DNA Structure and Replication

Overview

Students learn how DNA structure relates to its function by exploring how DNA replication preserves genetic information. The lesson includes a short Do Now at the start and a 5-minute Gizmos simulation to model DNA building and replication.

Learning intentions

Students will:

• explain the roles of chromosomes, DNA and genes in heredity
• describe how DNA’s structure helps it copy during replication
• model DNA replication and use diagrams to show what is conserved and what is newly made
• use scientific explanations and evidence from the simulation to justify their predictions

Success criteria

Students can:

• correctly label or describe key parts of DNA (nucleotides, base pairs, sugar-phosphate backbone)
• explain why complementary base pairing allows DNA to replicate accurately
• represent replication steps in a simple sequence diagram
• use correct scientific language (gene, chromosome, DNA, nucleotide, base pairing) in their explanation

Curriculum links

• AC9S10U01: explain the role of meiosis and mitosis and the function of chromosomes, DNA and genes in heredity and predict patterns of Mendelian inheritance
• AC9S10U01 (elaboration): use models and diagrams to represent the relationship between genes, chromosomes and DNA
• AC9S10I01: develop explanatory models and reasoned predictions based on a tested model/simulation
• AC9S10H01 (light integration): recognise how scientific models (like simulations) help validate understanding through testing and refinement

Lesson structure (40 minutes)

1. 0–5 min · Do Now. Teacher displays three prompts: (1) What is DNA? (2) Where are genes located (choose one): nucleus / ribosomes / cell membrane (3) Give one reason DNA could be copied for offspring. Students respond individually in books; teacher collects 2–3 to check misconceptions.

2. 5–12 min · Mini-lesson: structure → function. Teacher draws a quick DNA “ladder” diagram and links: nucleotides (A, T, C, G) form base pairs; sugar-phosphate backbone provides stability; complementary strands guide copying. Students annotate their diagram with teacher-provided labels and complete a sentence starter: “DNA can replicate because…”

3. 12–17 min · Gizmos build a DNA molecule (5 min). Teacher explains the task: use Gizmos to build one DNA molecule; observe how choosing a base on one strand determines the partner base on the other strand. Students complete the simulation, then record: (a) one base pair relationship they noticed and (b) what remained the same between strands.

4. 17–27 min · Replication modelling with diagrams. Teacher provides a simple replication template (two-step flow: strand separation → new strand formation using base pairing). Students work in pairs to recreate replication using cut-out “nucleotides” (or pre-printed cards): place complementary bases and draw the two resulting DNA molecules (semiconservative replication concept emphasised as “one old strand + one new strand”).

5. 27–35 min · Concept check: explain in words. Teacher prompts: “Use your diagram to explain how DNA structure supports accurate replication.” Students write a 5–6 sentence explanation using word bank: chromosome, gene, DNA, nucleotide, base pair, replicate, complementary.

6. 35–40 min · Exit ticket. Students answer two items: (1) Circle the statement that best explains accurate copying: “bases do/don’t match in a predictable way” (2) Predict: if A pairs with T, what pairs with G? Explain in 1–2 lines.

Resources

• Gizmos “Build a DNA molecule” simulation loaded and ready on devices
• Student notebooks and pens
• Replication diagram templates (strand separation and new strand formation)
• Nucleotide base cards (A, T, C, G) or printable cut-outs
• Word bank for sentence writing
• Exit ticket slips or a digital form

Assessment

• Collect Do Now for quick misconceptions (genes location and DNA copying reason)
• Observe Gizmos participation and check recorded base-pair relationship
• Mark exit ticket for base pairing accuracy and a coherent explanation of replication

Differentiation

• Support:
• Provide sentence starters and a partially labelled DNA diagram for students who need scaffolding
• Offer a smaller base-pairing rule sheet (A–T, C–G) and prompt cards during the replication modelling activity
• Pair students strategically so each team has at least one confident modeller and one recorder
• Consolidation for students who struggle:
• Allow students to complete only one replication template fully, then summarise the remaining concept in words
• Use “turn and talk” checkpoints before written explanations
• Extension for advanced learners:
• Ask: “Where in the cell cycle does DNA replication happen and why is accurate copying essential for cell division?” (keep responses conceptual, not overly detailed)
• Challenge: predict what would happen to replication if a base pairing rule were incorrect, and connect to mutations conceptually
• EAL/SEN considerations:
• Use consistent vocabulary and display it throughout (word bank; definitions in plain language)
• Provide visual cues (arrows showing strand separation and new strand growth)