribosome Chloroplast DNA Chloroplast © 2022, Aakash BYJU'S. All rights reserved Mitochondria Sausage-shaped double membraned organelles. Since they are not visible easily, they are stained by a vital stain Janus Green. Number : Depends on the amount of work done by the cell and its energy requirement Structure : Double membrane Structure Inner membrane Outer membrane Inner membrane Number of infoldings called the cristae Has 80% protein and 20% lipids and is rich in cardiolipins Contains ATP synthase/F0-F1 © 2022, Aakash BYJU'S. All rights reserved Cristae Inter membrane space Matrix Outer membrane Smooth Chemically composed of 40% lipid and 60% proteins Contains transport proteins Mitochondria Has two distinct chambers filled with aqueous fluid Chambers Outer compartment or intermembrane space Inner compartment or matrix  It is between the two mitochondrial membranes.  It is inside the inner membrane.  It is also called perimitochondrial space.  The cristae are formed from particle infolding of inner membrane towards the matrix which increases the surface area for enzyme action. © 2022, Aakash BYJU'S. All rights reserved Mitochondria Matrix contains single circular dsDNA molecule (with high G = C content), a few RNA molecules, 70S ribosomes and enzymes for TCA (Tricarboxylic acid) cycle. Mitochondria divide by fission. The cristae and inner surface of the inner membrane are studied with numerous spherical or knob like protuberances called elementary particles or Particles of Fernandez and Moran or F, particles or oxysomes. Each oxysome is differentiated into base, stalk and headpiece. The head piece contains enzyme ATP synthetase which brings about oxidative phosphorylation coupled with release of ATP. Inner membrane Functions : Mitochondria are main sites of aerobic respiration and ATP synthesis, therefore “Powerhouse of the cell”. They bring about the oxidation of carbohydrates, proteins and ß-oxidation of fats. © 2022, Aakash BYJU'S. All rights reserved Cristae Inter membrane space Matrix Outer membrane Plastids Plastids Chloroplasts Contain various pigments like chlorophyll and carotenoids Greenish in colour Take part in the synthesis of food Leucoplasts Colourless and store nutrients Granum is absent Amyloplasts : store carbohydrates e.g., potato tuber, rice etc. Majorly found in mesophyll cells Elaioplasts : store fats and oils e.g., castor Aleuroplasts : store proteins e.g., aleurone cells of maize © 2022, Aakash BYJU'S. All rights reserved Chromoplasts Have fat soluble pigments (carotene and xanthophylls). Yellow, orange or reddish in colour Change of colour from green to reddish during the ripening of tomato and chilli is due to transformation of chloroplasts to chromoplasts Orange colour of carrot roots is due to chromoplasts Plastids Chloroplast  Shape : Spherical, lens shaped, oval, discoid or even ribbon-shaped in some plants  Structure: 1. Double membrane Outer membrane : More permeable Inner membrane : Less permeable with more carrier proteins Functions:  Photosynthesis : Light reaction (in thylakoids), dark reaction (in stroma)  Storage of starch Stroma Lamella Grana Inner membrane 2. Stroma: Fluid matrix bound by the inner membrane. Contains 70S ribosomes, circular DNA (dsDNA), starch granules and enzymes required for the synthesis of carbohydrates and proteins 3. Thylakoids: Coin like structures containing chlorophyll. Enclose a space called a lumen 4. Grana/Intergranal thylakoids: Appear like piles of coin. Stacked one over the other to form grana 5. Stroma Lamellae : Flat membranous tubules. Interconnect thylakoids of different grana © 2022, Aakash BYJU'S. All rights reserved Intermembrane space Starch granule Ribosome Lipid droplet Chloroplast DNA Ribosomes Smallest non-membranous organelle, composed of RNA and protein Discovered by George Palade in 1953 Structure: Composed of two subunits, one large dome shaped and other smaller cap shaped Both the subunits remain united with each other due to a specific concentration of the Mg2+ ions If concentration of Mg2+ ions reduces below a critical level, subunits get separated. If concentration of Mg2+ ions increases in the matrix, they unites and form dimer. During protein synthesis, many ribosomes form a chain on a common messenger RNA and form the polyribosomes or polysomes. ‘S’ (Svedberg unit) – sedimentation coefficient and Indirect measure of density and size. © 2022, Aakash BYJU'S. All rights reserved Large subunit Small subunit Ribosomes Types of ribosomes 70S Present in prokaryotic cells Subunits 30S and 50S 70 S ribosomes have ribonucleoproteins in the ratio of 60 : 40 (RNA : Protein) 70 S ribosomes consist of: 30 S smaller subunit - 21 proteins and 16 S rRNA 50 S larger subunit- 34 proteins molecules and 23 S and 5 S rRNA 80S Present in eukaryotic cells Subunits 60S and 40S 80 S ribosomes have ribonucleoproteins in the ratio of 40 : 60 (RNA : Protein) 80 S ribosomes consist of: 40 S smaller subunit - with 33 protein and a single 18S-rRNA. 60 S larger subunit - with 40 protein molecules and three types of rRNAs 28S, 5.8S and 5S. Functions : sites of protein synthesis. Free Ribosomes - synthesise non-secretory proteins (structural and enzymatic proteins) ER bound ribosomes- synthesis secretory proteins (proteins for transport) Thus, these organelles are also known as protein factories Newly synthesised proteins are processed with the help of chaperone protein © 2022, Aakash BYJU'S. All rights reserved Cytoskeleton Extremely minute, fibrous, filamentous and tubular proteinaceous structures. Main functions are, to provide mechanical support, motility, maintenance of the shape of the cell. Cytoskeleton Microtubules  Found in the cytoplasmic matrix  Occurs in cilia, flagella, centrioles and basal bodies, mitotic apparatus etc  Hollow, unbranched cylinders  Composed of 13 parallel protofilaments {alpha and beta subunits of tubulin protein (non contractile protein)}  The assembly and disassembly of microtubules require GTP and Ca2+ © 2022, Aakash BYJU'S. All rights reserved Microfilaments  Solid, unbranched, rod-like fibrils of indefinite length  Composed of a globular protein actin and filamentous protein myosin.  Forms an extensive network in the cytoplasm of cells. Intermediate filaments  Non-contractile hollow filaments of acidic proteins. Microtubules Intermediate filaments Microfilaments Cytoskeleton Functions of Cytoskeleton Microtubules Microfilaments Functions : o Formation of spindles and astral rays during cell division Functions: o Provide support to plasma membrane o Form the cytoskeleton of cilia and flagella o Involved in cytoplasmic streaming and amoeboid movements o Provide shape, rigidity, motility, and anaphasic movement of chromosomes o Intracellular transport of nutrients and inorganic ions o Position of the future cell plate is determined by microtubules © 2022, Aakash BYJU'S. All rights reserved o Formation of pseudopodia and cleavage furrow during cell division Intermediate filaments Functions: o Formation of scaffolds for chromatin and in forming a basket around nucleus Centrosome and Centrioles They consist of two cylindrical structures called centrioles. Surrounded by a cloud of amorphous pericentriolar material called centrosphere or kinoplasm Two centrioles are together referred to as diplosome Centrioles are found in almost all eukaryotic cells like animal cells, fungi and algae but not found in higher plant cells. Structure of a Centriole: o A centriole possesses a whorl of nine evenly spaced peripheral fibrils of tubulin. It is absent in the centre. Therefore, the arrangement is called 9 + 0. o Each fibril is made up of three subfibres called triplet fibril. o The adjacent triplet fibrils are connected by proteinaceous linkers. © 2022, Aakash BYJU'S. All rights reserved Centrosome Centrioles Animal cell Centrosome and Centrioles The centre of the centriole possesses a rod-shaped proteinaceous mass known as hub. From the hub, nine proteinaceous strands are developed towards the peripheral triplet fibrils. These strands are called radial spokes. Due to the presence of radial spokes and peripheral fibrils, the centriole gives a cartwheel appearance. The centrioles are surrounded by dense amorphous, protoplasmic spheres in one or more series called as massules or pericentriolar satellites. They help in the formation of new centrioles. Functions : o o Form basal bodies which give rise to cilia and flagella Form the spindle fibres that give rise to spindle apparatus during cell division © 2022, Aakash BYJU'S. All rights reserved Fibril (Triplet microtubules) Hub Spokes Cilia and Flagella  Fine hairlike outgrowths of the membrane  Flagella are found in both prokaryotic and eukaryotic cells but, are structurally different  Both are membrane-bound extensions of the plasma membrane Structure:  Made up of four parts, basal body, rootlets, basal plate and shaft.  Core of the structure is known as the axoneme Axoneme (core of the structure) (9+2 arrangement) Peripheral microtubules (9) © 2022, Aakash BYJU'S. All rights reserved Central microtubules (2) Central Sheath Linkers Cilia and Flagella Structure: Axoneme consists of nine microtubule doublets radially arranged known as, peripheral microtubules. They run parallel to the long axis around one pair of central microtubules. This is 9 + 2 pattern of microtubules. Central sheath covers the central microtubules. Linkers join the microtubule doublets, made up of Nexin protein. Dynein are proteins of the subfril arms, that use ATP to drive the movement. Dynein head Plasma membrane Radial spokes Central microtubules Linkers © 2022, Aakash BYJU'S. All rights reserved Doublets Central sheath Peripheral microtubule Cilia and Flagella Cilia Flagella Very large in number and smaller in size. 1-4 in number and longer in size. Occurs throughout or major part of surface of the cell Commonly found at the surface of a cell at the one end of the cell Help in locomotion, feeding, circulation etc Help in locomotion Oar like movements. Whip like structure © 2022, Aakash BYJU'S. All rights reserved Nucleus Described by Robert Brown as early as 1831 Types of cells (based on number of nucleus) Binucleate Two nuclei per cell, e.g., Paramecium Multinucleate Have many nuclei, e.g., Opalina. Anucleate Lack nucleus at maturity, e.g., mammalian RBCs and sieve tube cells. Store house of hereditary information Was proved by Hammering (1953) Flemming observed some intensely stained parts in nucleus and called them ‘chromatin’ Known as ‘brain’ of the cell as it controls the whole cell and its functions Contains the genetic material : DNA © 2022, Aakash BYJU'S. All rights reserved Nucleus  Structure : Double membrane Structure Outer membrane  May be smooth or rough  Continuous with ER, associated with ribosomes © 2022, Aakash BYJU'S. All rights reserved Inner membrane  Smooth Endoplasmic reticulum Nucleolus Chromatin Nuclear pore Nucleoplasm Nuclear envelope  Two membranes are separated by fluid filled perinuclear space (10 to 50 nm) Nucleus Structure : A nucleus in non-dividing phase is called interphase nucleus. Structure Nuclear Envelope Nucleoplasm Nucleolus  Outer membrane: Smooth or with ribosomes  Transparent, semifluid and colloidal substance  Spherical structure found in the nucleoplasm  Inner membrane: Smooth  Contains nucleolus  Site for ribosomal RNA synthesis  Separated by a space known as perinuclear space  Contains complex pores © 2022, Aakash BYJU'S. All rights reserved Chromatin  Highly, extended and diffused network of nucleoprotein fibres called chromatin Nucleus Chromatin : (Gk. chrorma - colour) Loose and diffused network of nucleoprotein fibres called chromatin Chromatin fibres condense to form chromosomes Composition: DNA, basic proteins histones, RNA and some nonhistone proteins Histone proteins are the packaging proteins Associated with packaging of DNA into compact structures called chromosomes Single human cell has approximately two-meter-long thread of DNA distributed among the chromosomes © 2022, Aakash BYJU'S. All rights reserved Chromosome Chromatin fiber Nucleosome Histone DNA Double Helix Nucleus Structure of a chromosome Has two identical halves called chromatids Held together at one point called centromere Appears as a narrow region called primary constriction of the chromosome On the sides of centromere, discshaped structures are present known as kinetochores Ends of chromosome are called telomeres Seal the ends of chromosomes and prevent shortening or chromosome loss © 2022, Aakash BYJU'S. All rights reserved Homologous chromosomes Centromeric region Sister chromatids Nucleus Classification of Chromosomes (on the basis of centromere position) Metacentric p arm Centromere q arm At the centre © 2022, Aakash BYJU'S. All rights reserved Sub-metacentric p arm Centromere Acrocentric p arm Centromere q arm Telocentric Centromere Chromosome arm q arm Slightly away from the centre Near the terminal At the terminal Nucleus Sister chromatids Non-staining secondary constrictions or NOR (nucleolar organiser) Additional constrictions near their ends Part of the chromosome beyond the secondary constriction is called satellite A chromosome having satellite is called SAT-chromosome Secondary constriction Considered as marker chromosome In humans, 5 pairs of SAT chromosomes are present © 2022, Aakash BYJU'S. All rights reserved Bands Telomere Satellite Centromere or primary constriction Nucleus Special types of chromosomes or giant chromosomes Lampbrush chromosomes Described by Ruckert (1892) Present in primary oocyte nuclei of vertebrates and invertebrates Diplotene bivalent chromosomes joined at certain points called chiasmata. Their main axis is formed by DNA. Nascent RNA molecules are present Some of these are stored as informosomes (mRNA + proteins) for future use (development of embryo). © 2022, Aakash BYJU'S. All rights reserved Salivary gland chromosomes or polytene chromosomes In insects of order Diptera (dipteran insects) Reported by E.G. Balbiani (1881) Studied in Drosophila (upto 2000 um (2 mm) another example Is Chironomus Number of chromonemata or fibrils increases upto 2000 Microbodies Many single membrane-bound minute vesicles called microbodies. Rich in enzymes. Associated with oxidation reactions other than those of respiration. Microbodies Peroxisomes Breakdown of very long chain fatty acids. Common in photosynthetic cells for photorespiration. Possess peroxide producing and peroxide destroying enzymes for peroxide biosynthesis. © 2022, Aakash BYJU'S. All rights reserved Sphaerosomes Storage and synthesis of lipids. Abundance in endosperm cells of oil seeds. These contain hydrolytic enzymes. Glyoxysomes Convert fats into carbohydrates (gluconeogenesis). Discovered by Tolbert and Beevers. Found in castor seed, groundnut seed, etc. Summary Prokaryotic cell Cell wall Pilus Capsule Plasma membrane Cytoplas m Plasmid Nucleoid (DNA) Flagella Ribosomes © 2022, Aakash BYJU'S. All rights reserved Summary Prokaryotic cell Eukaryotic cell Type of cell Always unicellular Unicellular or multicellular Nucleus Not well defined Well defined Ribosomes Smaller in size (70S) Larger in size (80S) Mitochondria Absent Present Lysosomes Absent Present Example Bacteria Animal and plant cell © 2022, Aakash BYJU'S. All rights reserved Summary Eukaryotic cell Nucleus SER Ribosomes RER Plasma membrane Lysosome Centrioles Peroxisome Plant cell Golgi apparatus Mitochondria Cytoskeleton Cytosol Animal cell Vacuole Cell wall Cell membrane Chloroplast Nucleus Endoplasmic Reticulum Ribosomes Golgi apparatus Mitochondria © 2022, Aakash BYJU'S. All rights reserved Summary Plant cell Animal cell Square or rectangular Irregular or round Cell wall Present Absent Plasma membrane Present Present Endoplasmic Reticulum Present Present Present and lies on one side of the cell Present and lies in the centre of the cell Present but are very rare Present Absent Present Cell shape Nucleus Lysosomes Centrosome © 2022, Aakash BYJU'S. All rights reserved Summary Plant cell Animal cell Golgi Apparatus Present Present Cytoplasm Present Present Ribosomes Present Present Plastids Present Absent Few large or a single, centrally positioned vacuole Usually small and numerous Absent Present in most of the animal cells Present but fewer in number Present and are numerous Vacuoles Cilia Mitochondria © 2022, Aakash BYJU'S. All rights reserved Summary Non - membrane bound organelle Centrosomes Ribosomes Single membrane bound organelles Endoplasmic reticulum Mitochondria Microbodies Peroxisome Glyoxysome Sphaerosome Plastids Chloroplast Chromoplast Leucoplast Lysosomes Nucleus Golgi Complex © 2022, Aakash BYJU'S. All rights reserved Double membrane bound organelles