The structure of DNA

Grade 9 Science Worksheet

Circle the best answer.

1. 1.

   Bottom strand directly beneath it: six bases, ends not labeled. Luz writes the bottom strand under 3′-TACGGA-5′. Which choice gives the bottom strand, read from its own 5′ end?

   • 5′-CGTAAG-3′
   • 5′-TCCGTA-3′
   • 5′-TACGGA-3′
   • 5′-ATGCCT-3′

2. Read this first

   Use this

   Ladder (model, not to scale).

3. 2.

   Milo writes the bottom strand under 5′-GATCCG-3′, left to right as it sits beneath. Which choice is correct, with its end labels?

   • 3′-GATCCG-5′
   • 3′-AGCTTA-5′
   • 3′-CTAGGC-5′
   • 5′-CTAGGC-3′
4. 3.

   Pia completes the bottom strand under 3′-ATGGCA-5′. Which letters fill the blanks, left to right?

   • A, C, T
   • C, A, G
   • A, G, T
   • T, C, A
5. 4.

   Ladder (model, not to scale). Bottom strand directly beneath: five bases, to find. Zee counts the hydrogen bonds in a short stretch whose top strand is 3′-GATTC-5′. How many hydrogen bonds join the five base pairs?

   • 10
   • 15
   • 12
   • 13
6. 5.

   (model, not to scale). Ari studies one nucleotide of the top strand. Arrow Y points to the part that faces the other strand. What is Y?

   • The base, which pairs with a base on the other strand
   • The sugar, which links to the other strand
   • The hydrogen bond, which is a part of each single nucleotide
   • The phosphate, which links to the other strand
7. 6.

   Tala compares two stretches of DNA with the same number of base pairs. Which stretch has more hydrogen bonds, and why?

   • Neither, because both stretches have 5 base pairs
   • Stretch N, because it has more C–G pairs, with 3 bonds each
   • Stretch N, because C–G pairs are the smaller pairs
   • Stretch M, because A–T pairs have 3 bonds each

8. Use this

   Model data card, percent of the bases in a two-stranded sample. A: 28. T: ?. G: ?. C: ?. Total: 100.

9. 7.

   Bo reads a model sample of two-stranded DNA. Adenine is 28% of the bases. What percent of the bases is guanine?

   • 44%
   • 28%
   • 36%
   • 22%

10. Use this

    Model data card, percent of the bases in a two-stranded sample. A: ?. T: 31. G: ?. C: ?. Total: 100.

11. 8.

    Ren reads a second model sample of two-stranded DNA. Thymine is 31% of the bases. What percent of the bases is cytosine?

    • 69%
    • 31%
    • 19%
    • 38%
12. 9.

    Model data card, number of bases in a two-stranded sample. A: 240. T: ?. G: ?. C: ?. Total: 1,000. Jun counts the bases in a model sample of two-stranded DNA with 1,000 bases. Adenine is 240 of them. How many bases are cytosine?

    • 260
    • 520
    • 380
    • 240

13. Use this

    Who-did-what card (real facts from OpenStax Biology 2e and NIH NLM). Columns: person, place, work. Rosalind Franklin with Raymond Gosling, King's College London, X-ray photo of the B form of DNA in 1952, labeled 51. James Watson and Francis Crick, University of Cambridge, built the double-helix model in 1953 using Franklin's X-ray data.

14. 10.

    Esme says Watson and Crick took the X-ray photo labeled 51. Using the card, which reply is best?

    • Correct: Watson and Crick took it at Cambridge in 1952
    • Not correct: Franklin and Gosling made the photo, and the model used it
    • Not correct: the photo was made in 1962, after the prize
    • Not correct: Franklin joined the work after the 1953 model