6
FRIEDHELM HILDEBRANDT
Primary structure of DNA
Figure 2D: A triphosphate residue, bound to the 5' -OH of the nucleotide
adenosine-5' -triphosphate, interacts with the 3' -OH of the nucleic acid
and engages in a phosphodiester bond after cleavage of a pyrophosphate,
which contributes the energy required for the reaction. The result of the
reaction is shown in Figure 2C. Nucleic acids are synthesized starting
from the 5' end proceeding towards their 3' end. As a convention, nucleotide
sequences are written from their 5' end on the left to the 3' end to the right
(Figure 2C). In double-stranded DNA this rule applies for the strand written
in the upper row.
Secondary structure of DNA
N aturally occurring DN A is double stranded. J. W atson and F. Crick in 1953
provided the model for DNA of a right handed double helix containing two
anti-parallel strands, meaning that the strands run 5' to 3' in opposite directions (Figure 3A). Sugars connected with phosphodiester bondsform the
back hone for the structure, which resembles 2 intertwined spiral staircases.
Base pairing occurs between complementary bases. C and G form 3 hydrogen bonds, whereas A and T only 2 hydrogen bonds (see Figure 3A). Since
the glycosidic bonds between the sugars and the complementary bases are
not exactly opposite each other, the double helix exhibits a major and a
minor groove (Figure 3B). DNA binding proteins, such as restriction enzymes and transcription factors, recognize specific bases mainly via interaction with the major groove (Figure 3C).
The most common conformation of the double helix in aqueous solution
is so called B-DNA (Figure 3D). There are 10 base pairs per turn. Since the
glycosidic bonds of the bases can rotate freely, the double helix can undergo
conformational changes. In its A-Form the major groove is shortened. In
the rarely occurring Z-Form the double helix has switched to a left-handed
helix (Figure 3D). The conformation of DNA is dependent on its state of
hydration and its nucleotide sequence. The different conformational states
most likely have a regulatory function. Scanning tunneling microscopy has
allowed a direct view of the DNA double helix (Figure 3E).
FRIEDHELM HILDEBRANDT
Primary structure of DNA
Figure 2D: A triphosphate residue, bound to the 5' -OH of the nucleotide
adenosine-5' -triphosphate, interacts with the 3' -OH of the nucleic acid
and engages in a phosphodiester bond after cleavage of a pyrophosphate,
which contributes the energy required for the reaction. The result of the
reaction is shown in Figure 2C. Nucleic acids are synthesized starting
from the 5' end proceeding towards their 3' end. As a convention, nucleotide
sequences are written from their 5' end on the left to the 3' end to the right
(Figure 2C). In double-stranded DNA this rule applies for the strand written
in the upper row.
Secondary structure of DNA
N aturally occurring DN A is double stranded. J. W atson and F. Crick in 1953
provided the model for DNA of a right handed double helix containing two
anti-parallel strands, meaning that the strands run 5' to 3' in opposite directions (Figure 3A). Sugars connected with phosphodiester bondsform the
back hone for the structure, which resembles 2 intertwined spiral staircases.
Base pairing occurs between complementary bases. C and G form 3 hydrogen bonds, whereas A and T only 2 hydrogen bonds (see Figure 3A). Since
the glycosidic bonds between the sugars and the complementary bases are
not exactly opposite each other, the double helix exhibits a major and a
minor groove (Figure 3B). DNA binding proteins, such as restriction enzymes and transcription factors, recognize specific bases mainly via interaction with the major groove (Figure 3C).
The most common conformation of the double helix in aqueous solution
is so called B-DNA (Figure 3D). There are 10 base pairs per turn. Since the
glycosidic bonds of the bases can rotate freely, the double helix can undergo
conformational changes. In its A-Form the major groove is shortened. In
the rarely occurring Z-Form the double helix has switched to a left-handed
helix (Figure 3D). The conformation of DNA is dependent on its state of
hydration and its nucleotide sequence. The different conformational states
most likely have a regulatory function. Scanning tunneling microscopy has
allowed a direct view of the DNA double helix (Figure 3E).