Nucleic Acids: DNA, RNA, and Nucleotides
Nucleic acids are biomolecules made of nucleotide units, where each nucleotide contains a nitrogenous base, a pentose sugar, and a phosphate group.
In one line: Nucleotide has the extra P: base, sugar, phosphate.
Practice This ConceptUnderstand it
- DNA and RNA are polymers of nucleotides.
- A nucleotide has three parts: a nitrogenous base, a sugar, and a phosphate group.
- DNA usually contains deoxyribose sugar and has a double-helical structure with complementary base pairing.
- RNA contains ribose sugar and is generally single-stranded in basic Class 12 treatment.
- DNA stores genetic information, while RNA helps in protein synthesis.
- The flow of genetic information is commonly represented as DNA to RNA to protein.
Example
Rule to remember
Composition rule: nucleoside = nitrogenous base + pentose sugar; nucleotide = nitrogenous base + pentose sugar + phosphate.
Information flow rule: DNA → RNA → protein.
Complementary pairing in DNA is based on specific base pairing.
See it worked out
Follow the example line by line, then use the same method on new questions.
Worked example
Identify the biomolecule unit: 'base + ribose + phosphate' is a nucleotide of RNA because it contains ribose sugar and phosphate along with a base.
Method you can reuse
- 1First check whether phosphate is present.
- 2If absent, write nucleoside; if present, write nucleotide.
- 3Then identify sugar: deoxyribose indicates DNA, ribose indicates RNA.
- 4Finally relate DNA and RNA to information transfer and protein synthesis.
Visual tip
Required diagram showing nucleotide components, DNA double helix idea, and a simple DNA to RNA to protein flow chart.
Check yourself
Answer the question in your head before opening the answer.
Try it yourself
What is the difference between a nucleoside and a nucleotide?
Think first, then show answerHide answer
Common wrong answer
Calling base plus sugar plus phosphate a nucleoside is wrong; phosphate makes it a nucleotide.
Exam tip
Write it in the exam
Each point is worth about one mark. Write point 1 for a 1-mark question and keep adding points as the marks go up.
How CBSE asks it
- 1
Enough for 1 mark
Nucleic acids are biomolecules made of nucleotide units, where each nucleotide contains a nitrogenous base, a pentose sugar, and a phosphate group.
- 2
Add for 2 marks
Example: A DNA nucleotide contains a base such as adenine, deoxyribose sugar, and phosphate group.
- 3
Add for 3 marks
DNA and RNA are polymers of nucleotides.
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