Introductory Biology

9.1 Identifying the Genetic Materials

Chromosomes are made up DNA and protein. For 50 years, scientists wondered if it was DNA or protein that passed on information. *DNA is made up of 4 different nucleotides. *Proteins are made up of 20 amino acids. Since proteins had more letters, the scientists thought that proteins passed on the information.

DIscovery of DNA: DNA was found when people looked at the nucleus of cells when they found that there are two molecules in the one test tube.120 years ago they found nucleic acids.  Scientists knew about proteins and how they made muscles and soon found that the other solution contains phosphorus.

Another experiment was by Friedrich Miescher who looked at what was in the garbage can of local hospitals to collect bandages. He added alkaline solutions to the salt solutions and found “nuclein” (aka nucleic acid).
In the early 1900s, Phoebus Levene decided to look at DNA. A typical protein has a number of possibilities and has different molecules you can put at each position. So, proteins come in various shapes and sizes. The molecule Phoebus worked on only had four nucleotides. Found that a nucleotide is made up of three elements: phosphate, deoxyribose sugar, and nitrogen-containing base. There are four possible letters and the nucleotides link to each other from sugar to phosphate.
Griffith and Avery Helped Identify DNA as the Genetic Material.Fred Griffiths found that in his hospital there were bacteria and experimented what made them deadly. The smooth variety was tested by injecting the bacteria on the mouse, and it died. A different strain of the same bacteria was tested onto the mouse, the mouse didn’t die. S-strain bacteria (virulent=disease causing), have a protective capsule, and are deadly. R-strain bacteria are NOT deadly because they lack capsules. Heat-killed S strain bacteria do NOT kill mice. But the heat-killed S-strain + R-strain kill mice. The bacteria growing inside the dead mice had been transformed into S-strain bacteria. Conclusion of Griffith’s experiments (Streptococcus pneumoniae): the S-strain bacteria has a capsule and is deadly (is a smooth cell because it has a capsule). The S-strain has the capsule because it has the gene to make the protein to make the capsule. The R-strain bacteria does not have a capsule and is harmless. Heat-killed S-strain are harmless. The heat-killed S-strain and R-strain kill the mice and when you take some of their blood its S-strain bacteria. One genetic material had been transforming the R-strain so tested all protein, carbohydrate, RNA, and DNA to see which material is the transforming principle.
protein + R-strain = no change
carbohydrate + R-strain = no change
RNA + R-strain =
DNA + R-strain = change
** ONLY DNA was able to change the solution
Protein is not the genetic material.
** Transformation: picking up the gene from the environment.
Add enzymes (speed up action) to get rid of the protein. Avery’s experiment was to determine the transforming molecule is DNA. The transformation was not affected by protein-destroying enzymes, therefore the genetic material is not protein. But the transformation was stopped by DNA-destroying enzymes, therefore the genetic material is DNA.

Hershey and Chase Show that Virus Genes are Made of DNA by using phage. Viruses multiply in your cells. Viruses are just made out of DNA and protein and only of two parts. Radio active materials are great for following things. Take a virus and we notice that protein has a element that DNA lacks = Sulfur. DNA has phosphorus and virus doesn’t. A coat remains outside and the genetic material is injected into the host so the viruses are great to show that DNA is the genetic material and not protein.

Phage viruses: The proteins stay outside

Radioactive sulfur in the protein are allowed to infect the bacteria, then put on the blender so the coats are separated from the bacteria = the radioactive sulfur stays on the light and outside so PROTEIN IS NOT THE GENETIC MATERIAL. Viruses with radioactive sulfur (part of protein) infect bacterias and so the protein always remains outside which show  that the coat is made of protein. Radioactivity is only in the DNA, not proteins.Viruses with radioactive phosphorus (part of DNA) infect bacterias and the radioactive phosphorus always goes inside the cell, so the genetic material is DNA.This experiment showed that the genetic material is DNA.


One thought on “9.1 Identifying the Genetic Materials

  1. Yurika,

    You’ve written an excellent entry for 9.1 on the discovery that DNA is the genetic material. You’ve captured a high level of detail about the two experiments, and organized the information well. Great job!

    Mr. F.

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