Candy Code Sequence

Partner Quality Audit: Partner Sign-off: _________________

All 12 pairs follow A-T & C-G

Twizzler backbones secure

Helical 3D twist stable

Part 4: Structural Analysis & Competency Explanations

Standard BIO.1C: Model Evaluation

1. Spatial Geometry: Why must a purine (Adenine/Guanine) always pair with a pyrimidine (Thymine/Cytosine)? What physical defect would occur in your candy model if Adenine paired with Guanine?

2. Bond Strength Difference: In a cell, the sugar-phosphate backbone is held by strong covalent bonds, while bases pair via weak hydrogen bonds. Why is this difference in bond strength essential for replication?

3. Predictive Synthesis: If an organism's DNA contains 300 base pairs (600 total bases) and 70 of those bases are Guanine, calculate the exact number of Thymine bases present in this DNA molecule:

Preserve completed candy double helix for Day 2 Replication Lab! Page 2 of 2

1 Old Parent Strand 1 New Synthesized

Daughter Molecule 2

1 Old Parent Strand 1 New Synthesized

Essential Takeaway: Neither daughter molecule is completely brand new! Each contains exactly one conserved original strand and one newly assembled strand.

Candy Lab Replication Protocol

Hands-On Phase 2

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Step 1: Helicase Action

Gently untwist your Day 1 helix back into a flat ladder. Using lab scissors (or clean hands), snip the 12 toothpick rungs in half down the middle to separate the two parent strands.

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Step 2: Collect New Substrates

Obtain 2 new Twizzlers (different flavor/color if available, representing new sugar-phosphate strands) and 24 new matching candy bases + 12 fresh toothpicks.

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Step 3: DNA Polymerase Synthesis

For each separated parent strand, build a matching complementary daughter strand following base pairing rules: Green (A) with Red (T), Yellow (C) with Blue (G).

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Step 4: Twist Two Identical Helices

Attach the new backbone Twizzlers. Twist both models! Place them side-by-side: verify they have 100% identical sequence order.

Competency Checkpoint: Do both resulting candy helices have the exact same 12-base sequence? Check with partner!

What If a Base Mismatches? Mutations

Proofreading

DNA Polymerase has an exonuclease "backspace" feature. But if an incorrect base escapes correction, a mutation is permanent.

Mismatched Base Pair Simulation

Imagine your partner placed a Green (A) across from a Blue (G).

A (Purine) + G (Purine) = Helix Bulge Error!

The hydrogen bonds fail to align correctly, warping the backbone shape and triggering repair enzymes.

Polymerase Proofreading Power

DNA Polymerase senses structural distortions immediately.

It reverses direction, removes the incorrect nucleotide, and inserts the proper complementary partner before moving forward.

Overall Error Rate: ~1 mistake per 1 billion bases replicated!

Record your error analysis and partner proofreading audit in Part 2 of your assessment guide now.

Competency Assessment Task

Summative Evidence

Today's 3-Part Demonstration of Mastery:

1. Lab Model Evidence

Show teacher your two replicated helices. Explain which strands are conserved parent strands and which are newly synthesized daughter strands.

2. Written Synthesis

Answer the 3 mechanistic questions on Page 1 comparing Helicase, Polymerase, and the semi-conservative model.

3. Mastery Exit Ticket

Independently complete the 5-item knowledge check on Page 2 (sequence matching, mutation detection, and 3-2-1 exit reflection).

Lab Clean-Up Protocol:

Once your model is scored on the rubric, toothpicks go in trash; candies can be enjoyed!

Begin Assessment

Refer to the Competency Rubric on your assessment sheet to confirm your target mastery level.

Part 3: Mechanistic Written Explanations

Connecting tactile lab observations to cellular biochemistry

Written Evidence

1. Enzymatic Specialization: In the candy lab, you used scissors to cut toothpicks, then added new toothpicks and candies. Compare the biological roles of DNA Helicase and DNA Polymerase in this sequence:

2. Error Prevention & Proofreading: Why is complementary base pairing (A with T, C with G) critical for minimizing replication mutations? What happens when a mismatched base is inserted?

Individual Task

Part 4: Mastery Check Exit Ticket

Independent Completion • 10 Minutes

Task 1: Replication Sequence Synthesis — Provide the newly synthesized complementary strand for the template below:

Template Strand: 3' - A G C T T A C G C T A A - 5'

Daughter Strand: 5' - _______________________________ - 3'

Task 2: Mutation Spotter Scenario — A sequencing machine reads the following replicated segment. Circle the error and explain:

Strand A:  5' - T A C C G A T T A - 3' | | | | | | | | | Strand B:  3' - A T G G C T A C A - 5'

Identify the mismatch and explain how DNA Polymerase corrects this during replication:

Task 3: 3-2-1 Quick Reflection

3 Key Terms:

2 Enzymes:

1 Wonder/Question:

Turn in completed assessment with lab evidence for competency sign-off Page 2 of 2