The structure of DNA

Grade 9 Science Worksheet - Building Confidence

Circle the best answer.

1. 1.

   Ari labels a paper model of DNA. Arrow W points to the long outer line of the top strand. What is W?

   • The sugar-phosphate backbone, a chain of sugars and phosphates
   • A line of hydrogen bonds holding the two strands together
   • A stack of base pairs, one resting on the next one
   • A row of bases, because the bases form the outer lines
2. 2.

   Esme outlines one unit on the model. Outline Y circles a five-sided shape, a round shape and a lettered block, joined together. What is Y?

   • A hydrogen bond: a weak link between two bases
   • A backbone: a long chain of sugars and phosphates
   • A base pair: two bases, one from each strand
   • A nucleotide: one sugar, one phosphate and one base
3. 3.

   Jun fills in a paper ladder. Which base goes in the blank, directly under adenine (A)?

   • Cytosine (C), the partner of guanine
   • Thymine (T), the partner of adenine
   • Guanine (G), because both bases have double rings
   • Adenine (A), because matching letters go together
4. 4.

   Kira fills in a second paper ladder. Which base goes in the blank, directly under cytosine (C)?

   • Adenine (A), the partner of thymine
   • Thymine (T), because both bases have single rings
   • Guanine (G), the partner of cytosine
   • Cytosine (C), because matching letters go together
5. 5.

   Ladder (model, not to scale). Luz completes the bottom strand under A, C, G. Which three bases fill the blanks, left to right?

   • C, G, T
   • G, T, A
   • T, G, C
   • A, C, G
6. 6.

   Two drawings of rungs (not to scale). Noah checks which drawing pairs the bases correctly. Which case is correct?

   • Case 2, because A pairs with T and C pairs with G
   • Case 1, because A pairs with G and C pairs with T
   • Case 2, because each rung joins two single-ring bases
   • Case 1, because bases with matching ring counts pair up
7. 7.

   “Two drawings (not to scale). Columns:” Pia compares two drawings of a short stretch of DNA. Which case puts the parts in the right places?

   • Case A, because the bases need to be outside to pair up
   • Case B, because the phosphates join the two strands in the middle
   • Case A, because the bases form the long outer lines
   • Case B, because the bases meet inside the chains
9. 8.

   Ren reads a history card. According to the card, who made the X-ray photo labeled 51?

   • Maurice Wilkins, who received the 1962 prize
   • Rosalind Franklin, with Raymond Gosling
   • James Watson and Francis Crick, at Cambridge
   • Raymond Gosling, working alone
10. 9.

    Tala reads the same history card. Where did Watson and Crick get X-ray data for their double-helix model?

    Use the picture in question 8.

    • From an X-ray photo they took themselves at Cambridge
    • They used no X-ray data and built the model from parts
    • From Franklin's X-ray work at King's College London
    • From the 1962 prize paper, written after the model
11. 10.

    Card of base-pair facts (Data: OpenStax Biology 2e). Columns: base pair, hydrogen bonds. A–T: 2. C–G: 3. Zee reads a card of facts about base pairs. How many hydrogen bonds join a C–G pair?

    • 3 hydrogen bonds
    • 5 hydrogen bonds
    • 1 hydrogen bond
    • 2 hydrogen bonds