研究生分子生物学概论.pptVIP

Analytical Tools Physical-chemical analysis has often used: Ultracentrifugation Used to estimate size of material Electrophoresis Indicated high charge-to-mass ratio Ultraviolet Absorption Spectrophotometry Absorbance of UV light matched that of DNA Elementary Chemical Analysis Nitrogen-to-phosphorus ratio of 1.67, not found in protein Gel Electrophoresis This technology allows scientists to identify DNA! Steps Involved in Gel Electrophoresis 1. “Cut” DNA sample with restriction enzymes. 2. Run the DNA fragments through a gel. 3. Bands will form in the gel. 4. DNA bands are unique and can be used to identify a species. 5. DNA bands are like “genetic fingerprints”. DNA: The Transforming Material In 1944 a group used a transformation test, defined---- the chemical nature of the transforming substance Techniques used excluded both protein and RNA as the chemical agent of transformation verified that DNA is the chemical agent of transformation Procedure for the Hershey-Chase Transformation Experiments DNA Structure Rosalind Franklin’s x-ray data suggested that DNA had a helical shape; The data also indicated a regular, repeating structure DNA was believed to require an irregular sequence Watson and Crick proposed a double helix with sugar-phosphate backbones on the outside and bases aligned to the interior DNA Helix Structure compared to a twisted ladder Curving sides of the ladder represent the sugar-phosphate backbone Ladder rungs are the base pairs There are about 10 base pairs per turn Arrows indicate that the two strands are antiparallel Components of DNA Biochemists determined the components of nucleotides during the 1940s The component parts of DNA Nitrogenous bases: Adenine (A) Cytosine (C) Guanine (G) Thymine (T) Phosphoric acid Deoxyribose sugar Components of DNA The DNA molecule is a double helix, with sugar-phosphate backbones on the outside and base pairs on the inside The bases pair in a specific way: Adenine (A) with thymine (T) Guanine