1. The Structure of DNA
Pre-AP Biology
11/10/2018

2. Bellwork
Examine the organisms on the next slide and list 5 characteristics that make them unique.
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3. Different Biological Organisms found on Planet Earth
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4. Objectives Describe the structure of DNA.
List the components that make up a nucleotide.
Distinguish between a purine and pyrimidine.
Explain complementary base pairing
Identify the proteins involved in DNA replication.
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5. Key Terminology Nucleotide Deoxyribose sugar Purine Pyrimidine
Complementary base pairing
Antiparallel
Hydrogen bonding
Helicase
DNA Polymerase
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6. DNA DNA stands for deoxyribonucleic acid Function of DNA
Storage of genetic information that determines the characteristics of the organism
Structure of DNA
Made of two strands
Each strand is a polymer of nucleotides
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7. Composition of a Nucleotide
A nucleotide has three components:
A phosphate group
Deoxyribose sugar
a 5 carbon sugar
Nitrogenous base

8. Nitrogenous bases in a nucleotide can be further classified as
Pyrimidines-single ring structure
(T) Thymine
(C) Cytosine
Purines – double ring structure
(A) Adenine
(G) Guanine
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9. DNA molecule is a double helix
Two strands of nucleotides are twisted in a helical shape
The two strands are antiparallel
meaning they run in opposite directions
The strands are held together by hydrogen bonds
a weak bond between the strands
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10. PROPERTY OF PIMA COUNTY JTED, 2010
Think-Pair-Share
Give an everyday analogy that would illustrate the term antiparallel. Explain how this everyday analogy is related to the antiparallel nature of the two strands of DNA.
3. Think-pair-share
teacher presents a question
teacher gives wait time for student to form answer
teacher instructs students to share their answer with a partner
teacher calls on non-volunteers to share with the class
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11. Chargoff’s Observations
Edwin Chargoff, an American Biochemist examined the
% composition of nitrogenous bases (adenine, guanine, thymine, and cytosine) in different organisms.
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12. PROPERTY OF PIMA COUNTY JTED, 2010
Think-Pair-Share
Examine the numbers in the table on the next slide and write down trends you observe in your note-taker. Compare your observations with the person next to you.
3. Think-pair-share
teacher presents a question
teacher gives wait time for student to form answer
teacher instructs students to share their answer with a partner
teacher calls on non-volunteers to share with the class
PROPERTY OF PIMA COUNTY JTED, 2010 3

13. Chargoff’s Data Human 31.0 31.5 19.1 18.4 Fruit Fly 27.3 27.6 22.5
Species
Adenine (%)
Thymine (%)
Guanine (%)
Cytosine (%)
Human
31.0
31.5
19.1
18.4
Fruit Fly
27.3
27.6
22.5
Corn
25.6
25.3
24.5
24.6
Yeast
23.0
23.3
27.1
26.6
Bacteria
24.3
25.5
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14. Key Observations
Guanine approximately equal to cytosine; adenine approximately equal to thymine
Suggests that G always pairs with C and
A always pairs with T
In other words, a purine always pairs with a pyrimidine
These pairs are referred to as complementary base pairs
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15. Significance of Complementary Base Pairs
Based on complementary base pair rules, the sequence of nucleotides on one strand determines the sequence of nucleotides on the other strand.
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16. Sample Problem
For the nucleotide sequence of the DNA strand below, write on your note-taker the complementary strand. Remember A pairs with T and G pairs with C:
Strand 1: A T G G C A C T A G C A A
Strand 2:
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17. DNA synthesis
New copies of DNA are made by a biochemical process known DNA replication
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18. DNA replication involves a complex of proteins
These proteins are:
DNA Helicase – opens the double helix
Single-stranded binding protein – keeps the two strands separated
DNA polymerase – adds nucleotides that are complementary to the DNA template

19. DNA Replication New DNA made by the enzyme DNA polymerase
During DNA replication, each strand of the original DNA is used as the template
DNA polymerase synthesizes the complementary new strand
DNA replication is considered semi-conservative. Why?
Keeps one original strand and makes one new strand

20. DNA replication

21. Closure Activity: Rope Ladder analogy: Explain how DNA is like/different from a rope ladder.