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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 DNA
______ 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?
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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?
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Directed Reading A continued
Match the correct description with the correct term. Write the letter in the space
provided.
a. cytosine
______19. pairs with adenine
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?
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Section Review
What Does DNA Look Like?
USING KEY TERMS
1. Use the term DNA in a sentence.
2. In your own words, write a definition for the term nucleotide.
UNDERSTANDING KEY IDEAS
3. List three important events that led to understanding the structure of DNA.
______ 4. Which of the following is NOT part of a nucleotide?
a. base
b. sugar
c. fat
d. phosphate
MATH SKILLS
5. If a sample of DNA contained 20% cytosine, what percentage of guanine
would be in this sample? What percentage of adenine would be in the sample?
Explain. Show your work below.
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Section Review continued
CRITICAL THINKING
6. Making Inferences Explain what is meant by the statement “DNA unites all
organisms.”
7. Applying Concepts What would the complementary strand of DNA be for the
sequence of bases below?
CTTAGGCTTACCA
8. Analyzing Processes How are copies of DNA made? Draw a picture as part of
your answer.
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Genes and DNA