Experiment 12: UV Light Mutations

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Experiment 12 UV Light Mutations

• UV light is known to cause skin cancer
• UV light can kill it is sometimes used to
  sterilize surgical instruments
• What happens at the level of DNA?

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DNA mutations due to Ultraviolet light Thymine
Dimers

• Bonding of adjacent thymine distorts DNA
  molecule.
• DNA Repair Enzymes can correct this problem
• a UV enzyme removes Thymine dimer a few
  nucleotides to either side.
• DNA polymerase brings in correct replacement
  nucleotides.
• DNA ligase seals nicks in sugar phosphate
  backbone.

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What Happens When Genes for DNA repair enzymes
contain mutations?

• Other mutations go uncorrected!
• Xeroderma Pigmentosum (XP)
• Autsomosal recessive
• Function affected individual lacks proper
  version of an enyme needed to repair UV damage
  to DNA.
• Symptoms Sunlight brings on pigmented spots
  cancercous growths. Usually results in early
  death due to skin cancer.

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Effect of UV light on the growth of Bacteria

• Exposing bacteria to UV light is expected to
  affect their growth. How?
• Inoculate petri dishes with bacterial culture
• Expose petri dishes to UV light for different
  amounts of time
• Look at results next week

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Expt. 13 DNA Extraction

• Detergent dissolves the plasma membrane
• Washing dishes with detergent
• Heat block for 15 min helps the process
• Washing dishes with detergent in warm water
• Meat tenderizer contains enzymes that degrade
  protein. Heat block for additional 10 min.
• Add COLD alcohol
• Precipitates the DNA
• Look for DNA at the interphase

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Expt. 14 Stages of Mitosis

• Interphase G1-S-G2
• Normal functions
• Prophase
• nuclear envelope degrades,
• chromosomes condense
• spindle forms from the centrioles
• Metaphase
• Chromosomes attach to the spindle at the middle
  of the cell
• Anaphase
• Chromatids separate at centromeres
• Chromosomes move to poles
• Telophase
• Nuclear envelope reforms in each of two daughter
  cells
• Cytokinesis separates two new cells

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Onion Root Structure
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