Organelles

• Chloroplasts


  • Large, oval-shaped with double membrane
  • Contains stacked membranes (thylakoid membranes), have chlorophyll attached; absorb light for photosynthesis
  • Also matrix, DNA and ribosomes; Endosymbiotic Theory
• Golgi Body


  • Flattened tubes and vesicles transportation (cisternae)
  • Receives tansport vesicles from SER (lipids) and RER (proteins)
  • Adds final touches
  • Forms secetory vesicles; for exocytosis or in-cell transport
• Lysosomes


  • Round with no clear internal structure
  • Contains digestive enzymes (mostly hydrolases in acidic solution)
  • Involved in hydrolysis of worn cells and large molecules
  • Abundant in secretory cells and phagocytic leukocytes
• Mitochondria


  • Large, oval-shaped with double membrane
  • Inner membrane folds into cristae
  • Inside is matrix, contains; respiratory enzymes, mitochondrial DNA and ribosomes
  • Site of aerobic repsiration
  • Inherited from Mother
  • Endosymbiotic Theory: Original mitochondria was a bacteria, that got absorbed
• Nucleus


  • Contains linear DNA wrapped around histones
  • DNA + Histones = Chromatin
  • Controls cell activity using proteins synthesised by genetic code
  • Has 1-2 nucleoli (sing. nucleolus); made of RNA, DNA and proteins; synthesises ribosomes
  • All rest is nucleoplasm
  • Surrounded by double membrane (nuclear envelope), continuous with RER and porous (nuclear pores)
  • Allows large molecules out; e.g. RNA, but not DNA (histones make it too bulky)
• Ribosomes


  • Smallest, most complex
  • Eukaryotes: 80s, Prokaryotes: 70s
  • Two subunits (large and small); both made of equal-ish quantities of rRNA and protein
  • Either free in cytoplasm or bound to RER
  • Site of protein synthesis
• Vacuole


  • Membrane-bound sac containing dilute solutions (tonoplast)
  • Small ones in most (eukaryotic) cells
  • Plant cells have a large permanent one; fills most of cell contining cell sap, to maintain turgidity
• Cytoskeleton


  • Make structural units, network of 3 protein fibres:

  Microfilaments:

  • Made of actin
  • Contractile protein, give structure and movement
  • Just under plasma membrane

  Intermediate Filaments:

  • Give mechanical filaments
  • Maintain organelles postions

  Microtubules:

  • Transport materials around cell
  • In conjunction with motor proteins
  • Tubulin dimers form long chains; 13 chains form one microtubule
  • Make up centrioles, cilia, and flagellum (in eukaryotes)
• Mesosome


  • Prokaryotic, remeniscient of mitochondria/chloroplast inner membrane
  • Tightly folded region of cell membrane, with many proteins; giving large surface area
  • Site of aerobic respiration (and photosynthesis in cyanobacteria)
  • Also involved in cell division
• Nucleoid


  • Circular (closed loop) double-stranded DNA
  • Associated with proteins (not histones)
  • Sometimes called bacterial chromosome
  • Has all genes to code for all bacterial proteins
• Plasmids


  • Small DNA circle (separate from main loop)
  • Transfer between bacteria cells in conjugation
  • Antibiotic resistance genes occur on plasmids
  • Also used extensively as vectors in genetic engineering
• Endospores


  • Unique (circumstantial structure)
  • Allow for a certain dormancy level; tough, non-reproductive
  • Formed by some gram-positive in environmental conditions are unfavourable
  • For survival and protection of dormant bacteria from high temperature, desiccation and UV radiation
• Outer Layers

  Capsule/Slime Layer

  • Common, not always present
  • Prokaryotic
  • Thick polysaccharide layer out cell wall
  • Protects against desiccation + phagocytosis

  Plasma Membrane

  • Phospholipid bilayer with imbedded molecules, e.g. receptors molecules; proteins, glycoproteins + glycolipids)
  • Eukaryotic + prokaryotic
  • Controls entry/exit of molecules; partial permeability

  Cell Wall

  • Rigid, Supportive
  • Keeps cell shape
  • Plants: Made of cellulose; held by protein + hemicellulose matrix
  • Prokaryotes: Made of polysaccharides; main 1 is peptidoglycan
  • Maintains turgidity; stops bursting from osmotic pressure
• Filaments

  Centrioles

  • Small hollow cylinders
  • Made microtubules
  • Synthesise + organise spindle fibres
  • Animal cells

  Flagellum

  • Eukaryotes:
  • Longer Cilia
  • Conract to move
  • Made of tubulin protein
  • Energy from ATP
  • Prokaryotes:
  • Thinner (no 9+2)
  • Contract to move
  • Made of flagellin protein
  • Energy from chemiosmosis

  Cilia

  • Hair-like projections on cell surface membrane
  • Present sometimes in Animal cells
  • Made microtubules (in 9+2 arrangement)
  • Contract + move substances (e.g. in trachea or oviducts)

  Pili/Fimbriae

  • Protein filaments sticking out from cell wall
  • Pili helps conjunction
  • Fimbriae help bacteria stick to each other, form colonies, or to other surfaces, form biofilms
• Endoplasmic Reticulum

  Smooth

  • Dense system of flattened tubes with fluid-filled space (cisternae)
  • Site of lipid + steroid synthesis
  • Abundant in hepatocytes, intestinal epithelium, adrenal cortex + skin sebaceous glands

  Rough

  • Dense system of flattened tubes with fluid-filled space (cisternae)
  • Ribosomes embedded on surface
  • Involved in protein synthesis + secretion
  • Abundant in enzyme-secreting + rapidly growing cells
  • Continuous with nuclear envelope to increase efficiency