The Double Helix
Mr. Anderson, a renowned biology teacher explains exactly what you need to know about the structure and composition of DNA in a short video |
"THE DOUBLE HELIX" DESCRIBES DNA'S
WINDING STRUCTURE Watson and Crick are credited with the discovery and explanation of the double helical structure that DNA is composed of. As noted on DNA Experiments. However, Charagaff was able to explain the 1:1 ratio of pyramidine and purine bases. Thus the guanine is equal to the amount of cytosine and the amount of adenine is equal to the amount of thymine. STRANDS DNA is made up of two polynucleotide stands wound around each other. The two strands are antiparallel; that is, one strand runs 5′ to 3′ while the other runs 3′ to 5′. The helical turn makes the major groove and the adjacent turns create minor grooves Two DNA strands form a helical spiral, winding around a helix axis in a right-handed spiral. Only one type of DNA is left handed and that is Z-DNA BACKBONE The backbone of DNA is based on a repeated pattern of a sugar group and a phosphate group. The phosphate group is bonded to the 5' carbon atom of one deoxyribose covalently bonded to the 3' carbon of the next. The phosphate group on one nucleotide links to the 3' carbon atom on the sugar of another one. In the process, a molecule of water is lost - another condensation reaction BASES Each sugar is covalently bonded to one of the 4 Bases. Adenine, Guanine, Cytosine, and Thymine The bases are complementary base paired according to Charagaff's findings. Adenine bonded to Thymine with 2 hydrogen bonds. Guanine bonded to Cytosine with 3 hydrogen bonds. The DNA stores information in the infinite sequences of the 4 bases The variable sequence of bases from individual to individual is one source of biological variation. Additional Information:
Early evidence of DNA structure can be credited to Watson and Crick, Maurice Wilkins, and Rosalind Franklin for illustrating the three-dimensional structure of DNA.Watson and Crick were the first to describe DNA as being in a double helix form in their journal, Nature. |