Cells

• What are the two main types of microscopes used for studying cells?


  Light microscopes and electron microscopes
• How do light microscopes resolve images?


  They use a pair of convex glass lenses
• What is the resolution limit of light microscopes?


  0.2 µm
• Why is the resolution of light microscopes limited to 0.2 µm?


  Because it is the wavelength of light
• What is the resolution limit of electron microscopes?


  0.1 nm
• What is the formula for calculating magnification in microscopy?


  Magnification = size of image / size of real object
• How is resolution defined in microscopy?


  As the minimum distance apart that two objects can be distinguished as separate
• What is the main advantage of electron microscopes over light microscopes?


  They can resolve objects closer than 0.2 µm apart
• What are the two main types of electron microscopes?


  Transmission electron microscopes (TEM) and scanning electron microscopes (SEM)
• How do transmission electron microscopes (TEM) work?


  A beam of electrons passes through a thin section of a specimen
• What happens to areas that absorb electrons in a TEM?


  They appear darker on the electron micrograph
• How does a scanning electron microscope (SEM) create a 3D image?


  By scanning a beam of electrons across the surface and analyzing the scattering pattern
• What is a limitation of using electron microscopes?


  The whole system must be in a vacuum, so living specimens cannot be observed
• What is required for preparing specimens for electron microscopy?


  A complex staining process is needed
• Why must specimens be very thin for TEM?


  So that the electrons can pass through
• How does the resolving power of SEM compare to TEM?


  SEM has a lower resolving power than TEM
• What is cell fractionation and how is it commonly performed?


  • Cell fractionation separates different parts and organelles of a cell.
  • The most common method is differential centrifugation.
• What are the steps involved in homogenization during cell fractionation?


  1. Cells are blended in a homogeniser to form homogenate.
  2. The homogenate is spun at a slow speed in a centrifuge.
  3. Heaviest organelles (nuclei) form a pellet at the bottom.
  4. Supernatant is removed and spun faster to sediment the next heaviest organelle (mitochondria).
  5. This process continues to separate organelles by increasing speed.
• Why is the homogenate placed in a cold, buffered solution?


  To prevent organelles from bursting and to maintain pH
• What are the common features of eukaryotic cells?


  • Contain a nucleus
  • Have membrane-bound organelles
• What is the ultrastructure of the nucleus in eukaryotic cells?


  It has a double membrane called the envelope with ~3000 nuclear pores
• What is the function of the nucleolus?


  It is the site of ribosome production
• What is the role of rough endoplasmic reticulum (RER)?


  It folds and processes proteins made on the ribosomes
• What is the function of smooth endoplasmic reticulum (SER)?


  It produces and processes lipids
• What does the Golgi apparatus do?


  It processes and packages proteins and lipids
• What is the structure of mitochondria?


  They are oval-shaped with a double membrane and folded inner membrane called cristae
• What is the function of centrioles?


  They are involved in producing spindle fibers for cell division
• What are ribosomes composed of?


  Two subunits
• What do lysosomes contain?


  Digestive enzymes
• What is the cell wall of prokaryotic cells made of?


  Peptidoglycan
• What is the function of the capsule in prokaryotic cells?


  It helps the cell retain moisture and adhere to surfaces
• What is a plasmid?


  A circular piece of DNA
• What is the function of the flagellum in prokaryotic cells?


  It rotates to move the cell
• What are pili in prokaryotic cells?


  Hair-like structures that attach to other bacterial cells
• What are mesosomes in prokaryotic cells?


  Infoldings of the inner membrane containing enzymes for respiration
• What are viruses composed of?


  Nucleic acid enclosed in a protein coat called the capsid
• How are cells organized in multicellular organisms?


  Cells are organized into tissues, tissues into organs, and organs into systems
• What is the role of mitosis in the cell cycle?


  • Produces identical daughter cells for growth and asexual reproduction.
  • All cells produced are genetically identical, leading to no genetic variation.
• What are the three stages of the cell cycle?

  1. Mitosis
  2. Interphase
  3. Cytokinesis
• What are the four stages of mitosis?


  Prophase, metaphase, anaphase, and telophase