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Name ______________________________ Class___________________Date__________________ Skills Worksheet Directed Reading A Section: What Does DNA Look Like? _____ 1. What are chromosomes made of? a. inherited characteristics c. cells and structures b. generations d. protein and DN _____ 2. What is the name of the material that determines inherited characteristics? a. deoxyribonucleic acid c. RNA b. ribosome d. amino acid THE PIECES OF THE PUZZLE 3. The subunits that make up DNA are called a. phosphates. c. amino acids. b. nucleotides. d. bases. 4. What two things must DNA be able to do? ____________________________________________________________________ ____________________________________________________________________ 5. Why must DNA be able to be copied? ____________________________________________________________________ ____________________________________________________________________ 6. Scientists were surprised about how much the DNA molecule could do, because they thought only _______________________ molecules could give instructions and be copied during cell division. 7. What three things is a nucleotide made of? ____________________________________________________________________ ____________________________________________________________________ ____________________________________________________________________ 8. What are the four bases of a nucleotide? ____________________________________________________________________ ____________________________________________________________________ ____________________________________________________________________ ____________________________________________________________________ Original content Copyright © by Holt, Rinehart and Winston. Additions and changes to the original content are the responsibility of the instructor. Holt Science and Technology 1 Genes and DNA Name ______________________________ Class___________________Date__________________ Directed Reading A continued 9. What four letters stand for the four types of bases? ____________________________________________________________________ 10. According to Chargaff’s rules, the amount of _______________________ always equals the amount of thymine. 11. According to Chargaff’s rules, the amount of guanine always equals the amount of _______________________. 12. Rosalind Franklin used a process known as _______________________ to make images of DNA molecules. 13. What shape did Franklin’s images show? ____________________________________________________________________ 14. What did James Watson and Francis Crick’s model of DNA look like? ____________________________________________________________________ ____________________________________________________________________ 15. What two things did this model eventually help explain? ____________________________________________________________________ ____________________________________________________________________ DNA’S DOUBLE STRUCTURE 16. The twisted ladder shape of DNA is called a(n) ______________________ 17. What molecules form the sides of the ladder? ____________________________________________________________________ ____________________________________________________________________ 18. What are the rungs of the DNA ladder made of? ____________________________________________________________________ Original content Copyright © by Holt, Rinehart and Winston. Additions and changes to the original content are the responsibility of the instructor. Holt Science and Technology 2 Genes and DNA Name ______________________________ Class___________________Date__________________ Directed Reading A continued Match the correct description with the correct term. Write the letter in the space provided. _____ 19. pairs with adenine a. cytosine b. thymine _____ 20. pairs with guanine 21. How did the double helix structure match Chargaff’s observations? ____________________________________________________________________ ____________________________________________________________________ MAKING COPIES OF DNA 22. The pairing of bases allows the cell to ______________________, or make copies of DNA. 23. Both sides of a DNA molecule are ______________________, binding only with their match. 24. Where is a molecule split during replication? ____________________________________________________________________ 25. After a DNA molecule splits, what is added to each side of the ladder? ____________________________________________________________________ 26. How often is DNA copied? ____________________________________________________________________ 27. What in the cell helps with unwinding, copying, and rewinding the DNA? ____________________________________________________________________ Original content Copyright © by Holt, Rinehart and Winston. Additions and changes to the original content are the responsibility of the instructor. Holt Science and Technology 3 Genes and DNA