Collection of techniques to study dna structure and function. *cleavage of dna at specific sites enzymes - restriction nucleases. *dna sequencing by gel electrophoresis analysis of dna base sequences. *nucleic acid hybridization based on complementary base pairing uses labeled dna or rna to locate genes on dna. *dna cloning copying of dna sequences polymerase chain reaction. *dna engineering modification of dna sequences insertion into cellular dna. Cell culture - source of homogenous cells for studying genes, proteins, molecular mechanisms, etc. Cells can be isolated from tissues and grown in culture. *differentiated cells: maintain properties characteristic for cell type, have finite life time in culture, can be immortalized and propagated for long time in culture. *undifferentiated cells: can divide and grow indefinitely in culture, can be stimulated to differentiate to a different cell types. *malignant tumor cells: can be propagated indefinitely in culture. *bacterial enzymes that cut (hydrolyze) dna at specific sequences of 4-8 nucleotides (restriction site)