Topic 1 (paper 1)

• Eukaryotic cells


  Animal and plant cells
• Structures in eukaryotic cells

  • Cell membrane
  • Cytoplasm
  • Nucleus containing DNA
• Structures in prokaryotic cells


  • Cell wall
  • Cell membrane
  • Cytoplasm
  • Single circular strand of DNA and plasmids
• What are Organelles


  Structures in a cell that have different functions
• Organelles in animal and plant cells


  • Nucleus
  • Cytoplasm
  • Cell membrane
  • Mitochondria
  • Ribosomes
• Organelles only in plant cells


  • Chloroplasts
  • Permanent vacuole
  • Cell wall
• Structures in bacterial cells


  • Cytoplasm
  • Cell membrane
  • Cell wall
  • Chromosomal DNA (circular)
  • Plasmids
  • Flagella
• Differentiation


  A process that involves the cell gaining new sub-cellular structures in order for it to be suited to its role
• Specialised animal cells


  • Sperm cells
  • Egg cells
  • Ciliated epithelial cells
• Specialised plant cells


  • Root hair cells
  • Xylem cells
  • Phloem cells
• Light microscope


  Has two lenses, usually illuminated from underneath, maximum magnification of 2000x and resolving power of 200nm
• Electron microscope


  Uses electrons instead of light, can achieve magnification up to 2,000,000x and resolving power of 10nm (SEM) and 0.2nm (TEM)
• Electron microscopes have allowed the discovery of viruses and detailed examination of proteins
• Magnification


  Magnification of the eyepiece lens x magnification of the objective lens
• Size of an object

  Size of image/magnification = size of object
• Prefixes


  • Centi (0.01)
  • Milli (0.001)
  • Micro (0.000,001)
  • Nano (0.000,000,001)
• Using a light microscope

  1. Place slide on stage

  2. Look through eyepiece

  3. Turn focus wheel

  4. Start with lowest magnification
• Preparing a slide


  1. Take thin layer of cells

  2. Add chemical stain

  3. Apply cells to slide

  4. Lower coverslip
• Enzymes


  Biological catalysts that increase the rate of reaction without being used up
• Active site


  The uniquely shaped site on an enzyme where the substrate binds
• Lock and key hypothesis

  The shape of the substrate is complementary to the shape of the active site, forming an enzyme-substrate complex
• Ion


  Measured size / actual size
• Actual size


  Measured size / magnification
• Total magnification


  Objective lens magnification x eyepiece lens magnification
• Enzymes


  Biological catalysts (a substance that increases the rate of reaction without being used up)
• Enzymes


  • Present in many reactions - allowing them to be controlled
  • They can both break up large molecules and join small ones
  • They are protein molecules and the shape of the enzyme is vital to its function
• Active site


  Where the substrate binds
• Lock and Key Hypothesis

  1. The shape of the substrate is complementary to the shape of the active site (matches the shape of the active site), so when they bond it forms an enzyme-substrate complex

  2. Once bound, the reaction takes place and the products are released from the surface of the enzyme
• Enzymes can only catalyse (speed up) reactions when they bind to a substrate that has a complementary shape, as this is the only way that the substrate will fit into the active site
• Enzyme specificity


  Enzymes can only catalyse reactions when they bind to a substrate that has a complementary shape
• Factors enzymes require


  • Optimum pH
  • Optimum temperature
  • Optimum substrate concentration
• Optimum temperature in humans

  A range around 37 degrees Celsius (body temperature)
• As temperature increases


  The rate of reaction increases up to the optimum, but above this temperature it rapidly decreases and eventually the reaction stops
• Denaturation


  When the bonds that hold the enzyme together break, changing the shape of the active site so the substrate can no longer 'fit into' the enzyme
• Optimum pH


  7 (neutral) for most enzymes, but some have a lower optimum pH
• If the pH is too high or too low


  The forces that hold the amino acid chains that make up the protein will be affected, changing the shape of the active site so the substrate can no longer fit in
• As substrate concentration increases


  The rate of reaction will increase up to the saturation point, after which increasing the substrate concentration will have no effect
• Saturation point


  The point at which increasing the substrate concentration has no further effect on the rate of reaction
• Amylase


  An enzyme that breaks down carbohydrates such as starch into simple sugars such as maltose
• Iodine (dark orange colour) can be used to check for the presence of starch in the solution