Download DNA Structure and Replication Integrated Science 4

DNA Structure and Replication
Integrated Science 4
Redwood High School
2/11
Name:
Per:
Procedure: Read pages 355-370 in chapter 17 of your Integrated Science textbook.
 The Structure of DNA
1. What three life sustaining tasks is DNA (genes) the basis of?
carry information one generation to the next
determining characteristics
easily copying itself (replicated)
2. DNA is a polymer formed from units called nucleotides.
3. What are nucleotides composed of?
Three parts:
• Phosphate group
• Deoxyribose sugar
• Nitrogenous base
4. Draw and label a typical nucleotide (see Figure 5)
5. What are the four nitrogenous bases present in DNA?
adenine (A), thymine (T)
guanine (G), cytosine (C)
6. Describe the work done by Rosalind Franklin. Include the limitation her data represented with respect to
determining the structure of DNA.
Rosalind Franklin used x-rays to visualize DNA.
Franklin’s work did not reveal the absolute structure of DNA.
The X pattern produced suggested DNA was composed of two strands twisted around each other with
nitrogenous bases oriented toward the center of the molecule.
7. Following Rosalind Franklin’s work, James Watson and Francis Crick established the structure of DNA.
Describe their work, including the relationship between nitrogenous bases within the DNA molecule.
Watson and Crick used models to construct the structure of DNA based on prior research.
They established the double helix (two strands wound around each other), and base pairing (based on hydrogen
bonds forming between A,T and G,C).
8. What did Erwin Chargaff contribute to Watson and Crick’s work? What did Chargaff discover?
Chargaff determined that the percentage of adenine (A) and tymine (T) bases were equal, as were the
percentages of guanine (G) and cytosine (C).
The percentages of corresponding bases was equal in almost any sample of DNA regardless of the organism
from which it came.
9. Describe the basic structure of a DNA molecule (pg. 357-358)
double helix – a pair of twisted strands bonded together by nitrogenous bases
10. What is meant by the phrase base-pairing? (very much related to number 8’s answer)
Nitrogenous bases are complimentary and will only bond with their compliment (A-T, G-C).
11. Complete this sentence: In DNA base-pairing, adenine pairs up with thymine, and cytosine always pairs up
with guanine.
12. Name and describe the type of bonding that joins individual strands of nucleotides together to form a DNA
double helix.
hydrogen bonds – weak bonds which are easily formed and broken link complimentary nitrogenous bases
together
covalent bonds – strong bonds which are not easily broken link phosphate groups to sugars of DNA strands
 The Replication of DNA
13. State when DNA must replicate itself. Follow this with a thorough description of what takes place during
DNA Replication.
DNA unzips exposing each strand of the double helix. These are the template strands.
DNA polymerase (special enzyme) uses each template strand to create a complimentary strand through basepairing (A-T)(C-G)
Replication produces two identical copies of the entire DNA molecule.
14. Critical Thinking: In your opinion, why is DNA replication considered necessary to life?
DNA replication takes place before cell division.
Cell division produces new cells to sustain an organism’s growth, maintenance, healing and reproduction.
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