8. explain how the following experiment provided support for the claim that dna is the primary source of heritable information.

two experiments are run side by side:

1. one set of virus particles is labeled with the sulfur-35 isotope. a second set is labeled with phosphorus-32 isotope.

2. each set of labeled virus particles is incubated with different batches of the same bacteria.

3. following infection of the bacteria by the virus particles, the bacteria are separated from the virus particles by agitation in a blender.

4. the bacterial cells are separated from the virus particles by centrifugation.

5. the supernatant and pellet (two separated components) from each batch are analyzed to determine the locations of the isotope labels.

results:

1. radioactive sulfur is found in the supernatant.

2. radioactive phosphorus is found in the cell pellet.

3. a new generation of viable virus particles emerge from the bacteria cells when they are reconstituted in liquid culture.

step 1: initiation

initiation is the beginning of transcription. it occurs when the enzyme rna polymerase binds to a region of a gene called the promoter. this signals the dna to unwind so the enzyme can ‘‘read’’ the bases in one of the dna strands. the enzyme is now ready to make a strand of mrna with a complementary sequence of bases.

step 2: elongation

elongation is the addition of nucleotides to the mrna strand. rna polymerase reads the unwound dna strand and builds the mrna molecule, using complementary base pairs. there is a brief time during this process when the newly formed rna is bound to the unwound dna. during this process, an adenine (a) in the dna binds to an uracil (u) in the rna.

step 3: termination

termination is the ending of transcription, and occurs when rna polymerase crosses a stop (termination) sequence in the gene. the mrna strand is complete, and it detaches from dna.

in the year 2850, humans successfully colonized mars. the martian modules that were constructed could hold only a small population of people. it is now a century later, and the population on mars has grown to 600 people. of the current mars population, 45 people express the recessive phenotype for phenylketon- uria (pku) syndrome (pp genotype).

explanation: