What is a Double Helix?
A double helix is a geometrical shape consisting of two helices around the same axis. A helix is a twisting spiral shape, like a spring. The two helices in a double helix are congruent, meaning that they are the same in every dimension, though in different positions around the axis. A double helix may be either right-handed or left-handed, depending on whether it coils clockwise or counter-clockwise, respectively. The double helix is probably best known as the shape of deoxyribonucleic acid (DNA), the material that carries genetic information in the body. The DNA double helix is right-handed and consists of two strands or backbones of phosphate and sugar joined by base pairs of the nucleotides adenine, thymine, guanine, and cytosine, often abbreviated A, T, G, and C. Adenine always joins with thymine, and guanine always joins with cytosine, so knowing the bases on one side of the double helix reveals those on the other side. These four nucleotides are responsible for encoding all of th
What do the letters A, T, C, and G stand for? Find out at Discovering DNA’s Double Helix. • Scientists are exploring the DNA of many organisms, including humans! Explain what the human genome is. Why do scientists want to study it? See the Human Genome Project, and click the three different questions. • Scientists also study the DNA of animals, especially those that are endangered. Check out Around the World With DNA to see how scientists study animal DNA in different habitats across the globe. Compare and contrast the St. Vincent parrot and the pacu. Where does each animal live? Why is it endangered? How do scientists collect DNA for the animal? How do they use DNA to help protect the animal? • In 1997, a special sheep named Dolly was introduced to the world. She was the first animal “clone” — an exact genetic copy of another sheep. Name two reasons why scientists would want to clone animals. Learn All About Cloning to find the answer. (Hint: be sure to click the little sheep, “Why Cl
