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DNA nucleotides form hydrogen bonds with other nucleotides. Which complementary base pairs form?

• Adenine and thymine form 2 hydrogen bonds.

• Adenine and cytosine form 2 hydrogen bonds.

• Adenine and guanine form 3 hydrogen bonds.

• Adenine and thymine form 3 hydrogen bonds.

Purine bases always pair with other purine bases, and pyrimidines with other pyrimidines.

• True

• False

DNA is made of two strands running anti-parallel. What is at the 3' end?

• A phosphate group attached to carbon 3 of the pentose.

• An OH attached to carbon 3 of the pentose.

• A nitrogenous base attached to carbon 3 of the pentose.

What is the purpose of adding salt during DNA extraction in a laboratory?

• To break down the cell membrane.

• To break the hydrogen bonds between DNA and water molecules.

• To break down the proteins (histones) associated with DNA.

• To cause the DNA to precipitate out of solution.

What is the purpose of adding ethanol during DNA extraction in a laboratory?

• To break down the cell membrane.

• To break the hydrogen bonds between DNA and water molecules.

• To break down the proteins (histones) associated with DNA.

• To cause the DNA to precipitate out of solution.

Which are pyrimidines?

• Adenine

• Cytosine

• Guanine

• Thymine

• Uracil