DNA: Difference between revisions
From Proteopedia
Jump to navigationJump to search
Eran Hodis (talk | contribs) |
Eran Hodis (talk | contribs) |
||
| Line 22: | Line 22: | ||
== Variations on a Theme == | == Variations on a Theme == | ||
[[Image:MotM ABZ.gif |left |thumb| | [[Image:MotM ABZ.gif |left |thumb|250px|Left: A-DNA from [[1ana]], Center: B-helix from [[1bna]], Right: Z-DNA from [[2dcg]]]] | ||
DNA adopts the familiar smooth double helix, termed a B-helix, under the typical conditions found in living cells. An example is shown in the center, exemplified by the crystal structure [[1bna]], shown at the top superimposed over the idealized version of the B-helix. Under other conditions, however, DNA can form other structures, as revealed in two early crystal structures: [[1ana]] on the left and [[2dcg]] on the right. The one on the left, with tipped bases and a deep major groove, is termed A-DNA. It is formed under dehydrating conditions. Also, RNA most often shows this form, because its extra hydroxyl group on the sugar gets in the way, making the B-form unstable (look, for instance, at the A-helical structure of transfer RNA shown in a previous Molecule of the Month). The form on the right, which winds in the opposite direction from A-DNA and B- DNA, is termed Z-DNA. It is found under high salt conditions and requires a special type of base sequence, with many alternating cytosine-guanine and guanine-cytosine base pairs. | DNA adopts the familiar smooth double helix, termed a B-helix, under the typical conditions found in living cells. An example is shown in the center, exemplified by the crystal structure [[1bna]], shown at the top superimposed over the idealized version of the B-helix. Under other conditions, however, DNA can form other structures, as revealed in two early crystal structures: [[1ana]] on the left and [[2dcg]] on the right. The one on the left, with tipped bases and a deep major groove, is termed A-DNA. It is formed under dehydrating conditions. Also, RNA most often shows this form, because its extra hydroxyl group on the sugar gets in the way, making the B-form unstable (look, for instance, at the A-helical structure of transfer RNA shown in a previous Molecule of the Month). The form on the right, which winds in the opposite direction from A-DNA and B- DNA, is termed Z-DNA. It is found under high salt conditions and requires a special type of base sequence, with many alternating cytosine-guanine and guanine-cytosine base pairs. | ||
