Embed Size (px)
Citation preview
Introduction to Techniques
Restriction Enzymes, PCR and Gel Electrophoresis
• Restriction enzymes are also called restriction endonucleases– They cut double stranded DNA at sequence specific
sites– They can produce “sticky ends” or blunt ends
depending on the enzyme
Sticky Ends
Sticky Ends
Blunt Ends
Blunt Ends
Restriction Enzymes
• 1978 Nobel Prize in Medicine was awarded to Daniel Nathans and Hamilton Smith for the discovery of restriction endonucleases– Restriction enzymes were discovered in E.coli as a
defense mechanism against bacterial viruses (bacteriophages)
• The recognition sites are usually 4-12 nucleotides long– Sequences are palindromic (GAATTC)
• There are hundreds of restriction enzymes currently being used
Restriction Enzymes
• Restriction enzymes are commonly used in laboratories to create recombinant DNA
• Harvest DNA products for other applications
• DNase a general nuclease used to eliminate DNA in RNA samples
Restriction Enzymes: Applications
Restriction EnzymesWhat is better for making recombinant DNA: Sticky ends or blunt ends?
Restriction Enzymes
Restriction Enzymes
• Student activity
• Potential Problems:– Wrong buffer– * activity
• Online resources http://www.dnai.org/b/index.html
• Click on Techniques– Restriction enzymes are found in cutting and
pasting
Restriction Enzymes
Gel Electrophoresis• Gel electrophoresis is used to separate nucleic
acids (DNA and RNA) or proteins for analytical use– DNA and RNA are separated using agarose– Proteins are separated using polyacrylamide– The gel is a matrix (cross-linked polymers) that allow
products to be separated
• Separation is based on the size (not shape) of a product as it moves through a charged field
Gel Electrophoresis• The negative charge is at the top (closest to
the samples) and the positive charge is at the bottom– Samples are negatively charged and will travel
towards the positive charge• DNA and RNA are negative because of their sugar-
phosphate backbone• Proteins are denatured to give a constant shape and
given a charge through the negative loading buffer used
– Samples are diluted in a loading buffer that helps the samples stay in the wells
Gel Electrophoresis
• Applications
– Separating restriction digests
– Analyzing/purifying PCR products
– Sequencing
– Protein analysis
Gel Electrophoresis
Gel Electrophoresis
Gel Electrophoresis
• Sample agarose gel stained with ethidium bromide (EtBr)
Gel Electrophoresis• Student activity
– Practice loading a gel with 20uL Kool Aid or food coloring
– Run gel and see color separation– Discuss what it means for the colors to
separate
Gel Electrophoresis
Gel Electrophoresis
Gel Electrophoresis• Potential Problems
– Connecting the charges backward– Not enough loading dye– Running the gel too hot– Handling EtBr
• Online Resources: http://www.dnai.org/b/index.html
• Click on Techniques– Gel electrophoresis is found in sorting and
sequencing
• Invented in 1983 by Kary Mullis (Nobel Prize in 1993 for its discovery)
• Uses primers to exponentially amplify a specific region of DNA
• Components needed for the reaction:– DNA – Primers to region of interest– DNA polymerase (Taq – used to synthesize the DNA)– dNTPS (the building blocks of the copied DNA) – Buffer (with appropriate salts to ensure the enzyme
works properly)
PCR
• Three steps of the reaction:– Denaturation: High heat (94-98o) to separate the
strands of DNA– Annealing: (50-60o – depends on the primers) this
step allows the primers to bind to the denatured DNA strands
– Elongation (74o) – DNA polymerase synthesizes the new strand
• This step is dependant on the length of the product to be amplified (1min/1kb of DNA)
• Check products with gel electrophoresis and sequencing
PCR
PCR: Cycles
PCR:
PCR: Thermocycler
• Used to test for gene products for disease diagnosis
• Used to amplify small amounts of material– Forensics– Fossil Records
• Used for recombinant DNA technology
• Used for virus detection
PCR: Applications
• Potential Problems– No amplification due to wrong buffer
conditions – No amplification due to lost enzyme activity– Primers are wrong
• Online Resources: http://www.dnai.org/b/index.html
• Click on Techniques– PCR is found in amplifying
Resources
