Question

1. You are working in a laboratory where you are investigating pieces of an asteroid that have been brought to earth. You are taking every safety precaution (hazmat suit etc…) as it is thought that the asteroid pieces contain bacteria-like microorganisms from another planet.

1. Indeed, when you look under the microscope at the pieces of rock you see tiny bacteria-like microorganisms. These microbes double in number every few hours when you culture them in a liquid broth. You decide to see if the microbes might be toxic to mammals on earth and you inject the alien microbes into mice. The mice die!

1. You determine that these microbes have surprising biochemical similarities to microbes on earth; they have nucleic acids, proteins, lipids and carbohydrates. However, their nucleic acids are slightly different. They have a molecule similar to DNA, but the five carbon sugar has a 2’-OH group and not a 3’-OH group (the RNA-like molecule has both a 2’-OH as well as a 3’-OH, similar to what is found on earth, but nucleotides connect to other RNA nucleotides via the 2’-OH not the 3’-OH). Additionally, the nitrogenous bases of the alien nucleic acids are purine-like (two of them) and pyrimidine-like (two of them) and have the same chemical structure as A, C, G and T, but because of the difference in how nucleotides connect, you call the bases H, I, J and K. You wish to determine the pairing of the H, I, J and K nucleotides of the alien pairs. For example on earth you know that G pairs with C, and that A pairs with T. You want to know the same for your organism and you are inspired by Chargaff. Describe how you could use Chargaff’s approach to determine which bases pair with each other. Describes results that would be ones that could allow you to make a conclusion about base pairing in the alien microbe. (10 points)

1. You next wish to determine if the alien microbes are similar enough to earth microbes to be capable of transforming non-virulent earth microbes with the genetic material of the virulent strain of the alien microbe. How would you conduct this experiment? Describe the experimental setup and results that would indicate that the chemical constituents of the alien microbes were capable of transforming non-virulent earth microbes into a virulent form of microbe. Be sure to include appropriate controls. (15 points)

1. You next wish to determine what biochemical constituent of the alien microbe is responsible for the transformation of the earth microbes. You hypothesize that it is either the alien “DNA” or the alien “RNA” or the alien protein. Describe the setup of an experiment that you could conduct to determine which one of the three molecules is responsible for the transformation. (15 points)

1. Next, you are surprised that the molecule responsible for the transformation is not the alien DNA but rather it is the alien RNA. What would the results be of your experiment (described in iii above) that would indicate that it was the RNA of the alien microbe that was responsible for the transformation of the normal earth bacteria? (10 points)

2. You find that the RNA-like molecule also serves as the genome of the alien microbe and that it undergoes conservative replication in the alien microbe. Describe the experiment you would do to show this using density gradient centrifugation and using ¹⁵N. (10 points)

Answer 1

according to Chargaff and his colleagues four nucleotide bases of DNA of a different organism that the amount of certain base is closely related.

they give four conclusions for base pairing

1. every species vary from each other on the basis of the base composition of DNA.

2. in the organism every tissue has the same DNA.

3. The base composition of DNA in a given species does not change with an organism's age, nutritional state, or changing environment.

4. in cellular DNA, adenosine residues is equal to the number of thymidine residues and the number of guanosine residue is equal to the number cytidine residue.

according to Griffith's experiment, avirulent microbes convert to virulent. in his experiment virulent microbes like (pneumonia-causing organism) injected into the mice then mice die. again virulent kill by heat and injected into the mice and survive. avirulent microbes inject into the mice again mice survive. heat-killed virulent microbes and avirulent microbes both injected into the mice then it dies. it proofs that avirulent microbes converted into virulent.

according to O.T Avery, Coline Macleod Maclyn McCarty infected sample taken digest with DNAse and found that DNA is degraded and again treated with RNAse and found that RNA is degraded and protein is treated with proteases and protein is degraded. first treated with DNAase and found no transformation then it proofs that which transfer that is DNA.