topic 2

• Define Magnification


  How many times larger the image is compared to the object
• Define Resolution


  The smallest distinguishable distaince between 2 points
• How would you convert mm to micrometres?

  x1000
• How would you convert micrometers to nanometres?

  x1000
• How would you calculate the actual size of an object?

  Image/Magnification
• What is Cell Fractionation?

  The separation of the cell organelles in order to be studied
• What does Homogenisation involve?

  Cell walls are broken up using a homogeniser (blender) to release the organelles
• Why is the solution filtered after being homogenised?

  To remove any unbroken cells and large pieces of debris
• What does Ultracentrifugation involve?


  Spinning the homogenate at increasing speeds until the most dense organelle forms a pellet. The supernatant (liquid) is then put into a fresh tube and spun at a higher speed.
• Why must the homogenate be cold?

  To stop enzymes from breaking down the cell organelles.
• Why must the homogenate be isotonic?

  To prevent the cell organelles from swelling and bursting under pressure through too much osmosis.
• Why must the homogenate be buffered?

  To keep a constant pH to prevent the enzymes denaturing.
• What does a 'buffer' chemical do?

  Keeps a constant pH
• Advantage of light microscope?

  Light can pass through air so living things can be viewed

  
  

  Staining is not essential

  
  

  There are few artefacts
• Disadvantages of light microscope?

  Low resolution - 0.2μm

  
  

  Only produces a 2D image
• Advantage of TEM?


  Has the strongest magnification

  
  

  Highest resolution - 0.1nm
• Disadvantage of TEM?


  Electrons cannot pass through air so vacuum needed

  
  

  Only very thin sections can be used as electrons do not penetrate far

  
  

  Only produces a 2D image

  
  

  Staining essential

  
  

  Lots of artefacts
• Advantage of SEM?


  Produces a 3D image

  
  

  Fewer artefacts compared to a transmission electron microscope

  
  

  Electrons can be used to scan he surface of specimens
• Disadvantage of SEM?


  Better resolution compared to a light microscope but a worse one compared to a transmission electron microscope - 20nm

  
  

  Staining essential

  
  

  Electrons cannot pass through air so vacuum needed
• What limits the magnification and resolution of a light microscope?

  Light has a long wavelength, and so, by electrons having a shorter wavelength, they have a greater resolving power
• What is an eyepiece graticule?

  A glass disc with a scale etched onto it to help measure objects down a microscope. It is 10mm long divided into 100 subdivisions. It can be calibrated using an stage micrometer.
• What is a Eukaryotic Cell?

  Membrane bound nucleus

  
  

  DNA is bound together by proteins (histones) into chromosomes.

  
  

  Contain an endoplasmic reticulum and numerous specialized organelles not present in prokaryotes (mitochondria, Golgi bodies, and lysosomes)
• What is the function of the nuclear envelope?

  A double membrane which surrounds the nucleus which controls the entry and exit of materials through nuclear pores (such as RNA for protein synthesis)
• What is chromatin?


  The DNA found within the nucleoplasm. This is unbranched form of chromosomes when the cell is not dividing.
• What is the function of the nucleolus?


  A small spherical body within the nucleoplasm that manufactures ribosomal RNA and sites ribosome production
• What are the main functions of the nucleus?


  Control centre of the cell through the production of mRNA and hence protein synthesis

  
  

  Contains genetic material in the form of chromatin or chromosomes

  
  

  Manufacture ribosomal RNA and ribosomes
• What is Rough Endoplasmic Reticulum?


  Series of membrane bound flattened sacs with ribsomes on the surface.
• Functions of the Rough Endoplasmic Reticulum?

  Provides a large surface area for attachment of ribosomes

  
  

  Folds and processes proteins
• What is Smooth Endoplasmic Reticulum?


  System of membrane bound sacs. Less common than Rough ER and not found near the nucleus.
• What is the function of the Smooth Endoplasmic Reticulum?

  Produces and processes lipids
• What is the Golgi Apparatus?

  A series of fluid filled and flattened sacs with vesicles on the edges
• What is the function of the Golgi Apparatus?


  They modify and package proteins (from RER) and lipids (from SER) into vesicles so they can travel through the cytoplasm to their destination. In short they:

  1. Add carbohydrates to proteins (forming glycoprotein)

  2. Produce secretory enzymes (in the pancreas)

  3. Secrete carbohydrates (for making cell walls in plants)

  4. Transport, modify and store lipids

  5. Produce lysosomes
• Functions of lysosomes?


  Inside phagocytes they breakdown pathogens

  To breakdown worn out cell organelles

  Produce digestive enzymes
• What is the function of the double membrane inside mitochondria?

  Controls entry and exit of material. The inner membrane is folded to form extensions known as cristae.
• What is the function of the cristae inside the mitochondria?

  They provide a large surface area for enzymes to attach to
• What is the function of the matrix inside the mitochondria?

  Enzymes involved in respiration are found here
• Describe the structure of ribosomes and their function:

  They are made up of 2 subunits (one small and one large) both made of ribosomal RNA and protein. There are two types:

  80S type - eukaryotic cells

  70S type - prokaryotic cells

  They are important in protein synthesis
• List the seven main eukaryotic cell organelles in order of size from largest to smallest:

  1. Nucleus

  2. Rough ER

  3. Smooth ER

  4. Golgi Apparatus

  5. Mitochondria

  6. Lysosomes

  7. Ribosomes
• What are the functions of the cell wall?

  Gives rigidity and strength to cell

  
  

  Prevents plant cell from swelling and bursting

  
  

  Gives mechanical strength to individual cell and whole plant

  
  

  Gives each cell its own unique shape
• What are cell walls in plants made up of?

  Cellulose microfibrils.