Why are there two hydrogen bonds between adenine and thymine but three hydrogen bonds between cytosine and guanine?

Asked By: Odis Pessego | Last Updated: 27th January, 2020
Category: science genetics
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Adenine pairs with thymine with 2 hydrogen bonds. Guanine pairs with cytosine with 3 hydrogen bonds. This creates a difference in strength between the two sets of Watson and Crick bases. The higher the temperature at which DNA denatures the more guanine and cytosine base pairs are present.

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In respect to this, why does cytosine and guanine have 3 hydrogen bonds?

Guanine and Cytosine Base pair has three hydrogen bonds,because the exocyclic NH2 at C2 on Guanine lies opposite to,and can hydrogen bond with,a carbonyl at C2 on Cytosine.

Similarly, why is there hydrogen bonds between each nitrogen base? Base Pairing in DNA The nitrogen bases form the double-strand of DNA through weak hydrogen bonds. The nitrogen bases, however, have specific shapes and hydrogen bond properties so that guanine and cytosine only bond with each other, while adenine and thymine also bond exclusively.

Keeping this in consideration, how many hydrogen bonds are possible between adenine and guanine?

Two hydrogen bonds

How many hydrogen bonds are found between CG?

The A-T pair forms two hydrogen bonds. The C-G pair forms three. The hydrogen bonding between complementary bases holds the two strands of DNA together. Hydrogen bonds are not chemical bonds.

39 Related Question Answers Found

Why can't AC and GT pairs form?

The arrangements of atoms in the four kinds of nitrogenous bases is such that two hydrogen bonds are formed automatically when A and T are present on opposite DNA strands, and three are formed when G and C come together this way. A-C or G-T pairs would not be able to form similar sets of hydro- gen bonds.

Which hydrogen bond is strongest?

Thus, on a per bond basis, HF H bonding is strongest. However, as water has two H atoms, each molecule can form two H bonds so on a per molecule basis, water H bonding is strongest (this is evidenced by the boiling points of the three substances; NH3 < HF < H2O.)

Why are hydrogen bonds in DNA important?

Hydrogen bonding is important because it is crucial to all life on Earth. Here are three reasons why hydrogen bonding is important. DNA has a double-helix structure because hydrogen bonds hold together the base pairs in the middle. Without hydrogen bonds, DNA would have to exist as a different structure.

Why are hydrogen bonds 180 degrees?


However, they are particularly strong interactions and are usually referred to as hydrogen bonds. Also note the O-H-O bond angle of 180°. This occurs because there are no two mutually repelling pairs of electrons around the hydrogen atom, i) the O-H bond pair and ii) the lone pair involved in the hydrogen bond.

Which base has largest hydrogen bonding possibility?

Expln:- In the given choice, Guanine has the largest hydrogen bonding possibility, because it contains the highest number of electron donor sites.

How many hydrogen bonds are in this strand of DNA Aggctcg?

An Adenine and Thymine pair forms two hydrogen bonds

How do you determine the number of hydrogen bonds in DNA?

The rules for base-pairing in DNA are as follows: adenine pairs to thymine and cytosine pairs to guanine. If there are 200 adenines in the DNA, it follows there must also be 200 thymines. Each adenine and thymine are held together by a hydrogen bond. Therefore, there must be 200 hydrogen bonds between them.

What happens if adenine bonds with guanine?

The chemistry of the nitrogenous bases is really the key to the function of DNA. It allows something called complementary base pairing. You see, cytosine can form three hydrogen bonds with guanine, and adenine can form two hydrogen bonds with thymine. Or, more simply, C bonds with G and A bonds with T.

Why does adenine and thymine have 2 hydrogen bonds?


DNA. In the DNA helix, the bases: adenine, cytosine, thymine and guanine are each linked with their complementary base by hydrogen bonding. Adenine pairs with thymine with 2 hydrogen bonds. This difference in strength is because of the difference in the number of hydrogen bonds.

Why does adenine and thymine pair together?

Adenine and Thymine also have a favorable configuration for their bonds. They both have to -OH/-NH groups which can form hydrogen bridges. When one pairs Adenine with Cytosine, the various groups are in each others way. For them to bond with each other would be chemically unfavorable.

Why is uracil complementary only to adenine?

The first three are the same as those found in DNA, but in RNA thymine is replaced by uracil as the base complementary to adenine. This base is also a pyrimidine and is very similar to thymine. Uracil is energetically less expensive to produce than thymine, which may account for its use in RNA.

How does adenine guanine thymine uracil and cytosine interact with each other?

Adenine forms two hydrogen bonds with thymine in DNA and two hydrogen bonds with uracil in RNA, while three hydrogen bonds are formed between guanine and cytosine.

Why are hydrogen bonds in DNA weak?

These hydrogen bonds between complementary nucleotides are what keeps the two strands of a DNA helix together. Each base can also form hydrogen bonds with the external environment such as with water. The hydrogen bonding is a weak molecular force, but it is an additive effect that stabilizes the DNA molecule.

What are the two purines?


Purine contains two carbon-nitrogen rings and four nitrogen atoms. Two Purines are Adenine and Guanine. Two Pyrimidines are Thymine and Uracil.

Why do purines and pyrimidines bond?

Pairing of a specific purine to a pyrimidine is due to the structure and properties of these bases. In DNA base pairing, A pairs with T and C with G. Matching base pairs ( purines and pyrimidines ) form hydrogen bonds. A and T have two sites where they form hydrogen bonds to each other.

What are the base pairing rules?

The rules of base pairing (or nucleotide pairing) are:
  • 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)