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Lab 5: DNA and ChromosomesBIOL107, San Diego Mesa CollegeObjectives●Describe the structure and function of DNA.●Describe the characteristics of and visually identify homologous chromosomes●Describe the expected chromosomal content of human cells and explain howchromosomal abnormalities lead to genetic disorders.●Explain how alleles, chromosomes, and other factors determine sex in animals●Explain how to conduct karyotype analysis and interpret the results.Exercise 5.1 The Genetic Content of CellsDNA Stores the Genetic Information of the CellDNA, deoxyribonucleic acid, is the hereditary molecule in living organisms; it’s whatmakes you! This molecule stores information about how to assemble the many types of proteinsneeded to build cells and support their functions. This information is found in the sequence ofmonomers callednucleotides. A nucleotide contains three subunits: a 5-carbon sugar calleddeoxyribose, a phosphate group, and one of four differentnitrogenous bases;adenine,thymine, cytosine, and guanine (Figure 5.1). Nucleotides are joined together to form a polymer,orpolynucleotide. DNA has twolong polynucleotide strands thatcome together by hydrogen bondsbetween the nitrogenous bases;however, not just any nitrogenousbase can join to another, onlycomplementarybases can. Thecomplementary bases areadenine and thymine, and alsocytosine and guanine; theirstructure is what allows them tobond to each other. Finally, theentire double-stranded moleculethen twists upon itself forming ahelical structure, the double helix(Figure 5.2)!Figure 5.2 DNA Structure. (a) TheDNA double helix, (b) SimplifiedDNA structure showingcomplementary base-pairingbetween nitrogenous bases, and1Figure 5.1. Nucleotide Structure
(c) Complex molecular structure of DNA, showing sugar-phosphate backbone andcomplementary base pairing.