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DNA: The Double Helix & Base Pairing

Students explore the structure of DNA — the twisted ladder that stores life’s instructions — and discover the base-pairing rule (A-T, G-C) that lets DNA copy itself with astonishing precision.

Grade 9Genetics55 minutes1 class period5E ModelExplicit teaching4 StandardsCommon Core
Start the Lesson
Lesson at a Glance

Everything you need before the bell rings

Learning Objectives

Students will be able to…

  • ✓Describe the double helix structure.
  • ✓Name the four bases.
  • ✓Apply the base-pairing rule.
  • ✓Explain how DNA copies itself.
Essential Question

A molecule inside every cell holds the complete instructions to build you — and can copy itself perfectly. How does DNA store and duplicate that information?

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Lesson Phases
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Vocabulary Terms
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Standards Aligned
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Interactive Task
DNA Builder · Interactive

The DNA Builder

Project this and tap the top bases to change them. Watch the bottom strand automatically pair up by the rule A-T and G-C.

🧬 Change the bases — watch them pair upTry it
Strand 1 (tap a base to change it) ↓

The Lesson · 5E Model

55 minutes, five moves

Tap any phase to open the teacher moves and student actions.

1

Engage — The Code of Life

5 min

One molecule holds all your instructions — and copies itself. How?

👩‍🏫 Teacher Moves

  • Introduce DNA as an instruction code.
  • Ask how it copies perfectly.
  • Set the goal: DNA structure.

🎒 Student Actions

  • Consider the code.
  • Wonder how.
  • Predict the structure.
2

Explore — Explore Base Pairing

12 min

Students investigate.

👩‍🏫 Teacher Moves

  • Send students to the DNA Builder.
  • Change bases; watch the pairs.
  • Record the rule.

🎒 Student Actions

  • Change the bases.
  • See the pairing.
  • Record the rule.
3

Explain — A-T, G-C

13 min

Teacher explains.

👩‍🏫 Teacher Moves

  • Describe the double helix.
  • Name the four bases.
  • Explain complementary pairing.

🎒 Student Actions

  • Learn the helix.
  • Name the bases.
  • Explain pairing.
4

Elaborate — Elaborate — Replication

12 min

Apply.

👩‍🏫 Teacher Moves

  • Show how pairing enables copying.
  • Predict a complementary strand.
  • Connect DNA to traits.

🎒 Student Actions

  • Explain copying.
  • Build a complement.
  • Connect to traits.
5

Evaluate — Evaluate — Exit Ticket

5 min

Three quick checks.

👩‍🏫 Teacher Moves

  • Hand out the exit ticket.
  • Look for the pairing rule.
  • Collect as formative data.

🎒 Student Actions

  • Name the bases.
  • Give a complement.
  • Explain copying.
Standards Alignment

Built to the standards you report on

Aligned to the Next Generation Science Standards (High School Life Science) and Common Core literacy in science.

NGSS
HS-LS1-1

Construct an explanation for how the structure of DNA determines the structure of proteins.

NGSS
HS-LS3-1

Explain how the structure of DNA determines the structure and traits of organisms.

NGSS
HS-LS1-6

Construct an explanation about the role of DNA and molecules in organisms.

CCSS
RST.9-10.7

Translate information in a text into a visual model.

Differentiation

One lesson, every learner

Multilingual Learners

ELL / EMERGING READERS
  • Color-coded base cards.
  • Sentence frame: “___ pairs with ___.”
  • Build a paper DNA model.

Support & Access

IEP / 504
  • Focus on A-T and G-C.
  • Use colored base tiles.
  • Give a strand to complete.

Stretch & Extend

GIFTED / EARLY FINISHERS
  • Explain transcription to RNA.
  • Model DNA replication.
  • Explain how mutations happen.
Materials

What to gather

  • 📽️Projector / board
  • 📓Science notebooks
  • 💻The DNA Builder
  • 🧱DNA model kit
  • ✏️Pencils
  • 🎫Exit-ticket slips
Vocabulary

Key terms — hover for a quick definition

DNAthe molecule that stores genetic instructionsdouble helixDNA’s twisted-ladder shapebaseone of the four DNA letters (A, T, G, C)base pairingthe rule A-T and G-Ccomplementarymatching by the pairing rulenucleotidea base + sugar + phosphate unitreplicationthe copying of DNAgenea segment of DNA coding for a trait
Evaluate

Exit Ticket

Preview the three formative checks. Tap “Sample answer” to see what mastery looks like — hide them before you print for students.

QUESTION 1
In DNA, what base pairs with adenine (A)?
Thymine (T).
QUESTION 2
If one DNA strand reads A-G-C, what is the complementary strand?
T-C-G.
QUESTION 3
Why does the base-pairing rule let DNA copy itself accurately?
Because each base only pairs with one partner, each strand acts as a template to rebuild an exact copy of the other.

Going deeper? From DNA to protein.

Have students follow how DNA is transcribed into RNA and then translated into a protein. A printable protein-synthesis sheet is in the Science library.

Study · Flashcards

Study the key terms

Tap a card to flip it, then rate whether you knew it. Built from this lesson’s vocabulary.

🃏 DNA & Base PairingFlip
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Term
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Meaning
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Practice · Quiz

Check your understanding

A quick self-check with instant feedback, drawn from this lesson’s key terms.

📝 DNA & Base PairingQuiz
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Question 1
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Practice · Worksheet

Printable worksheet

A print-and-go review sheet with a built-in answer key. Tap “Show answer key” to reveal answers, or print the clean version for students.

🖨️ DNA & Base PairingPrint
Name: ________________________
Date: ____________

Part A · Write the word that matches each meaning

Word bank: base, base pairing, complementary, DNA, double helix, gene, nucleotide, replication
  1. the molecule that stores genetic instructions
  2. matching by the pairing rule
  3. one of the four DNA letters (A, T, G, C)
  4. a segment of DNA coding for a trait
  5. the copying of DNA
  6. the rule A-T and G-C
  7. a base + sugar + phosphate unit
  8. DNA’s twisted-ladder shape

Part B · Show what you learned

  1. In DNA, what base pairs with adenine (A)?
  2. If one DNA strand reads A-G-C, what is the complementary strand?
  3. Why does the base-pairing rule let DNA copy itself accurately?
Answer key — Part A: 1) DNA · 2) complementary · 3) base · 4) gene · 5) replication · 6) base pairing · 7) nucleotide · 8) double helix
Part B: 1) Thymine (T). 2) T-C-G. 3) Because each base only pairs with one partner, each strand acts as a template to rebuild an exact copy of the other.