How does Hershey&Chase and Meselson&Stahl experiments explain DNA criteria:
Can copy itself precisely
Stable that it can be changed
Complex enough to determine phenotype
The Hershey and Chase experiment and the Meselson and Stahl experiment both provide strong evidence for how DNA meets the criteria of being able to copy itself precisely, being stable to allow for changes, and being complex enough to determine phenotype.
The Hershey and Chase experiment demonstrated that DNA is the genetic material that carries the instructions for inheritance. They used a virus (bacteriophage) that infects bacteria and has a protein coat and DNA inside. They labeled the protein coat with radioactive sulfur and the DNA with radioactive phosphorus. When the bacteriophage infected the bacteria, only the radioactive DNA, not the protein coat, was found within the bacteria. This convincingly showed that DNA, not protein, is the genetic material that is passed on to the next generation. This experiment supports the notion that DNA can copy itself precisely because it carries the genetic information necessary for the reproduction of an organism.
The Meselson and Stahl experiment provided strong evidence for the semi-conservative replication of DNA. They used heavy nitrogen isotopes to label the DNA in bacterial cells, and then they switched to a lighter isotope of nitrogen. By analyzing the DNA over several generations, they found that the new DNA consisted of both heavy and light DNA strands, confirming that DNA replicates in a semi-conservative manner. This means that each new DNA molecule formed in replication consists of one strand from the original molecule and one newly synthesized complementary strand. This precise copying mechanism ensures that the genetic information is faithfully preserved and passed on to successive generations.
In terms of stability, DNA has a strong chemical structure that allows it to remain intact over long periods of time. This stability is crucial for the accurate transmission of genetic information from one generation to the next, preventing errors or mutations that could disrupt the functioning of an organism.
DNA is also complex enough to determine phenotype, which refers to the observable characteristics of an organism. The sequence of nucleotides in DNA contains the instructions for the synthesis of proteins, which are key players in determining an organism's phenotype. Proteins are involved in a wide range of processes including cell structure, enzyme activity, and the regulation of gene expression. By carrying the genetic code, DNA encodes the information required for the synthesis of these proteins, ultimately influencing an organism's characteristics.
In summary, the Hershey and Chase experiment and the Meselson and Stahl experiment provide evidence for how DNA meets the criteria of being able to copy itself precisely, being stable to allow for changes, and being complex enough to determine phenotype. These experiments highlight the fundamental properties of DNA that make it the hereditary molecule in all living organisms.