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Biology · Grades 9–12

DNA base pairing and transcription

Study guide for Grades 9 to 12: 2 worked examples and 2 practice questions. Bases pair by shape and hydrogen bonding: adenine with thymine (uracil in RNA) and cytosine with guanine. Work one base at a time.

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Rule and key idea

Bases pair by shape and hydrogen bonding: adenine with thymine (uracil in RNA) and cytosine with guanine. Work one base at a time.

DNA: A-T, C-G · RNA: A-U, C-G

Worked examples

A DNA template strand reads AAGCCT. Which mRNA sequence is transcribed from it, read base by base in the same order?

AAGCCT → UUCGGA (A-U, T-A, C-G, G-C)

UUCGGA

A DNA template strand reads CCAGCTTCT. Which mRNA sequence is transcribed from it, read base by base in the same order?

CCAGCTTCT → GGUCGAAGA (A-U, T-A, C-G, G-C)

GGUCGAAGA

Try two questions

  1. Using base-pairing rules, which sequence pairs with the DNA strand TACCGGAAC, read base by base in the same order?

    1. ATGGCCTCG
    2. TACCGGAAC
    3. AUGGCCUUG
    4. ATGGCCTTG

  2. Using base-pairing rules, which sequence pairs with the DNA strand TGTTGAC, read base by base in the same order?

    1. ACAACTG
    2. ACAACUG
    3. ACACCTG
    4. TGTTGAC

Answers and reasoning

Answers and marking notes
  1. ATGGCCTTG

    TACCGGAAC → ATGGCCTTG (A-T, C-G)

  2. ACAACTG

    TGTTGAC → ACAACTG (A-T, C-G)

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