key concepts

• Eukaryotic cells


  Animal and plant cells
• Prokaryotic cells


  Bacterial 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
• 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
• Standard form


  Multiplying a number by a power of 10 to get bigger or smaller, with the 'number' between 1 and 10
• Orders of magnitude


  Understanding how much bigger or smaller one object is compared to another
• 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
• 1.7, 1.8 and 1.9 - Enzymes: Mechanisms, Denaturation and Factors Affecting Enzyme Activity
• 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. 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
• Enzyme specificity


  Enzymes can only catalyse 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
• Enzymes


  • Require an optimum pH and temperature
  • Need an optimum substrate concentration
• Optimum temperature

  In humans is 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


  For most enzymes is 7 (neutral), but some that are produced in acidic conditions, such as the stomach, have a lower optimum pH
• As substrate concentration increases


  The rate of reaction will increase - up to a point (the saturation point)
• 1.10 - Core Practical - Effect of pH on Enzyme Activity