Build the partner strand
"Build the partner strand" is a free, interactive Class 12 Chemistry simulation for NEET and JEE, built on the lesson "Nucleic acids" in Biomolecules. The top strand is fixed. Choose a position, then the base that should sit opposite it on the second DNA strand. A green rung means the pair is right; the cursor moves on by itself. DNA: deoxyribose, bases A, G, C, T, two complementary strands with A–T and C–G pairs. RNA: ribose, U instead of T, a single strand. JEE Main asked 50 questions from this chapter across the 42 shifts Lumi has analysed (2017–2026).
From the lesson Nucleic acids in Biomolecules. Change the values and watch what happens.
In JEE Main
42 shifts analysed
50 questions from Biomolecules across the 42 JEE Main shifts Lumi has analysed (2017–2026).
The idea behind it
NCERT §10.5–10.5.3
- Heredity is carried by chromosomes in the cell nucleus, made of proteins and nucleic acids. The two nucleic acids are DNA (deoxyribonucleic acid) and RNA (ribonucleic acid). Both are long chains of nucleotides, so they are also called polynucleotides.
- Complete hydrolysis gives three things: a pentose sugar, phosphoric acid and nitrogen-containing heterocyclic bases. The sugar is β-D-2-deoxyribose in DNA and β-D-ribose in RNA.
- Bases: DNA's four are A (adenine), G (guanine), C (cytosine) and T (thymine). RNA shares A, G and C but carries U (uracil) where DNA has T.
- A nucleoside is a base joined to C1′ of the sugar; the primes keep sugar carbons apart from base atoms. A nucleotide is a nucleoside with phosphoric acid on C5′ of the sugar.
- Nucleotides join through phosphodiester links between the 5′ and 3′ carbons of neighbouring sugars, so the backbone alternates sugar and phosphate with a base on each sugar.
- Primary structure is the sequence of nucleotides. Watson and Crick proposed DNA's secondary structure: two strands wound as a double helix, held by hydrogen bonds between bases.
- Pairing is specific: adenine with thymine, cytosine with guanine. So the two strands are complementary, not identical.
- RNA is a single-stranded helix that sometimes folds back on itself. Its three types are messenger (m-RNA), ribosomal (r-RNA) and transfer (t-RNA).
- DNA is the chemical basis of heredity. It copies itself during cell division so each daughter cell gets identical DNA, and it keeps a species' identity over millions of years. It carries the message for each protein, which the RNAs then build.
- DNA fingerprinting uses the base sequence, unique to a person and the same in every cell: in forensics, for paternity, to identify accident victims by comparing with parents or children, and to study racial groups and evolution.
Questions
3 answers
- What does the "Build the partner strand" simulation show?
- The top strand is fixed. Choose a position, then the base that should sit opposite it on the second DNA strand. A green rung means the pair is right; the cursor moves on by itself.
- Does JEE Main ask questions from Biomolecules?
- Yes. JEE Main asked 50 questions from this chapter across the 42 shifts Lumi has analysed (2017–2026).
- Is this simulation free?
- Yes. It is free and runs in the browser on a phone or a laptop. It belongs to the lesson "Nucleic acids" in Biomolecules (Class 12 Chemistry).
Embed this simulation
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