DNA Double Helix — Interactive NEET Biology Visual Lab
DNA is a right-handed double helix: two antiparallel sugar–phosphate strands form the outer rails, while the nitrogenous bases project inward and pair as the rungs — adenine with thymine (2 hydrogen bonds) and guanine with cytosine (3 hydrogen bonds). Tap any concept in the interactive model below to explore it, in plain English and with an exam-accurate NEET note.
Explore the DNA helix — tap any part
Tap a structure to see what it does in plain English plus an exam-accurate NEET note, or hit Guided tour to be walked through it step by step.
DNA Helix
Molecular biology
Selected structure
DNA Helix
DNA is the instruction manual inside every cell. It looks like a twisted ladder — a 'double helix'. The outer rails are the sugar–phosphate backbone; the rungs are pairs of chemical letters (A, T, G, C) projecting inward that spell out your genes. Tap a concept, or take the guided tour.
NEET note
▸ All structures & functions
- Double Helix
- DNA is shaped like a twisted ladder — two strands wound around each other.
- NEET:Two antiparallel strands coil into a right-handed double helix (Watson–Crick model).
- Sugar–Phosphate Backbone
- The two outer side-rails of the ladder, made of sugar and phosphate, that hold the strands together.
- NEET:Sugar–phosphate backbone forms the outer rails; the two strands run antiparallel (5'→3' and 3'→5').
- Nitrogenous Bases
- The 'letters' of the genetic code — A, T, G and C — that project inward from the rails to form the rungs.
- NEET:Nitrogenous bases point inward and pair up as the rungs: purines (A, G) and pyrimidines (T, C).
- A–T Base Pair
- Adenine always pairs with Thymine — like two puzzle pieces that only fit each other.
- NEET:Adenine pairs with Thymine via 2 hydrogen bonds (complementary base pairing).
- G–C Base Pair
- Guanine always pairs with Cytosine, held together a little more tightly.
- NEET:Guanine pairs with Cytosine via 3 hydrogen bonds — stronger than A–T.
- Hydrogen Bonds
- Weak 'rungs' in the middle hold the two bases together — weak enough to unzip when DNA is copied.
- NEET:Hydrogen bonds between complementary bases: 2 for A–T, 3 for G–C.
DNA Helix: structures & functions
A quick, exam-focused reference for every structure in the DNA helix — each with a plain-English answer and the precise NEET point.
What is the DNA double helix?
DNA is shaped like a twisted ladder — two strands wound around each other. Two antiparallel strands coil into a right-handed double helix (Watson–Crick model).
What is the sugar–phosphate backbone?
The two outer side-rails of the ladder, made of sugar and phosphate, that hold the strands together. Sugar–phosphate backbone forms the outer rails; the two strands run antiparallel (5'→3' and 3'→5').
What are nitrogenous bases?
The 'letters' of the genetic code — A, T, G and C — that project inward from the rails to form the rungs. Nitrogenous bases point inward and pair up as the rungs: purines (A, G) and pyrimidines (T, C).
What is an A–T base pair?
Adenine always pairs with Thymine — like two puzzle pieces that only fit each other. Adenine pairs with Thymine via 2 hydrogen bonds (complementary base pairing).
What is a G–C base pair?
Guanine always pairs with Cytosine, held together a little more tightly. Guanine pairs with Cytosine via 3 hydrogen bonds — stronger than A–T.
What are hydrogen bonds?
Weak 'rungs' in the middle hold the two bases together — weak enough to unzip when DNA is copied. Hydrogen bonds between complementary bases: 2 for A–T, 3 for G–C.
Frequently asked questions
What is the DNA double helix?
DNA is shaped like a twisted ladder — two strands wound around each other. Two antiparallel strands coil into a right-handed double helix (Watson–Crick model).
What is the sugar–phosphate backbone?
The two outer side-rails of the ladder, made of sugar and phosphate, that hold the strands together. Sugar–phosphate backbone forms the outer rails; the two strands run antiparallel (5'→3' and 3'→5').
What are nitrogenous bases?
The 'letters' of the genetic code — A, T, G and C — that project inward from the rails to form the rungs. Nitrogenous bases point inward and pair up as the rungs: purines (A, G) and pyrimidines (T, C).
What is an A–T base pair?
Adenine always pairs with Thymine — like two puzzle pieces that only fit each other. Adenine pairs with Thymine via 2 hydrogen bonds (complementary base pairing).
What is a G–C base pair?
Guanine always pairs with Cytosine, held together a little more tightly. Guanine pairs with Cytosine via 3 hydrogen bonds — stronger than A–T.
What are hydrogen bonds?
Weak 'rungs' in the middle hold the two bases together — weak enough to unzip when DNA is copied. Hydrogen bonds between complementary bases: 2 for A–T, 3 for G–C.
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