12.2 The Structure of DNA
A 9. nucleotide 10.nitrogenous base (adenine) hydrogen bonds deoxyribose sugar 8. 11. G C A G G C 13. A T T C phosphate group 12. base pair (guanine and cytosine)
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5. The nucleotides in DNA are joined by bonds.
covalent
2. Nucleotides in DNA are made of three basic components: a sugar called: , a , and a nitrogenous .
deoxyribose; phosphate; base
1. The building blocks of DNA are
nucleotides
4. In DNA, can be joined in any order.
nucleotides
14. The drawing below shows half of a DNA molecule. Fill in the appropriate letters for the other half. Explain why you drew your sketch the way you did. CG AT GC GC CG CG TA AT CG The bases link with hydrogen bonds in pairs across the "rungs" of the ladder: A with T and G with C.
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15. Complete this table to show how the structure of the DNA molecule allows it to perform each essential function. Key A = Adenine C = Cytosine G = Guanine T = Thymine Function Structure of the Molecule Store information Each strand of the double helix carries a sequence of bases, arranged something like letters in a four-letter alphabet. Copy information The base pairs can be copied when hydrogen bonds break and the strands pull apart. Transmit information When DNA is copied, the sequence of base pairs is copied, so genetic information can pass unchanged from one generation to the next.
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6. Complete the table to describe each scientist's contribution to solving the structure of DNA. Scientist Contribution Rosalind Franklin Took X-ray diffraction pictures that revealed the double-helix structure of DNA. Built a model of the DNA molecule that explained both the Crick structure and the properties of DNA. 7. Complete the table by estimating the percentages of each based on Chargaff's rules. 3 33 33 17 17 The Double-Helix Model For Questions 8-13, on the lines provided, label the parts of the DNA molecule that correspond to the numbers in the diagram. James Watson and Francis
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3. DNA contains four kinds of nitrogenous bases:
adenine , thymine , guanine , and cytosine .
