The structure of DNA

Grade 9 Science Worksheet - Challenge Me

Circle the best answer.

1. 1.

   Model strands (not to scale). Strand 2 is its partner, with bases and ends not shown. Tala has the model strand 5′-CCGATA-3′. Its partner strand is written from its own 5′ end. Which choice is the partner?

   • 5′-GCGATT-3′
   • 5′-ATAGCC-3′
   • 5′-GGCTAT-3′
   • 5′-TATCGG-3′
2. 2.

   Kira swaps one A–T rung in a model for an A–G rung. Using the ring card, what happens to the width at that rung?

   • It stays the same, because A and G also pair with each other
   • It gets narrower, because G is smaller than T
   • It stays the same, because a rung spans 3 rings
   • It gets wider, because A–G spans 4 rings and A–T spans 3

3. Read this first

   Use this

   Model data card (number of pairs). Columns: pair type, number of pairs. A–T before the swap: 5. C–G before the swap: 5. Pairs swapped from A–T to C–G: 3.

4. 3.

   Zee builds a model with 5 A–T and 5 C–G pairs, then swaps 3 A–T pairs for C–G pairs. How many hydrogen bonds does the ladder have after the swap?

   • 25
   • 28
   • 22
   • 34

5. Use this

   Measurement card (Data: OpenStax Biology 2e). Columns: measure, value. Distance between base pairs: 0.34 nm. Base pairs per turn: 10. Width of the double helix: 2 nm. A model ladder has 30 base pairs before and 60 base pairs after it is extended.

6. 4.

   Bo extends a model ladder from 30 to 60 base pairs, using the measurement card. What changes?

   • Length doubles to 20.4 nm, turns double to 6, and width stays 2 nm
   • Length doubles to 20.4 nm, turns stay at 3, and width stays 2 nm
   • Length doubles to 20.4 nm, turns double to 6, and width doubles to 4 nm
   • Length rises to 204 nm, turns double to 6, and width stays 2 nm

7. Use this

   Notebook (model data), 4 rows. Columns: line, what it says. 1, The two strands run in opposite directions. 2, The sugar-phosphate backbone forms the outer rails. 3, A pairs with T and C pairs with G. 4, A–T has 3 hydrogen bonds and C–G has 2.

8. 5.

   Pia reviews a classmate's notebook on DNA structure. Exactly one line is wrong. Which line, and why?

   • Line 2, because the rails are made of bases
   • Line 1, because both strands run the same way
   • Line 3, because A pairs with G and C pairs with T
   • Line 4, because A–T has 2 hydrogen bonds and C–G has 3

9. Use this

   Notebook (model data), 4 rows. Columns: line, what it says. 1, A pairs with T and C pairs with G. 2, The two strands run in the same direction, with both 5′ ends at the left. 3, The bases sit between the two backbones. 4, A–T has 2 hydrogen bonds.

10. 6.

    Esme reviews a second notebook on DNA structure. Exactly one line is wrong. Which line, and why?

    • Line 4, because A–T has 3 hydrogen bonds
    • Line 2, because the strands run in opposite directions
    • Line 3, because the rails are built from bases
    • Line 1, because A pairs with G and C pairs with T

11. Use this

    Notebook (real dates and places), 4 rows. Columns: line, what it says. 1, Franklin used X-ray diffraction on DNA in the lab of Maurice Wilkins at King's College London. 2, With Raymond Gosling, Franklin made a clear X-ray photo of the B form of DNA in May 1952. 3, Watson and Crick took that photo at the University of Cambridge. 4, Watson and Crick's paper appeared in Nature on 25 April 1953.

12. 7.

    Luz reviews a notebook on the history of the double helix. Exactly one line is wrong. Which line, and why?

    • Line 2, because the photo was made after the paper
    • Line 3, because the photo came from Franklin's work, not theirs
    • Line 4, because the paper appeared in 1962
    • Line 1, because Franklin worked at Cambridge

13. Use this

    Model data card, percent of the bases in four two-stranded samples. Columns: sample, A, T, G, C. P: 31, 31, 19, 19. Q: 22, 22, 28, 28. R: 30, 20, 25, 25. S: 27, 27, 23, 23.

14. 8.

    Ren checks four model samples against Chargaff's rule. Which sample cannot be a complete two-stranded DNA?

    • Sample R, because A and T are not equal
    • Sample Q, because its percents are not 25 each
    • Sample P, because A and C are not equal
    • Sample S, because A and G are not equal

15. Use this

    History card (real dates). 1952: Rosalind Franklin with Raymond Gosling, at King's College London, make an X-ray photo of the B form of DNA, labeled 51. 1953: James Watson and Francis Crick, at the University of Cambridge, publish a double-helix model built with Franklin's X-ray data on 25 April; Franklin and Gosling publish a paper in the same issue of Nature. 1962: Francis Crick, James Watson and Maurice Wilkins receive the Nobel Prize in Physiology or Medicine; Franklin is no longer living, and the prize is not awarded after death.

17. 9.

    Jun uses the history card to place Franklin's photo. Which statement does the card support?

    • The photo was made in 1953, after the model, to test the model
    • The photo was made in 1952 by Watson and Crick, who then wrote the 1953 paper
    • The photo was made in 1962, the year of the prize, by Watson and Crick
    • The photo was made in 1952, before the 1953 papers, and the model used Franklin's data
18. 10.

    Milo uses the history card. How many years passed between the X-ray photo labeled 51 and the Nobel Prize, and who made the photo?

    Use the picture in question 9.

    • 10 years; the photo was made by Watson and Crick
    • 9 years; the photo was made by Franklin and Gosling
    • 9 years; the photo was made by Wilkins, who showed it to Watson
    • 10 years; the photo was made by Franklin and Gosling