1. Cell Structure

• The Cell Theory

  1. All living things are made of cells
  2. Cells are the basic structural and functional units of organisms
  3. All cells come from pre-existing cells
• Prokaryotic


  Unicellular and lacking membrane-bound organelles
• Unicellular


  Consist of only one cell that has to perform all functions
• Eukaryotic


  Multicellular and contains a nucleus and membrane-bound organelles
• Multicellular


  Consist of many different cells, each with a specific structure and function
• Prokaryotes

  • Less complex and are smaller
  • More than eukaryotic cells
  • No true nucleus or other membrane-bound organelles
  • E.g. bacteria and archaea
  • ALWAYS unicellular
  • Four main structures: cell membrane, cytoplasm, ribosomes and genetic material
• Eukaryotes

  • Contains a nucleus and membrane-bound organelles
  • E.g. animals, plants, fungi and protozoa
  • Unicellular or multicellular organisms
  • Each organelle has a specific function within the cell
• Structures in both prokaryotes & eukaryotes

  • Cell membrane, cytoplasm and ribosomes (for protein production)
• Prokaryote (2)


  DNA storage

  • Free-floating in the cytoplasm
  • Long circular nucleoid and smaller plasmids
  • Found mainly as a large loop called the bacterial chromosome

  Membrane-bound organelles

  • None (therefore there is no nucleus)

  Cell wall

  • Present in all bacteria and archaea

  Size

  • 0.1-0.5 μm
• Eukaryote

  DNA storage

  • Located in the nucleus
  • Composed of multiple chromosomes

  Membrane-bound organelles

  • Many e.g. nucleus, Golgi apparatus, endoplasmic reticulum

  Cell wall

  • Found only in plants, fungi and some protists

  Size

  • 10-100 μm
• Cells can only function with their organelles
• Structures found in both plant and animal cells

  Plant cell

  • Cell wall
  • Chloroplasts
  • Large, permanent vacuole

  Animal cell

  • Lysosomes
  • Small, permanent vacuole

  Both

  • Cell membrane
  • Cytoplasm
  • Cytoskeleton
  • Nucleus
  • Mitochondria
  • Endoplasmic reticulum
  • Golgi body
  • Ribosomes
• • Unicellular organisms - consist of only one cell that has to perform all functions
  • Multicellular organisms - consist of many different cells, each with a specific structure and function
  • This is known as cell specialisation - the process by which cells become specialised in order to perform different functions
• Light microscope

  Uses light to visualise cells
• Light microscope

  • Contains magnifying glasses inside the ocular (eyepiece) lens and objective lens that provide magnification and resolution for improved cell visualisation
  • Allows us to alter the brightness or intensity of the light
• Magnification


  Ratio of enlargement (or reduction) of an image
• Calculate total magnification: power of the objective lens (10X, 40X, 100X) and multiply by the power of the eyepiece (10X)
• Resolution


  Ability of the lens to show the fine details of the specimen viewed (distinguishes between two objects)
• The higher the resolution, the easier it will be to identify the structure in a cell
• Field of View

  • Area visible to you when looking through the microscope
  • Can calculate the size of the cell
• Course focus knob


  Change the focus and bring things into resolution faster
• Fine focus knob


  Minor changes
• Stereo microscope

  • 3D image
  • Poor resolution due to the distance between the lens and object
  • Use reflected light - light source should not be left on for too long if viewing a live specimen as the heat can kill the organism
  • Magnify x10 to x40
• Electron microscopes

  • Uses beams instead of light
  • Scanning electron microscope - scans the surface of the specimen (3D image)
  • Transmission electron microscope - produces images of internal organelles (2D image)
  • Staining techniques (e.g. dyes) allow for the staining of different cellular structures
  • Lighting techniques (e.g. phase-contrast microscopy) allow scientists to gain improved image quality of cells
  • Phase-contrast enhances the contrast to allow visualisation of cell contents
• Intracellular fluid

  • A.K.A cytosol
  • The liquid found inside the cell
  • Comprises a mixture of organelles, proteins and ions

  Extracellular fluid

  • All body fluids outside the cell; surround all cells in the body
  • Two primary constituents
  • Fluid component of the blood (plasma)
  • Interstitial fluid (IF) that surrounds all cells not in the blood - acts as a connecting link between the blood and the cells
  • Cell membrane - separates the intracellular fluid from the extracellular fluid
• Define 'cell membrane'

  A semipermeable barrier that controls the movement of substances into and out of the cell’s internal environment [between cytoplasm (intracellular) and extracellular environment]
• • Fluid mosaic model’ - used to describe the arrangement of cell membranes
  • Composed of a phospholipid bilayer (2 layers) with various proteins designed to provide a physical barrier between the extracellular and intracellular environment
• The fluid part of the cell membrane is composed of two layers of phospholipids, forming a phospholipid bilayer
• Hydrophilic head ('WATER-LOVING')

  • Forms the outside and inside lining of the cell membrane
  • Made up of phosphate heads
  • Attracted to water
• Hydrophobic tail ('WATER-HATING')

  • Made up of fatty acids (fatty acid chains)
  • Repels water
  • Inability to dissolve in water
• Hydrophilic heads are on the outside and inside, ‘hiding’ the hydrophobic tails within the bilayer
• • Cell membranes are fluid structures
  • Allows cells to change shape and grow, allowing the cell membrane to break and reform during cell division
• • Transport protein - assists the movement of substances in and out of the cell
  • The cell membrane is composed of a phospholipid bilayer with various proteins
  • Proteins are either permanently or temporarily attached to the membrane
  • Integral proteins - permanently attached to the membrane
  • Peripheral proteins - temporarily attached on the innermost or outermost surface of the phospholipid bilayer