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sub90 ESATsub90 ESAT SyllabusARCH-B-06
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UAT-UK SPEC: B5MODULE: BIOLOGYTOPIC ID: ARCH-B-06

DNA Base Composition (%A = %T, %G = %C), Triplet Coding Ratios & Point Mutations

Master DNA Base Composition (%A = %T, %G = %C), Triplet Coding Ratios & Point Mutations on the ESAT Biology paper. Traditional classroom derivations waste valuable seconds. Using the 2-step Sub-90 invariant elimination method compresses solve time to 30s, saving +95s per question.

Standard Classroom Time
125s
Textbook multi-line derivations bleed exam clock
Sub-90 Target Pace
30s
Comfortably below the 88.8s per-question limit
Time Saved for Review
+95s
Banks clock buffer across 27 questions

2-Step Sub-90 Shortcut Formula

How to eliminate intermediate algebra and solve under 45 seconds.

Launch Interactive Lesson
STEP 1 • SETUP INVARIANT (LINE 1)10–15s
Line 1 (50% Purine-Pyrimidine Invariant): In dsDNA, %A+%G=50%\%\text{A} + \%\text{G} = 50\% ALWAYS.

Establish the structural invariant and eliminate impossible options immediately.

STEP 2 • FAST SOLVE (LINE 2)15–25s
Line 2 (Subtract): %G=50%−18%=32%\%\text{G} = 50\% - 18\% = 32\% (10s).

Evaluate the simplified expression using integer factoring or unit elimination.

Distractor Trap Forensics

The predictable cognitive traps engineered by examiners into the wrong options.

TRAP #1factor_of_two_or_stoichiometry_trap

Calculating %G in double-stranded DNA with 20% A as (100 - 20)/2 = 40% instead of (100 - 40)/2 = 30%

Forgetting to subtract BOTH %A and %T (2 * 20% = 40%) from 100% before halving for %G.

Sub-90 Fix: Test invariants before expanding equations.
TRAP #2fence_post_or_domain_trap

Applying %A = %T to a SINGLE strand of DNA or mRNA instead of double-stranded DNA

Chargaff's rule (%A = %T, %G = %C) holds globally across the double helix, not within a single strand unless specified.

Sub-90 Fix: Test invariants before expanding equations.
TRAP #3factor_of_two_or_stoichiometry_trap

Dividing by 3 instead of multiplying by 3 when converting amino acids to coding DNA bases (or confusing base pairs with total bases = 2 * base pairs)

1 amino acid = 3 mRNA bases = 3 template DNA bases = 6 bases across both DNA strands.

Sub-90 Fix: Test invariants before expanding equations.

Try 1 Timed Question: DNA Base Composition (%A = %T, %G = %C), Triplet Coding Ratios & Point Mutations

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Full Lesson All 15 Questions (ARCH-B-06)
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ARCH-B-06: DNA Base Composition (%A = %T, %G = %C), Triplet Coding Ratios & Point Mutations (Sample)Biology
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SUB-90 ZONE (<40S)
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Question 1 of 1ARCH-B-06 (6-Card Lesson)Format: Standard 5-Option
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