EasyBiologyHigh School (11–12)Heredity and Evolution › Molecular Basis of InheritanceConceptualAPA-LevelIB
A student plans an experiment like that of Hershey and Chase…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A student plans an experiment like that of Hershey and Chase. The choices for a radioactive tag are carbon-14, hydrogen-3 (tritium), phosphorus-32 and sulphur-35.
- Which tag follows the DNA of a phage and not its protein?
- Which tag follows the protein and not the DNA?
- Why would carbon-14 not tell the two molecules apart?
- In which part of a spun tube is the DNA tag found after the bacteria are infected, blended and spun?
Need a reminder? The key ideaShow
Griffith found that heat-killed S cells change live R cells into S cells. Avery, MacLeod and McCarty found that only DNase stops this change. Hershey and Chase tagged DNA with 32P and protein with 35S. The 32P went into the bacteria, and the 35S stayed outside.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. (a) DNA has phosphate groups, and its tag is phosphorus-32. Protein has no phosphorus in its coat.
Step 2. (b) Protein has sulphur in the amino acids cysteine and methionine, and DNA has none. So the tag for protein is sulphur-35.
Step 3. (c) Carbon (and hydrogen) are in both DNA and protein. A tag of carbon would mark both, and the experiment could not tell which one entered the cell.
Step 4. (d) The DNA goes into the bacteria, and the bacteria form the heavy pellet. The tag is in the pellet.
Answer: (a) 32P; (b) 35S; (c) carbon is in both molecules; (d) the pellet.
Discussion (0)
Log in to join the discussion.
Loading…