Double helix7/13/2023 The linker in the polymer is marked in orange. (c) Representative structures in different phases: random coils ( R), random coils with flickering helical ordering ( R *), globules ( G), globules with local helical ordering ( G *), compact structures ( C 1), compact structures with local helical ordering ( C 2), two-helix bundles ( H 2), and double-helix structures ( D H 1). Colored regions stand for structural phases. The dotted lines represent the transition temperatures. (a) Varying the torsion stiffness k τ and the temperature T at a fixed bending stiffness k θ = 10. The structure of A-DNA is more similar to B-DNA whereas Z-DNA forms a left-handed helix and also does not show many differences between major and minor grooves.Phase diagrams for the self-folding of single semiflexible polymers of length N = 30 with reference angles θ 0 = 105 ° and τ 0 = 50 °. However, two other much rarer confirmations of DNA are also present in nature Z-DNA and A-DNA. The enzyme plays a significant role in DNA damage repair and the process of transcription.Īlternative DNA structures: B-DNA, or Watson and Crick model is the most common structure of DNA. Helicase breaks the hydrogen bonds between the paired nucleotides and remodels the structure of DNA. An enzyme, helicase is used for unzipping. The replication needs unwinding or unzipping of the double helix structure so that the nucleotide sequences can be replicated. The Unwinding Enzyme: The DNA is replicated or copied by the cell to pass it on to the next generation. However other proteins interact with the minor groove and do not require sequence-specificity. Certain proteins that need to interact with nucleotides, such as transcription factors or DNA replication enzymes, prefer to bind to the major groove of the DNA. The major groove forms when they are closer whereas when they are apart from each other, they form a minor groove. Major and Minor Grooves: The double helix structure of DNA contains a backbone of the two strands, which is closer together on one side of the helix than the other. The phosphate group is attached to the 5th carbon thus it is called 5’ whereas the OH group is attached to the third carbon and is known as 3’. And the other strand ends on a hydroxyl group. Organisms propagate the sequence of DNA among generations, therefore, for the continuation of life, the DNA sequence is essential.Īntiparallel Orientation: Both strands of DNA are antiparallel to each other, which means that one strand ends on a phosphate group at the end of a particular molecule. Therefore the genetic information carried out by these nucleotides is also unique in each organism. Genetic Code: All the organisms have a different sequence of nucleotides. Therefore, these strands are called complementary to each other. The guanine and cytosine are connected with three hydrogen bonds whereas adenine and thymine have two hydrogen bonds. For example, adenine always pairs up with thymine, and guanine pairs with cytosine. The DNA strands occur in the outside of the helix, and the nitrogenous bases occur at the core of the helix.Ĭomplementary Base Pairing: The hydrogen bonding between the nucleotides always occurs in a particular manner. Almost always the helix turns in a right-handed direction. The helix turns once every ten nucleotides. Helix Directionality: The DNA molecule is made up of two strands that form a helix by twisting around each other. Watson/Crick model of the DNA double helix has some important features including: He added the name of Rosalind Franklin to the plaque and recognize his important role in the discovery. Thus, they proposed a model that was considered accurate for several decades.Īfter completing the research Crick announced in their local pub in Cambridge that he and Watson had discovered “the secret to life.” To commemorate the occasion, the pub named The Eagle erected a plaque, which was once modified by a member of the public. They carefully construct a series of cardboard models and finally form a structure that made sense. Watson and Crick use all the evidence as well as X-ray crystallography data collected by Rosalind Franklin to derive their model. A lot of research had already been carried out by scientists on the composition of DNA before the publication of the double helix structure.įor example, Chargaff’s rules about the ratio of purines and pyrimidines were already discovered. Wilkins has also an important role in the research thus his biography is also titled, “The Third Man of the Double Helix”. Both the scientists along with Maurice Wilkins were awarded by Nobel Prize for their research. It was first discovered by biologist James Watson and physicist Francis Crick in the 1950s. In the field of biology, the discovery of the structure of DNA is one of the most significant events.
0 Comments
Leave a Reply. |