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DNA and Replication
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History of DNA
Chromosomes are made of both DNA and protein
Radioactive 32P was injected into bacteria!
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5. Discovery of DNA Structure
Erwin Chargaff showed the amounts of the four bases on DNA ( A,T,C,G)
In a body or somatic cell:
__________ = 30.3%
__________ = 19.5%
__________ = 19.9%
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Chargaff’s Rule
__________________ must pair with __________________
The bases form weak _______________________________ T A G C
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DNA Structure
_____________________took diffraction x- ray photographs of DNA crystals
In the 1950’s, ____________________________________ ____________________________________ built the first model of DNA using Franklin’s x-rays
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Rosalind Franklin
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DNA Structure
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DNA
Two strands coiled called a _________________
Sides made of a pentose sugar __________________bonded to phosphate (PO4) groups by phosphodiester bonds
Center made of _______________________________________ _______________________________________ bonded together by weak ___________________
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DNA Double Helix
__________________________
“Rungs of ladder”
“Legs of ladder”
__________________________
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Helix
Most DNA has a ___________________________________ twist with 10 base pairs in a complete turn
Left twisted DNA is called Z-DNA or southpaw DNA
Hot spots occur where right and left twisted DNA meet
producing _____________________________________
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DNA
Stands for ______________________________________
Made up of subunits called ______________________________________
Nucleotide made of:
1. _____________________________
2. _____________________________
3. _____________________________
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DNA Nucleotide
O=P-O O
Phosphate
Group N
Nitrogenous base
(A, G, C, or T) O
CH2 O C1 C4 C3 C2 5
Sugar
(deoxyribose)
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Pentose Sugar
Carbons are numbered clockwise 1’ to 5’
CH2 O C1 C4 C3 C2 5
Sugar
(deoxyribose)
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DNA P O 1 2 3 4 5 P O 1 2 3 4 5 G C T A
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Antiparallel Strands
One strand of DNA goes from 5’ to 3’ (sugars)
The other strand is opposite in direction going 3’ to 5’ (sugars)
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Nitrogenous Bases
Double ring PURINES
Adenine (A)
Guanine (G)
Single ring PYRIMIDINES
Thymine (T)
Cytosine (C)
A or G
T or C
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Base-Pairings
Purines only pair with Pyrimidines
Three hydrogen bonds required to bond Guanine & Cytosine C G
3 H-bonds
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20. Two hydrogen bonds are required to bond Adenine & Thymine
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Question:
If there is 30% Adenine, how much Cytosine is present?
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