Manipulating DNA

Scientists use their knowledge of the structure of DNA and its chemical properties to study and change DNA molecules Different techniques are used to study and change DNA molecules

Tools of Molecular Biology Genetic Engineering – making changes in the DNA code of a living organism DNA extraction Cells opened to separate DNA from other cell parts Cutting DNA –DNA too large to study, so biologists “cut” them into smaller fragments using restriction enzymes. Many restriction enzymes are known and each one cuts DNA at a specific sequence of nucleotides

Restriction Enzymes Recognition sequences DNA sequence Restriction enzyme EcoR I cuts the DNA into fragments. Sticky end

Restriction Enzymes Recognition sequences DNA sequence Restriction enzyme EcoR I cuts the DNA into fragments. Sticky end

Separating DNA Gel electrophoresis –Used to separate DNA fragments. DNA fragments placed in a gel and electricity is applied to the gel. DNA molecules are negatively charged and move towards the positive end of the gel. Smaller DNA fragments move faster and farther –This technique used to compare the genomes of different organisms or even different people

Gel Electrophoresis DNA plus restriction enzyme Mixture of DNA fragments Gel Power source Longer fragments Shorter fragments

Gel Electrophoresis

DNA from Victim DNA from Suspect #1 DNA from Suspect #2 DNA from Suspect #3 DNA from Suspect #4 Blood found at Crime Scene Which suspect should have more questioning?

Using the DNA Sequence Knowing the DNA sequence, we can study and compare specific genes Reading the Sequence –Small, single-stranded pieces of DNA placed in test tubes with an enzyme that can make a complementary strand of DNA –A supply of the 4 bases (A, T, G, C) is added, along with specific colors for each base which attach to the DNA strands –Tiny, color-coded DNA fragments separated by gel electrophoresis. Color pattern gives sequence of bases in DNA

DNA Sequencing Fluorescent dye Single strand of DNA Strand broken after A Strand broken after C Strand broken after G Strand broken after T Power source Gel

Cutting and Pasting DNA DNA sequences can be changed by splicing original DNA with “synthetic” pieces from another organism Splicing – adding in a new section of DNA into an existing piece of DNA Recombinant DNA – combining DNA from different sources –Ex. Taking E. coli and inserting the human gene for making insulin into the bacteria’s DNA so that it produces human insulin for diabetics

Making Copies of DNA Polymerase Chain Reaction (PCR) technique –Allows biologists to make many copies of DNA –DNA strands separated with heat, then cooled to allow DNA Polymerase to start making new copies of DNA –A few dozen heat and cool cycles results in many copies of DNA

Making Copies of DNA DNA polymerase adds complementary strand DNA heated to separate strands DNA fragment to be copied PCR cycles 1 DNA copies etc. 16 etc.