Ultrastructure

• Common structures in both animal and plant cells:

  • Cell membrane
  • Smooth endoplasmic reticulum
  • Nucleus
  • Nucleolus
  • Golgi body
  • Rough endoplasmic reticulum
  • Lysosomes
  • Mitochondria
  • Ribosomes
  • Cytoplasm
• Specific structures found only in animal cells:

  • Centrioles
  • Lysosomes
• Specific structures found only in plant cells:

  • Cell wall
  • Chloroplasts
  • Vacuole
• The nucleus is surrounded by a double membrane with pores in the nuclear envelope that allow mRNA to exit
• The nucleolus is a dense area in the nucleus that produces ribosomes
• Chromatin in the nucleoplasm is uncondensed DNA that condenses into chromosomes during division
• Chloroplasts contain thylakoid membranes with photosynthetic pigments for photosynthesis
• Mitochondria are the site of aerobic respiration, producing ATP as the cell's energy currency
• The rough endoplasmic reticulum has ribosomes for protein synthesis, while the smooth endoplasmic reticulum synthesizes and processes lipids
• Ribosomes are made of ribosomal RNA and protein, and can be free or bound to the rough endoplasmic reticulum
• The Golgi body modifies and packages proteins and lipids for secretion out of the cell
• Lysosomes are vesicles containing digestive enzymes called lysozymes
• The cell wall in plants is made of cellulose, providing structural support and preventing bursting due to turgor pressure
• The vacuole contains water with dissolved sugars and salts, helping maintain turgor pressure and cell rigidity
• Eukaryotic cells are adapted for various functions, including maximizing diffusion with microvilli, storage with large lipid stores, and secretion with large Golgi bodies
• Cells with increased energy requirements have many mitochondria to produce ATP, such as muscle cells or cells carrying out active transport
• Prokaryotic cells have similarities and differences compared to eukaryotic cells
• Features of prokaryotic cells:

  • Cell membrane
  • Cell wall made of glycoprotein called murine
  • Cytoplasm
  • 70s ribosomes
  • Circular loop DNA in the nucleoid region
  • Lack of membrane-bound organelles
• Bacterial cells contain plasmids with useful genes like antibiotic resistance
• Capsule: mucus-like substance that protects bacteria from drying out and chemicals
• Flagellum: hair-like structure that allows bacteria to move and swim
• Viruses have different structures but share common features:

  • Attachment proteins
  • Capsid surrounding nucleic acid (DNA or RNA)
  • Envelope (present in some viruses)
• Viruses are not cells, not living, and replicate inside a living host cell
• Common units used: millimeters, micrometers, nanometers

  • To convert:
  • Millimeters to micrometers: x1000
  • Micrometers to nanometers: x1000
  • Nanometers to micrometers: /1000
  • Micrometers to millimeters: /1000
• Parts of an optical microscope:

  • Eyepiece
  • Base
  • Light source (mirror or lamp)
  • Course focus wheel
  • Fine focus wheel
  • Objective lenses
  • Stage
  • Slide clip
• Optical microscopes use a convex glass lens with eyepiece and objective lenses
• Resolution is different from magnification:

  • Resolution is the ability to differentiate between two spots
  • In a light microscope, the resolution is roughly 0.2 micrometers
• Living cells and tissues can be viewed under a light microscope, but they are often transparent
• Tissue samples for a light microscope must be very thin to allow light to pass through
• Equipment for measuring structures in a microscope:

  • Slide graticule: lined ruler on a microscope slide
  • Eyepiece ruler: ruler imprinted on the eyepiece lens
• Calibrating measurements:

  • Use the eyepiece ruler to measure in eyepiece units
  • Calibrate using the slide graticule at the same magnification
• Magnification calculations:

  • Magnification = size of the image / actual size of the image
  • Convert measurements to the same scale (e.g., micrometers to nanometers)
• Calculating magnification using a scale bar:

  • Measure the length of the scale bar with a ruler
  • Divide by the actual size of the scale bar to calculate magnification
• Calculating actual size:

  • Actual size = image size / magnification
  • Use the magnification from the scale bar to calculate the actual size of structures in the image
• Electron microscopes use a beam of electrons instead of light and focus the beam using electromagnets, not glass lenses
• Electrons have a much shorter wavelength than light waves, giving electron microscopes a higher resolving power and resolution
• Electron microscopes can see much smaller objects, such as ribosomes, and can see inside cells
• Living samples cannot be viewed with electron microscopes as the whole microscope needs to be in a vacuum
• Electron microscopes are very expensive, large, and time-consuming to prepare samples
• Transmission electron microscopes (TEM) have high resolution but need thin specimens and work on fixed, dead samples