Gel electrophoresis

  • separation of strands of DNA of different lengths
  • analysis of proteins and DNA
  • place mixture of molecules into wells cut in agarose gel and apply electric field
  • factors affecting movement speed of molecules:
  • net charge of molecules
  • size of molecule
  • composition of gel: size of ‘pores ‘ within gel


Electrophoresis of proteins

  • separates polypeptides produced by different alleles of many genes
  • charge on protein is dependent on the ionization of the R groups on the amino acid residues
  • charge depends on pH hence use of buffer solution to keep constant pH
  • polypeptides separate due to different net charges
  • proteins are usually negatively charged


Electrophoresis of DNA

  • a region of DNA is chosen
  • DNA is extracted
  • DNA is chopped into pieces using restriction endonucleases
  • fragments are transferred to absorbent paper and placed onto gel; heated to separate DNA strands
  • short sequences of single-stranded DNA are added. They contain radioactive P isotopes; X-ray results, darken film, the separated fragments become visible


Describe how electrophoresis is used in genetic fingerprinting

(Outline how genetic fingerprinting is carried out)

  • ref. to VNTR (sequences) ;
  • quantity of DNA increased by PCR ;
  • DNA fragmented by, restriction enzyme(s) / endonuclease(s) ;
  • loaded (into wells) in agarose gel ;
  • (at) negative end/ cathode end ;
  • ref. to buffer/ electrolyte ;
  • direct current applied ;
  • phosphate groups of DNA give negative charge ;
  • (negatively charged) DNA attracted to, anode/ positive electrode ;
  • short pieces/ smaller mass, move further/move faster ;
  • (pieces) transferred to, membrane/ nylon/nitrocellulose/ absorbent paper or Southern blotting ;
  • heated to separate strands ;
  • probes/ fluorescent dye, added ;
  • X-ray film/ UV light/ lasers ;
  • pattern of stripes/ ref. banding pattern ;


Leave a Reply

Your email address will not be published. Required fields are marked *