If Cells Are Provided with Nucleotides Labeled with a Radioactive

question 53

Multiple Choice

If cells are provided with nucleotides labeled with a radioactive isotope of hydrogen (³H) ,newly synthesized DNA will be radioactively labeled.In a set of experiments,a student-faculty research team introduced labeled T nucleotides into cultures of dividing human lymphocytes at specific times.A pathogen was introduced into one culture prior to the start of the experiment,and another culture was left untreated as a control.Following a 24-hour incubation with the radiolabeled nucleotides,cells were lysed,and the DNA was isolated and tested for presence of radioactivity.The research team found that lymphocytes exposed to a pathogen incorporated three times the amount of labeled nucleotide as the control.Which of the following hypotheses might explain these observations?

• A)The pathogen thrived in culture and incorporated the excess nucleotide.
• B)Infection causes lymphocyte cultures to skip some parts of the cell cycle.
• C)Infection causes lymphocytes to reproduce more rapidly.
• D)Infection causes cell cultures in general to reproduce more rapidly.