Study GuideMicrobiology–DNA and Gene Expression1.DNA StructureDuring the 1950s, biology experienced rapid scientific growth. Researchers began to understandhowgenes workand how genetic information controls cell activities. These discoveries led to thedevelopment ofmolecular genetics, a field that studiesDNAand explains how it directs theproduction of proteins in microorganisms and other living cells.1.1The Discovery of DNA StructureIn 1953,James Watson and Francis Crickproposed the correct structure of DNA. They showed thatdeoxyribonucleic acid (DNA)is made oftwo long chains of nucleotides.•The two chains twist around each other to form adouble helix.•The structure looks like aspiral staircase.•The two strands are held together byweak hydrogen bondsbetween specific nitrogenousbases.1.2The Building Blocks of DNA: NucleotidesEach DNA strand is made of repeating units callednucleotides.Every nucleotide hasthree parts:1.A nitrogenous base2.A phosphate group3.A sugar molecule called deoxyriboseNitrogenous BasesThere arefour nitrogenous basesin DNA. These bases fall into two categories:Preview Mode
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