Chemistry · Biomolecules · NEET
A nucleoside has only two parts: a nitrogen base joined to a pentose sugar (base + sugar). A nucleotide has three parts: base + sugar + phosphate. So a nucleotide is simply a nucleoside with a phosphate group added. The phosphate is the one and only extra part. For NEET, remember the build-up order: base + sugar makes a nucleoside, then + phosphate makes a nucleotide.
The nucleoTide has the phosphaTe. A nucleoside has NO phosphate. This is the most common confusion in NEET. Use the T-hook: nucleoTide and phosphaTe both contain the letter T, so the nucleotide is the one carrying the phosphate.
The nitrogen base attaches to the 1' (one-prime) carbon of the pentose sugar to form the nucleoside. The phosphate group attaches at the 5' (five-prime) carbon of that same sugar to form the nucleotide. NEET has asked this exact detail: base at 1', phosphate at 5'.
It is phosphoric acid (H3PO4), NOT phosphorous acid (H3PO3). This is a favourite NEET trap. In NEET 2023 a statement said the nucleotide forms with 'phosphorous acid' - that statement was marked FALSE. The nucleoside reacts with phosphoric acid (H3PO4) at the 5' position to give the nucleotide.
DNA and RNA are polymers of nucleotides (they must have the phosphate, because the phosphate forms the linkage that joins one sugar to the next). The repeating unit of a nucleic acid is a nucleotide, not a nucleoside. Examples of nucleotides: AMP, ADP, ATP - all have adenine base + ribose sugar + phosphate.
Nucleosides (base + sugar, no phosphate): adenosine, guanosine, cytidine, uridine, thymidine. Nucleotides (base + sugar + phosphate): adenylic acid (AMP), and the energy molecule ATP. Notice ATP has three phosphates, but even one phosphate already makes it a nucleotide.
Given below are two statements. Statement I: A unit formed by the attachment of a base to the 1' position of sugar is known as a nucleoside. Statement II: When a nucleoside is linked to phosphorous acid at the 5'-position of the sugar moiety, we get a nucleotide. In the light of the above statements, choose the correct answer.
The correct statement regarding RNA and DNA, respectively, is:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
A nucleotide is bigger because it has one extra part - the phosphate group. Nucleoside = base + sugar (2 parts). Nucleotide = base + sugar + phosphate (3 parts).
The nucleotide is the repeating (building-block) unit of both DNA and RNA. The phosphate is needed to link the units together, so nucleic acids are polymers of nucleotides.
ATP (adenosine triphosphate) is a nucleotide because it contains phosphate groups (three of them) along with the adenine base and ribose sugar. Its no-phosphate version, adenosine, is the nucleoside.
The nitrogen base joins at the 1' carbon of the sugar, and the phosphate joins at the 5' carbon of the sugar. Base at 1', phosphate at 5' - NEET has asked this exact point.
Phosphoric acid, H3PO4. Not phosphorous acid (H3PO3). NEET 2023 used this swap to make a false statement, so always check the spelling.
