Practice Problems

Working with stock solutions

DNA mass amounts versus concentrations

Generally DNA is stored and used in solution – but when setting up reactions we are told the DNA mass amounts needed – not volumes. For example, a reaction might ask for 5 µg of DNA and your DNA is in a solution at 2 µg/µl. You need to calculate how many µl of your DNA solution to add to the reaction. Here are some practice problems.

Number of molecules versus mass

Beginning molecular biologists have a hard time with the concept of equal numbers of molecules versus equal mass.
The average molecular weight of a DNA base pair is 660 g/mole. Obviously the longer the DNA molecule, the bigger its molecular weight. For some reactions, such as ligations, it is the number of DNA molecules that is important (sometimes we say number of DNA ends) not the actual concentration or mass of the DNA.

Using plasmid maps

Use these plasmid maps

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