Final answer:
A nucleoside consists of a pentose sugar and a nitrogenous base without a phosphate group. Both option 2) adenine + deoxyribose and option 5) adenosine correctly represent nucleosides.
Step-by-step explanation:
The question asks which of the provided options is a nucleoside. A nucleoside is made up of a pentose sugar (which can be either ribose or deoxyribose) and a nitrogenous base (such as adenine, guanine, cytosine, thymine, or uracil). It does not include a phosphate group. Nucleosides can be part of a nucleotide, which is the building block of nucleic acids like DNA and RNA when a phosphate group is added.
Looking at the choices:
- Phosphate + ribose - This is not a nucleoside because it includes a phosphate group.
- Adenine + deoxyribose - This is a nucleoside, specifically a deoxyribonucleoside because it contains a nitrogenous base (adenine) and a pentose sugar (deoxyribose) without a phosphate group.
- Ribose + nitrogenous base - This could be a nucleoside if the nitrogenous base was specified.
- Adenine + ribose + phosphate - This is a nucleotide, not a nucleoside because it includes a phosphate group.
- Adenosine - This is indeed a nucleoside, consisting of adenine (a nitrogenous base) attached to a ribose sugar.
Therefore, both option 2) adenine + deoxyribose and option 5) adenosine are correct answers since each forms a nucleoside.