DNA double helix
In the early 1950s, Rosalind Franklin and Maurice Wilkens used X-ray diffraction to show that DNA has a double helix structure. Two sugar-phosphate backbones wrap around one another held together by hydrogen bonding between specific base groups attached to the sugar groups of the backbone.
Instructions
1. Draw an undulating vertical line with three complete wave cycles on a blank piece of paper. The line should resemble a sine wave rotated 90 degrees.
2. Draw a second undulating line beginning about 3 centimeters above and to the left of the first undulating line. Ensure that the waves of the new line are on a different cycle than the first line so the two lines intersect at regular intervals. These two lines represent the sugar phosphate backbone of the DNA molecule.
3. Draw a small rectangle coming off the first sugar-phosphate backbone towards the second sugar-phosphate backbone. The rectangle should be drawn at the top of the first open segment of the sugar-phosphate backbone and it should transverse 2/3 of the distance to the second backbone. Draw a convex point instead of a straight line for the edge of the rectangle closest to the second backbone. Label this base thymine.
4. Draw a second small rectangle bridging the remaining distance between the second sugar-phosphate backbone and the convex point on the thymine base. The edge of the new base closest to the thymine should be represented by a concave point. Label this base adenine. Together these represent the first base pair for your DNA helix.
5. Draw another rectangle coming off the first sugar-phosphate backbone directly under the first base pair. This rectangle should transverse only 1/3 of the distance to the second backbone. Draw a concave arch in place of the edge of the rectangle closest to the second sugar-phosphate backbone. Label this base cytosine.
6. Draw another small rectangle bridging the remaining distance between the second sugar-phosphate backbone and the concave arch on the cytosine base. The edge of the new base that is closest to the cytosine should be represented by a concave point. Label this base guanine. Together these represent the second base pair for your DNA helix.
7. Continue going down the double helix drawing base pairs. Always draw thymine paired with adenine and guanine paired with cytosine. Other than having the correct pairs, the bases can go in any order along the double helix.
Tags: sugar-phosphate backbone, double helix, Label this, Label this base, second sugar-phosphate