Why does dna helix twist

Featured Content. Introduction to Genomics. Polygenic Risk Scores. Two types of base pairing occur: nucleotide A pairs with T, and nucleotide C pairs with G.

Further Exploration Concept Links for further exploration helicase phosphate backbone nucleic acid DNA phosphate backbone replication.

Related Concepts 6. You have authorized LearnCasting of your reading list in Scitable. The nitrogenous bases that comprise the steps of the twisted staircase are held together by hydrogen bonds. Adenine is bonded with thymine A-T and guanine pairs with cytosine G-C. These nitrogenous bases are hydrophobic, meaning that they lack an affinity for water.

Since the cell cytoplasm and cytosol contain water-based liquids, the nitrogenous bases want to avoid contact with cell fluids. The sugar and phosphate molecules that form the sugar-phosphate backbone of the molecule are hydrophilic, which means they are water-loving and have an affinity for water.

DNA is arranged such that the phosphate and the sugar backbone are on the outside and in contact with fluid, while the nitrogenous bases are in the inner portion of the molecule. In order to further prevent the nitrogenous bases from coming into contact with cell fluid, the molecule twists to reduce space between the nitrogenous bases and the phosphate and sugar strands.

The fact that the two DNA strands that form the double helix are anti-parallel helps to twist the molecule as well. Anti-parallel means that the DNA strands run in opposite directions, ensuring that the strands fit tightly together. This reduces the potential for fluid to seep between the bases. The double-helix shape allows for DNA replication and protein synthesis to occur. In DNA replication, the double helix unwinds and each separated strand is used to synthesize a new strand.

As the new strands form, bases are paired together until two double-helix DNA molecules are formed from a single double-helix DNA molecule. DNA replication is required for the processes of mitosis and meiosis to occur. The messenger RNA molecule is then translated to produce proteins.

RNA is also a nucleic acid but contains the base uracil instead of thymine. In transcription, guanine pairs with cytosine and adenine pairs with uracil to form the RNA transcript.

DNA is a large molecule built from smaller molecules of three different chemical ingredients: sugar, phosphate and nitrogenous bases. The sugar and phosphate are located on the outer edges of the DNA molecule, with the bases arranged between them like the rungs of a ladder. Given that the fluids in our cells are water-based, this structure makes sense: sugar and phosphate are both hydrophilic, or water-loving, while the bases are hydrophobic, or water-fearing.

Now, instead of a ladder, picture a twisted rope. The twists bring strands of the rope close together, leaving little space between them. The DNA molecule similarly twists to shrink the spaces between the hydrophobic bases on the inside. The spiral shape discourages water from flowing between them, and at the same time leaves room for the atoms of each chemical ingredient to fit without overlapping or interfering.