cell unit of life

• Cell

  The fundamental structural and functional unit of all living organisms
• Cell

  • Is the unit of life
  • Anton von Leeuwenhoek first saw and described a live cell
  • Robert Brown discovered the nucleus
  • Schleiden and Schwann together formulated the cell theory
  • 'Omnis cellula-e-cellula' was explained by Rudolf Virchow
• Eukaryotic cells

  Cells that have membrane bound nuclei
• Prokaryotic cells


  Cells that lack a membrane bound nucleus
• Ribosomes are non-membrane bound organelles found in ALL cells
• Mycoplasma

  • The smallest cell, 0.3 μm in length
• Basic shapes of bacteria

  • Bacillus (rod-like)
  • Coccus (spherical)
  • Vibrio (comma-shaped)
  • Spirillum (spiral)
• Eukaryotic cell

  • Typical size is 10-20 μm
• Many bacteria have small circular DNA in addition to genomic DNA and is called plasmid
• Mesosome


  The infolding of cell membrane in bacteria
• Glycocalyx

  The cell envelope of prokaryotic cells, consisting of three layers: capsule, cell wall, and plasma membrane
• In some prokaryotes, glycocalyx could be a loose sheath called slime layer or a thick and tough layer called capsule
• Cell wall determines the shape of cell and provides structural support in bacteria
• Cyanobacteria


  • The membranous extensions into cytoplasm called chromatophores contain pigments
• Surface structures present in bacteria

  • Flagella
  • Pili
  • Fimbriae
• Bacterial flagella

  • Composed of three parts: filament, hook, and basal body
  • Filament is the longest portion and extends from cell surface to the outside
• Prokaryotic ribosome

  About 15-20 nm in size, made up of 30S and 50S subunits forming 70S ribosome
• Polyribosome/Polysome


  Several ribosomes attached to a single mRNA, forming a chain
• Reserve material in prokaryotic cells are stored in cytoplasm in the form of inclusion bodies
• Cell membrane

  Composed of lipids arranged in a bilayer
• In humans, the membrane of the erythrocyte has approximately 62% protein and 40% lipids
• Fluid mosaic model

  Describes the quasi-fluid nature of lipids enabling lateral movement of proteins within the overall bilayer, proposed by Singer in 1972
• Osmosis

  Movement of water by diffusion across plasma membrane
• Active transport


  Example: Na/K pump
• Plant cell wall

  • Primary wall is capable of growth, and secondary wall is formed on the inner side of cell
  • Middle lamella is a layer made up of calcium pectate which glues neighbouring cells together
  • Plasmodesmata connect the cytoplasm of neighbouring cells
• Endomembrane system

  • Cell organelles such as Lysosome
• Rough endoplasmic reticulum (RER)

  ER bearing ribosomes on their surface
• Smooth endoplasmic reticulum (SER)

  Major site of synthesis of lipids
• Golgi apparatus

  • Golgi cisternae are concentrically arranged near the nucleus with distinct convex cis face and concave trans face
  • Vesicles from the ER fuse with cis face of Golgi and move towards maturing trans face
  • Important site of formation of glycoproteins and lipids
• Lysosomal vesicles

  Rich in hydrolytic enzymes that are optimally active in acidic pH
• Vacuole

  Bound by a single membrane called tonoplast
• In Amoeba, the Contractile vacuole is important for excretion and in protists cell vacuole are formed by engulfing the food particles
• Mitochondria and Chloroplast

  • Double membrane-bound structures
• Mitochondrial matrix

  The inner compartment of mitochondria
• Mitochondria organelle is the site of aerobic respiration and it divides by fission
• Types of plastids

  • Chloroplasts
  • Chromoplasts
  • Leucoplasts
• Amyloplast type of leucoplast stores carbohydrates, aleuroplast store proteins
• Chlamydomonas


  • A green algae has one chloroplast per cell
• Stroma

  The space limited by inner membrane of chloroplast
• Grana

  Thylakoids arranged in stacks like piles of coins