Lab Quiz 3 - BIOL 402

• Electrophoresis


  A technique that utilizes an electric field to separate different sized DNA fragments
• DNA

  An organic acid (owing to its phosphate groups) and is negatively charged
• Gel electrophoresis

  1. DNA molecules are attracted to the positive pole (the anode) and repelled from the negative pole (the cathode)

  2. Shorter fragments will be able to migrate through the gel more quickly than larger fragments

  3. Fragments of identical size will move at about the same rate in a band
• Agarose gels

  • A lower concentration will produce a loose gel that separates large fragments, while a higher concentration produces a stiffer gel that can separate smaller fragments
  • Produced by pouring a molten agarose solution into a casting tray with a plastic comb suspended, which hardens into a Jell-O-like substance
• Electrophoresis procedure

  1. The solidified gel is immersed in a buffer solution

  2. The comb is removed to produce a series of wells into which the DNA is loaded

  3. The current is turned on, and the negatively charged DNA fragments migrate into the gel toward the anode
• Staining of electrophoresis gels

  • Can be done with a chemical called ethidium bromide, which fluoresces when placed under UV light
  • Can also be done with a non-carcinogenic alternative method called SmartGlowTM, where the SmartGlow loading stain is added directly to the DNA samples and will fluoresce when viewed over a blue light illuminator
• Relative distances moved by the DNA bands

  Indicate the relative sizes of the fragments
• If DNA fragments of known sizes are also run parallel to the unknown sample, the sizes of the unknown fragments can be determined
• DNA

  DNA molecule have a (-) charge on the phosphate group
• (-) charged DNA fragments will move through a gel in an electric field

  anions are attracted to the (+) anode
• smaller DNA fragments move faster through the gel so will be seperated from larger fragments
• How can you tell what fragment has the most DNA?

  By how much it glows.

  The brightest fragment = highest DNA
• non sex-linked ratio

  1:1:1:1
• sex-linked ratio


  2:1:1:0
• white fish blastulla: interphase


  animal

  
• white fish blastulla: metaphase


  animal

  
• allium root tip: interphase


  plant

  
• allium root tip: prophase

  plant

  
• allium root tip: metaphase

  plant

  
• allium root tip: anaphase


  plant

  
• allium root tip: telophase


  plant

  
• Chromatin


  Complex of DNA and proteins (mainly histones) in the nucleus of a cell
• Chromatin


  • In non-dividing cells, it is less condensed, allowing gene expression
  • During cell division, it condenses to form chromosomes
• Chromosome


  Structures formed when chromatin condenses during cell division
• In humans, there are 46 chromosomes, arranged in 23 pairs
• Sister Chromatids


  Two identical copies of a chromosome connected by a centromere
• Formation of Sister Chromatids


  Chromosome replicates its DNA before cell division
• Sister Chromatids


  • During mitosis, they are separated into two new cells, ensuring each new cell gets a complete set of genetic information
• Centromere


  Region where sister chromatids are joined together
• Centromere


  • It serves as the attachment point for spindle fibers, allowing the chromatids to be pulled apart
• Kinetochore


  Protein structure on the centromere of each chromosome
• Kinetochore


  • It connects the chromosome to the spindle fibers during cell division, allowing the chromatids to be separated and moved to opposite ends of the cell
• Spindle Fibers


  Structures made of microtubules that emerge from the centrioles
• Spindle Fibers


  • They form the mitotic spindle, which is essential for separating chromosomes during cell division
  • They attach to kinetochores and help pull sister chromatids apart
• Centrioles


  Cylindrical organelles found in animal cells, part of the centrosome
• Centrioles


  • They play a critical role in organizing spindle fibers during cell division
• Asters


  Star-like structures formed by microtubules that radiate from the centrioles during cell division
• Asters


  • They help anchor the spindle apparatus and ensure proper cell division
• Cleavage Furrow


  Groove that forms in animal cells during cytokinesis (the final stage of cell division)
• Cleavage Furrow


  • It indicates where the cell will split into two new cells, caused by a contractile ring of actin filaments