cell

• Robert Hooke


  • Discovered cell
  • Cork cells discovered by Hooke
• Anton Von Leeuwenhoek


  • First observed and described a live cell
• Theodore Schwann


  • Reported that cells had a thin outer layer (plasma membrane)
  • Found that plant cells have cell wall
• Rudolf Virchow


  • Explained that cells divided and new cells are formed from pre-existing cells (Omnis cellula-e cellula)
  • Modified the cell theory
• Statements of Cell Theory

  • All living organisms are composed of cells and products of cells
  • All cells arise from pre-existing cells
• Cytoplasm


  Semi-fluid matrix where cellular activities and chemical reactions occur, keeps the cell in 'living state'
• Ribosomes


  Non-membrane bound organelles found in cytoplasm, chloroplasts, mitochondria and on rough Endoplasmic Reticulum
• Cell sizes


  • Smallest cells: Mycoplasmas (0.3 μm in length)
  • Largest isolated single cell: Egg of ostrich
  • Longest cells: Nerve cell
  • Size of bacteria: 3 to 5 μm
  • Human RBCs: 7.0 μm in diameter
• Cell types


  • Prokaryotic cells
  • Eukaryotic cells
• Prokaryotic cells


  • Have no membrane bound nucleus and organelles
  • Generally smaller and multiply more rapidly than the eukaryotic cells
  • Vary in shape & size
• Bacterial shapes


  • Bacillus (rod like)
  • Coccus (spherical)
  • Vibrio (comma shaped)
  • Spirillum (spiral)
• Prokaryotic cell organelles


  • Cell envelope
  • Mesosome & Chromatophores
  • Nucleoid
  • Flagella
  • Pili and Fimbriae
  • Ribosomes
  • Inclusion Bodies
• Cell envelope


  Chemically complex protective covering made of 3 tightly bound layers: Glycocalyx, Cell wall, Plasma membrane
• Glycocalyx


  Outer layer, composition and thickness vary in different bacteria, may be a slime layer or capsule
• Cell wall


  Middle layer, seen in all prokaryotes, gives shape to the cell and provides structural support
• Plasma membrane


  Inner layer, semi-permeable in nature and interacts with the outside, structurally similar to eukaryotes
• Bacteria types based on cell envelope

  • Gram positive
  • Gram negative
• Mesosome


  Formed by the infolding of plasma membrane, includes vesicles, tubules & lamellae
• Functions of Mesosome


  • Cell wall formation
  • DNA (chromosome) replication
  • Distribution of chromosomes to daughter cells
  • Respiration and secretion
  • Increase surface area of plasma membrane and enzymatic content
• Chromatophores


  Pigment-containing membranous infoldings in some prokaryotes, e.g. cyanobacteria
• Nucleoid


  Formed of non-membranous (naked) circular genomic DNA (single chromosome/ Genetic material) & protein
• Plasmid


  Small circular DNA outside the genomic DNA, gives some unique phenotypic characters to bacteria
• Flagella


  • Thin filamentous extensions from the cell wall of motile bacteria, have 3 parts: filament, hook & basal body
• Pili


  Elongated tubular structures made of a special protein (pilin), have no role in motility
• Fimbriae


  Small bristle like fibres sprouting out of the cell, help to attach the bacteria to rocks in streams and to the host tissues
• Ribosomes


  Associated with plasma membrane of prokaryotes, made of two subunits - 50s and 30s units, form 70S prokaryotic ribosomes
• Function of Ribosomes


  • Site of translation (protein synthesis)
  • Several ribosomes may attach to a single mRNA to form a polyribosome (polysome)
• Inclusion Bodies


  Non-membranous, stored reserve material seen freely in the cytoplasm of prokaryotic cells, e.g. phosphate granules, cyanophycean granules, glycogen granules, gas vacuoles
• Eukaryotic cells


  • Have well organized membrane bound nucleus and organelles
  • Presence of membranes gives clear compartmentalization of cytoplasm
  • Have complex locomotory & cytoskeletal structures
  • Genetic material is organized into chromosomes
• Cell organelles in eukaryotic cells

  • Cell membranes
  • Cell wall
  • Endomembrane system (Endoplasmic reticulum, Golgi apparatus, Lysosomes, Vacuoles)
  • Mitochondria
  • Plastids
  • Ribosomes
  • Cytoskeleton
  • Cilia and Flagella
  • Centrosome and Centrioles
  • Nucleus
  • Microbodies
• Cell membrane


  Composed of a lipid bilayer, protein & carbohydrate, ratio of protein and lipid varies in different cells
• Integral proteins


  Partially or totally buried in membrane
• Peripheral proteins


  Lie on the surface of membrane
• Cell membrane


  Composed of a lipid bilayer, protein & carbohydrate
• Lipids (mainly phosphoglycerides)


  • Outer polar head and inner hydrophobic tails
  • Non-polar tail of saturated hydrocarbons is protected from aqueous environment
• Components of cell membrane

  • Lipid
  • Protein
  • Carbohydrate
  • Cholesterol
• Glycoprotein


  Protein with carbohydrate attached
• Glycolipid


  Lipid with carbohydrate attached
• Fluid Mosaic Model of Cell Membrane was proposed by Singer & Nicolson (1972)
• Fluid Mosaic Model


  • Quasi-fluid nature of lipid enables lateral movement of proteins within the overall bilayer
  • Ability to move within the membrane is measured as its fluidity