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ABBREVIATIONS
LWBK771-FM_pi-xvi.qxd 9/30/10 1:33 PM Page xiv Aptara Inc
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ABBREVIATIONS
LWBK771-FM_pi-xvi.qxd 9/30/10 1:33 PM Page xv Aptara Inc
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ABBREVIATIONS
LWBK771-FM_pi-xvi.qxd 9/30/10 1:33 PM Page xvi Aptara Inc
1
The Biochemistry of Nucleic Acids (Figure 1-1).
A nucleoside consists of a
nitrogenous base and a sugar. A nucleotide consists of a nitrogenous base, a sugar, and a
phosphate group. DNA and RNA consist of a chain of nucleotides, which are composed of
the following components:
A. NITROGENOUS BASES
1.
Purines
a.
Adenine (A)
b.
Guanine (G)
2.
Pyrimidines
a.
Thymine (T)
b.
Cytosine (C)
c.
Uracil (U) which is found in RNA
B. SUGARS
1.
Deoxyribose
2.
Ribose which is found in RNA
C.
PHOSPHATE (PO
4
3
)
O
Nitrogenous Bases
Purines
Pyrimidines
Sugars
Phosphate
Adenine (A)
Guanine (G)
Cytosine (C)
Uracile (U)
Thymine (T)
NH
2
C
N
HC
C
N
C
N
CH
N
H
O
1
6
5
4
3
2
7
8
9
C
N
C
C
N
C
N
CH
N
H
1
6
5
4
3
2
7
8
9
H
2
N
C
N
H
C
CH
N
CH
3
4
5
6
1
2
O
NH
2
C
N
H
C
CH
HN
CH
3
4
5
6
1
2
O
O
C
N
H
C
CH
HN
C–H
3
3
4
5
6
1
2
O
O
3
2
4
1
HOH
2
C
5
H
H
H
OH
H
OH
OH
O
3
2
4
1
HOH
2
C
5
H
H
H
OH
H
OH
Ribose
Deoxyribose
O
–
O
–
O
–
O
P
A
● Figure 1-1 (A) Structure of the biochemical components of DNA and RNA (purines, pyrimidines, sugars, and phos-
phate). (continued )
LWBK771-c01_p1-8.qxd 9/29/10 6:48PM Page 1 aptara
2
CHAPTER 1
Levels of DNA Packaging (Figure 1-2)
A. DOUBLE HELIX DNA
1.
The DNA molecule is two complementary polynucleotide chains (or DNA strands)
arranged as a double helix which are held together by hydrogen bonding between
laterally opposed base pairs (bps).
2.
DNA can adopt different helical structures which include: A-DNA and B-DNA
which are right-handed helices with 11 and 10 bps per turn, respectively, and Z-
DNA which is a left-handed helix with 12 bps per turn.
3.
In humans, most of the DNA is in the B-DNA form under physiological conditions.
Adenine
Cytosine
NH
2
H
H
N
N
N
N
NH
2
O
N
H
H
N
O
O
–
P
O
O
CH
2
O
O
O
–
P
O
O
CH
2
O
Thymine
O
O
H
H
3
C
N H
N
5' end
3' end
Guanine
O
H
H
NH
2
N
N
N
N
O
O
–
P
O
O
CH
2
O
O
O
–
P
O
O
CH
2
O
O
Phosphodiester
bond
B
● Figure 1-1 (Continued) (B) Diagram of a DNA polynucleotide chain. The biochemical components (purines, pyrim-
idines, sugar, and phosphate) form a polynucleotide chain through a 3
,5-phosphodiester bond. If a piece of DNA con-
tains 20% thymine, how much guanine does the piece of DNA contain? If the piece of DNA contains 20% thymine,
then the piece of DNA will contain 20% adenine which equals 40% (thymine and adenine). The remaining 60% will
consist of cytosine and guanine which are paired. Consequently, the piece of DNA will contain 30% guanine. A good
mnemonic to remember which nitrogenous bases are purines is Pure As Gold (Adenine and Guanine are Purines).
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