Cells

• Prokaryotes

  • smaller in size
  • no complex membrane-bound organelles
  • chromosomal DNA found free in the cytoplasm
  • DNA is circular
  • smaller ribosomes
  • extra-chromosomal DNA/plasmids
  • peptidoglycan cell wall
  • slime capsule
  • no centrioles/microtubules/spindle fibres
• Eukaryotic

  • animals, plants and fungi
  • cell surface membrane
  • cytoplasm
  • organelles/membrane systems
  • animal crells=irregular shapes
  • plant/fungi=more regular
• Nucleus

  • largest organelle
  • contains DNA in chromosomes that code for the production of rRNA
  • histones help support and protect the DNA
  • chromosomes usually found in diffuse state/chromatin
  • heterochromatin: darker regions, DNA not transcribed
  • euchromatin: lighter regions, DNA transcribed
• Nucleus

  • surrounded by a nuclear envelope
  • large molecules can enter/exit via nuclear pores
  • outer membrane is extended into cisternae and encrysted with ribosomes
  • DNA code must be taken to sites of protein synthesis in cytoplasm, DNA transcribed leaves via nuclear pores
• Endoplasmic reticulum


  3D membrane system encloses sacs- cisternae
• Rough Endoplasmic Reticulum

  • continuation of outer membrane of nuclear envelope
  • ribosomes dotted along cytoplasmic side
  • facilitates transport of mRNA from nucleus to ribosomes
  • once primary structure is synthesised, secondary/tertiary develop in cisternae
  • proteins are packaged into vesicles for transport
• Smooth Endoplasmic Reticulum

  • no ribosomes, not responsible for protein synthesis
  • site of lipids and steroid synthesis
  • detoxification of drugs
• Ribosomes

  • small organelles
  • found either free in cytoplasm or attached to RER
  • made of protein and rRNA
  • occur in groups/polyribosomes
• Golgi Apparatus

  • series of cisternae
  • vesicles containing newly synthesised proteins pinch off from RER and fuse with the convex and leave by the concave face
  • Golgi modifies proteins arriving from the RER
  • modifications: addition of lipid/lipoprotein, addition of carbohydrate/glycoprotein
  • addition of cofactors
  • combining of polypeptides to form quaternary structure
  • labelling packaging and sorting for exocytosis
• Mitochondria

  • possess a mitochondrial envelope with an intermembrane space
  • intermembrane infolded into multiple cristae
  • cristae provide a larger membrane area to embed enzymes needed for reactions of respiration
  • cristae extend into mitochondrial matrix
  • site of respiration and production of ATP
• Lysosomes

  • tiny vesicles formed by golgi
  • contain hydrolytic enzymes
  • fuse with other vesicles containing something o be destroyed
• Microtubules

  • hollow cylinders formed from tubulin
  • form the cytoskeleton
  • provide a network for transporting substances in a cell
  • spindlefibres formed in microtubules, moving chromosomes
  • centrioles involved in assembly of cell spindle fibres during mitosis
• Cell surface (plasma) membrane

  • Phospholipid bilayer and proteins
  • Fluid ( phospholipids may move from side-to-side)
  • Mosaic (protein molecules are irregularly arranged)
  • extrinsic/intrinsic/transmembrane protein
•  Phospholipid bilayer

  • hydrophilic head, hydrophobic tail
  • selectively permeable
  • cholesterol increases membrane stability at high temp and at low temp increases fluidity
• Membrane proteins

  • stabiolse1the membrane
  • transmembrane protein act as channels
  • transmembrane protein/glycoprotein act as carriers aiding transport of charged molecules against conc. gradient
  • glycocalyx always found on the outside of the cell membrane made up of polysaccharides attached to glycoproteins or lipoproteins
  • glycoproteins and glycolipids can hydrogen bond and stabilise the membrane further
• Plant cell

  • don't have lysosomes/centrioles
  • protoplast surrounded by a fully permeable cellulose cell wall
• • primary cell wall is made of microfibrils orientated in different directions and in a loose arrangement to allow the cell wall to expand as it grows
  • secondary cell wall made of microfibrils orientated in he same direction but different layers in opposite direction, giving strength
  • middle lamella is composed of calcium pectate that holds cells together
• Plasmodesmata


  channels between cytoplasm of two adjacent cells

  cells are connected physically and metabolically
• Chloroplasts

  • site of photosynthesis
  • possess a chloroplast envelope
  • within the chloroplast is the fluid-filled membrane called the stroma
  • thylakoids appear singly and in stacks known as grana
  • thylakoids contain chlorophyll and have a large surface area to absorb light energy and accomodate as many chlorophyll molecules as possible
  • large starch grains
  • lipid droplets
• Vacuole


  Plant cells have a large permanent vacuole surrounded by the tonoplast

  Important in storage of water and ions
• Fungal cells

  • protoplasm surrounded by chitin cell wall
  • contain vacuoles but no chloroplasts
  • possess lysosomes and store carbohdrate as glycogen
  • multinucleate
  • elongated cells
• Light microscope-Advantages

  • cheap and easy to operate
  • small and portable
  • unaffected by magnetic fields
  • preparation of sample material is quick and simple
  • sample rarely distorted
  • natural colour may be observed
  • living specimens may be observed
• Light microscope-disadvantages

  • magnifies up to x2000
  • depth of field is restricted
• Electron microscope-disadvantages

  • expensive to purchase and operate
  • very large and not portable
  • affected vby magnetic fields
  • preparation of material is lengthy
  • preparation may distort sample
  • black and white
  • living specimens and biological processes may not be observed
• Electron microscope-advantages

  • magnifies up to x1000000
  • allows greater depth of field