Table of Contents
Why is it structurally important that a purine base always pair with a pyrimidine base in the DNA double helix?
For the two strands of the double helix to fit neatly, a pyrimidine must always be paired with a purine. The second thing you should notice in Figure 15.2. 3 is that the correct pairing enables formation of three instances of hydrogen bonding between guanine and cytosine and two between adenine and thymine.
Do purines always pair up with a pyrimidine?
Because purines always bind with pyrimidines – known as complementary pairing – the ratio of the two will always be constant within a DNA molecule. There are two main types of purine: Adenine and Guanine. Both of these occur in both DNA and RNA.
Why do purines not pair with purines?
Purines are large nitrogenous bases due to two nitrogen rings in their structure. Two complementary strands of the DNA can accommodate only three nitrogen rings between them. Thus, purine-purine cannot pair with each other due to the unavailability of the required space to bond together in the DNA double helix.
How do purines and pyrimidines pair?
Purines always bond with pyrimidines via hydrogen bonds following the Chargaff rule in dsDNA, more specifically each bond follows Watson-Crick base pairing rules. Therefore adenine specifically bonds to thymine forming two hydrogen bonds, whereas guanine forms three hydrogen bonds with Cytosine.
What is the difference between purine and pyrimidine?
Adenine and guanine are the two purines and cytosine, thymine and uracil are the three pyrimidines. The main difference between purines and pyrimidines is that purines contain a sixmembered nitrogencontaining ring fused to an imidazole ring whereas pyrimidines contain only a sixmembered nitrogencontaining ring.
Why is purine important in DNA synthesis?
Purine nucleotides are involved in many cellular functions as components of DNA and RNA, as sources of energy, as enzyme cofactors in metabolic pathways, and as components of signal transduction. PRPP is also used in pyrimidine and pyridine nucleotide synthesis and in salvage of preformed purine bases.
Do pyrimidines form covalent bonds with purines?
Purines form covalent bonds with pyrimidines. Purines consist of a two-ring structure. Purines form hydrogen bonds with pyrimidines.
What does purine pair with?
A with T: the purine adenine (A) always pairs with the pyrimidine thymine (T) C with G: the pyrimidine cytosine (C) always pairs with the purine guanine (G)
What is advantage of purine base pair with another purine?
Dictated by specific hydrogen bonding patterns ,base pairs between Guanine (G) – Cytosine (C) and Adenine (A) – Thymine (T) , allow the DNA helix to maintain a regular helical structure.
How do purines and pyrimidines differ?
What characteristic makes purines and pyrimidine heterocyclic?
A purine is a heterocyclic aromatic organic compound containing 4 nitrogen atoms. It contains two carbon rings, and is made of a pyrimidine ring fused to an imidazole ring. A pyrimidine is a heterocyclic aromatic organic compound containing 2 nitrogen atoms. It contains only one carbon ring.