bio 127 plant cell

• cell


  basic unit of life
• robert hooke


  cork cells = dead cells = cell wall = cell:prison
• two parts of cell

  • cell wall
  • protoplast
• plant cell has the ff:

  1. cell wall
  2. plasmodesmata
  3. pits
  4. vacuole
  5. plastids
  6. glyoxysomes
• cell wall has primary pit fields, pits, & plasmodesmata
• cell wall

  • outermost part
  • rigidity
  • protection for osmotic & mechanical underlying protoplast
  • communication between cells
  • maintains shape
• wall layers


  primary and secondary
• all cells have primary walls; secondary walls for support
• primary wall

  thin & random microfibrils
• secondary wall


  parallel microfibrils
• middle lamella


  cement of Calcium pectate (gelatinous)
• cellulose microfibrils


  principal component providing tensile strength
• matrix


  cement that binds the cell wall

  • hemicellulose
  • pectin
  • proteins
  • lignin
• cellulosic components


  cellulose - repeating glucose units (cellulose microfibrils)
• food is in the form of sucrose
• cellulose is synthesized by the cellylose synthase
• cellulose synthase is found in the plasma membrane
• only the glucose component of the disaccharide sucrose is added to the growing chain of cellulose molecules
• cellulose microfibril emerges from rosette to form part of the cell wall
• non cellulosic components

  1. hemicellulose
  2. pectin
  3. extensin
  4. other proteins
• hemicellulose

  • sugar and sugar derivatives
  • cross-link of cellulose microfibrils
  • coats surface of cellulose
  • synthesizes in Golgi apparatus
• pectin

  • hydrophilic fillers & interlocking matrix gel
  • to pervent collapse & aggregation of cellulose networks
  • absorbs water
  • expands so microfibrils move away from each other
  • 35% in primary wall
  • rich galacturonic acid
  • synthesizes in the golgi apparatus
• extensin

  • glycoprotein in primary wall
  • forms structural network = adds strength
  • involved in cell growth
• extensin & expansin

  serve as structural or enzymatic functions in the cell wall
• other proteins

  • generated in Rough ER
  • modified in golgi body before cell surface
• pectins & hemicelluloses

  • assembled in golgi cisternae
  • transported to cell surface within Golgi-derived vesicles
• primary wall

  • random microfibrils
  • cellulose, hemicellulose, & some pectin
  • surface area & thickness
  • expands because of absorbing water (vacuole pushes against wall, stretching & elongating it)
  • associated with living protoplast
• pectin


  used for expansion of the wall
• secondary wall

  • parallel microfibrils
  • formed after cell elongation
  • thicker and more rigid that primary wall
  • 45% cellulose
  • less hemicellulose than PW
  • little pectic substance
  • has lignin preventing wall extension
  • stronger than microfibrils
  • phenolic alcohols
  • reduces digestibility of plant material by animals
• lignin prevents wall extension due to formation of hydrophobic matrix networks binding tightly to cellulose
• if the functions of the cell is for additional support/conduction of water, then it would form a secondary wall
• plasmodesmata

  • cytoplasm continuity is maintained between daughter cells
  • permits diffusion through cytoplasmic sleeve/cell wall
  • penetrates the cell wall for important developmental events
  • enables communication between cells
• primary pit fields and pits


  where plasmodesmata would be located
• primary pit fields are THIN on cells with primary cell walls
• pits are wall areas WITHOUT a secondary wall on cells with secondary cell wall, but still provide a route for flow of water between adjacent conduits
• protoplast

  made up of nucleus and cytoplasm; cell wall has been removed
• plasma membrane

  • semi-permeable membrane
  • allows certain material to enter
  • made up of phospholipid bilayers
  • hydrophilic head
  • hydrophobic tail
  • controlls passage in and out of protoplast
  • highly invaginated
• nucleus

  • storage
  • replication of chromosomes (DNA-protein complex)
  • enveloped by outer & inner membrane
  • nuclear lamina
  • chromatin
  • chromosomes
• nucleolus

  site of rRNA (ribosomal RNA) synthesis
• nuclear lamina

  • lined at nuclear side of nucleus
  • network of intermediate filaments
  • maintains the shape of the nucleus