Why does purine always pair with pyrimidine?

These nucleotides are complementary —their shape allows them to bond together with hydrogen bonds. In the C-G pair, the purine (guanine) has three binding sites, and so does the pyrimidine (cytosine). The hydrogen bonding between complementary bases is what holds the two strands of DNA together.

Accordingly, why does a pyrimidine only bond with a purine?

The molecular structure of both pyrimidines and purines allow them to only be able to bond with each other and not within the group. Thymine (pyrimidine)and adenine (purine) both have two atoms that can either provide a H bond or receive it.

Similarly, do purines always pair with pyrimidines? 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 pair with pyrimidines in the DNA ladder?

According to the base-pair rule, purines bond with pyrimidines because adenine will only bond with thymine, and guanine will only bond with cytosine due to opposing poles. Hydrogen bonds hold them together.

Which amino acid is required for both purine and pyrimidine synthesis?

Biosynthesis of purine and pyrimidine nucleotides requires carbon dioxide and the amide nitrogen of glutamine. Both use an amino acid “nucleus”—glycine in purine biosynthesis and aspartate in pyrimidine biosynthesis. Both use PRPP as the source of ribose 1-phosphate.

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