1. Figure 12–7 Structure of DNA
Section 12-1
Nucleotide
Hydrogen bonds
Sugar-phosphate backbone
Key
Adenine (A)
Thymine (T)
Cytosine (C)
Guanine (G)

2. NUCLEIC ACIDS are built from subunits called ____________________
NUCLEOTIDES
SUGAR in DNA is
________________
Image by: Riedell
deoxyribose

3. DEOXYRIBONUCLEIC ACID
DOUBLE
______________ STRANDED
Backbone
(sides of ladder)
made of
_____________
and
PHOSPHATES
sugars
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4. Nitrogen bases =“Steps of ladder”
Purines (2 rings)
Phosphate group G C
Pyrimidines
(1 ring)
Deoxyribose sugar T
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5. NITROGEN BASES in DNA ADENINE GUANINE CYTOSINE THYMINE No URACIL

6. CHARGAFF’S RULES A = T G = C _________ _________
_________ _________
At time no one knew why…
now we know its because
Adenine always bonds across with____________
Guanine always bonds across with ____________
THYMINE
CYTOSINE
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7. DOUBLE HELIX Hydrogen _____________ bonds
between nitrogen bases hold the two strands together.
Hydrogen
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8. Nitrogen Base Pairing Bases can be in any order along one side of DNA
Strands are complementary
Complementary – a DNA strand which is able to bond to another strand according to the base-pairing rule
A always pairs with T
C always pairs with G
While any order of bases is possible along one side of DNA, the other strand must have the complementary nitrogenous bases to bond correctly.
According to base pairing rules of DNA, A will pair with T and C will pair with G. Notice that this pairs a specific purine with a specific pyrimidine. If a strand of DNA can bond to another strand, the strands are said to be complementary to each other.

9. Chromosomes
A replicated chromosome can be unwound to reveal a structure of loops and coils of proteins and DNA.

10. A T C G
Isn’t this a great illustration!?

11. When does a cell copy DNA?
When in the life of a cell does DNA have to be copied?
cell reproduction
mitosis
gamete production
meiosis
when cells divide, they must duplicate DNA exactly for the new “daughter” cells
Why is this a good system?