Nucleosides

What is a nucleoside?

• A nitrogenous base (A, T, C, G, or U)

• a 5-carbon sugar (either ribose or deoxyribose)

• no phosphate group

What is the difference between a nucleoside and a nucleotide?

nucleoside: has a base and sugar

nucleotide: has a base, sugar, and phosphate

What sugar is in DNA nucleosides?

Deoxyribose.

What sugar is in RNA nucleosides?

Ribose.

How are nucleosides named?

RNA nucleosides end in -osine (for purines) or -idine (for pyrimidines)

• Adenosine = adenine + ribose

• Cytidine = cytosine + ribose.

What are the four main RNA nucleosides?

Adenosine, Cytidine, Guanosine, Uridine.

What are the four main DNA nucleosides?

Deoxyadenosine, Deoxycytidine, Deoxyguanosine, Deoxythymidine.

What type of bond connects the base to the sugar in a nucleoside?

• β-N-glycosidic bond

  • between the base and carbon 1′ of the sugar.

Why are nucleosides important?

• once a phosphate group is added, they become nucleotides that can form DNA or RNA.

How can nucleosides be used in medicine?

• Modified nucleosides: used as antiviral or anticancer drugs

• eg. Cytarabine for leukemia

What is the difference between adenosine and deoxyadenosine?

• Adenosine: has ribose (RNA)

• Deoxyadenosine: has deoxyribose (DNA)

  • missing an –OH at the 2′ position.

Which nucleoside contains uracil?

Uridine (uracil + ribose).