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DNA can be twisted like a rope in a process called DNA supercoiling. With DNA in its "relaxed" state, a strand usually circles the axis of the double helix once every 10.4 base pairs, but if the DNA is twisted the strands become more tightly or more loosely wound. [43]
Deoxyribonucleic acid (DNA) is a nucleic acid containing the genetic instructions used in the development and functioning of all known living organisms. The chemical DNA was discovered in 1869, but its role in genetic inheritance was not demonstrated until 1943. The DNA segments that carry this genetic information are called genes.
A single-stranded non-circular DNA molecule has two non-identical ends, the 3' end and the 5' end (usually pronounced "three prime end" and "five prime end"). The numbers refer to the numbering of carbon atoms in the deoxyribose, which is a sugar forming an important part of the backbone of the DNA molecule. In the backbone of DNA the 5' carbon ...
DNA for Beginners, republished as DNA: A Graphic Guide to the Molecule that Shook the World, is a 1983 graphic study guide to DNA written by Professor Israel Rosenfield from the City University of New York with Professor Edward Ziff from the New York University School of Medicine, and illustrated by Borin Van Loon.
The two base-pair complementary chains of the DNA molecule allow replication of the genetic instructions. The "specific pairing" is a key feature of the Watson and Crick model of DNA, the pairing of nucleotide subunits. [5] In DNA, the amount of guanine is equal to cytosine and the amount of adenine is equal to thymine. The A:T and C:G pairs ...
Selected portions of the DNA nucleotide sequence are copied into a corresponding RNA nucleotide sequence, which either encodes a protein (if it is an mRNA) or forms a 'structural' RNA, such as a transfer RNA (tRNA) or ribosomal RNA (rRNA) molecule. Each region of the DNA helix that produces a functional RNA molecule constitutes a gene. [15]
The 5′-end (pronounced "five prime end") designates the end of the DNA or RNA strand that has the fifth carbon in the sugar-ring of the deoxyribose or ribose at its terminus. A phosphate group attached to the 5′-end permits ligation of two nucleotides , i.e., the covalent binding of a 5′-phosphate to the 3′-hydroxyl group of another ...
In DNA double helix, the two strands of DNA are held together by hydrogen bonds. The nucleotides on one strand base pairs with the nucleotide on the other strand. The secondary structure is responsible for the shape that the nucleic acid assumes. The bases in the DNA are classified as purines and pyrimidines. The purines are adenine and guanine ...