Where are there weak bonds in dna molecules

Hydrogen bond acceptors are electronegative atoms with at least one lone pair of electrons. Also notice that potential hydrogen bond donors and acceptors close to the sugar R group are ignored in the image above. This is because those parts of the nitrogenous base close to the sugar-phosphate backbone will be unavailable for hydrogen bonding with the other base in the pair.

Let's examine a single guanine residue to identify potential hydrogen bond donors and acceptors. Guanine will be highlighted in yellow , and the attached sugar and phosphate in the backbone will blink purple. Keeping in mind the point of sugar attachment, we can identify guanine's hydrogen bond donors and acceptors that are available to interact with a paired nitrogenous base. Locate these parts of the molecule yourself, then click the button below to see the relevant atoms blink yellow.

Which of the following statements best describes the hydrogen bonding potential in guanine? Guanine has 3 H-bond donors. Guanine has 3 H-bond acceptors. Guanine has 2 H-bond acceptors and 1 H-bond donor. Guanine has 1 H-bond acceptor and 1 H-bond donor. Guanine has 1 H-bond acceptor and 2 H-bond donors.

Can you find one H-bond donor and 2 H-bond acceptors in cytosine? Examine the molecule yourself, then click the button below to see the relevant atoms blink green. Guanine and cytosine make up a nitrogenous base pair because their available hydrogen bond donors and hydrogen bond acceptors pair with each other in space. Guanine and cytosine are said to be complementary to each other. This is shown in the image below, with hydrogen bonds illustrated by dotted lines.

The button below the image highlights the hydrogen bonds between guanine and cytosine in a DNA double helix. Adenine and thymine similarly pair via hydrogen bond donors and acceptors; however an AT base pair has only two hydrogen bonds between the bases.

Examine the image and click the button below to explore hydrogen bonding in an AT base pair. Hydrogen bonds are weak, noncovalent interactions, but the large number of hydrogen bonds between complementary base pairs in a DNA double helix combine to provide great stability for the structure. The four bases in DNA's alphabet are:. Watson and Crick discovered that DNA had two sides, or strands, and that these strands were twisted together like a twisted ladder -- the double helix.

The sides of the ladder comprise the sugar-phosphate portions of adjacent nucleotides bonded together. The phosphate of one nucleotide is covalently bound a bond in which one or more pairs of electrons are shared by two atoms to the sugar of the next nucleotide. The hydrogen bonds between phosphates cause the DNA strand to twist. The nitrogenous bases point inward on the ladder and form pairs with bases on the other side, like rungs.

Each base pair is formed from two complementary nucleotides purine with pyrimidine bound together by hydrogen bonds. The base pairs in DNA are adenine with thymine and cytosine with guanine. A hydrogen bond is a weak chemical bond that occurs between hydrogen atoms and more electronegative atoms, like oxygen, nitrogen and fluorine.

The participating atoms can be located on the same molecule adjacent nucleotides or on different molecules adjacent nucleotides on different DNA strands. Hydrogen bonds do not involve the exchange or sharing of electrons like covalent and ionic bonds.

The weak attraction is like that between the opposite poles of a magnet. Hydrogen bonds occur over short distances and can be easily formed and broken. They can also stabilize a molecule.

Base-pairing takes place between a purine and pyrimidine: namely, A pairs with T, and G pairs with C. In other words, adenine and thymine are complementary base pairs, and cytosine and guanine are also complementary base pairs. Adenine and thymine are connected by two hydrogen bonds, and cytosine and guanine are connected by three hydrogen bonds. The diameter of the DNA double helix is uniform throughout because a purine two rings always pairs with a pyrimidine one ring and their combined lengths are always equal.

Figure 9. There is a second nucleic acid in all cells called ribonucleic acid, or RNA. Each of the nucleotides in RNA is made up of a nitrogenous base, a five-carbon sugar, and a phosphate group.

In the case of RNA, the five-carbon sugar is ribose, not deoxyribose. RNA nucleotides contain the nitrogenous bases adenine, cytosine, and guanine. Molecular biologists have named several kinds of RNA on the basis of their function. For this reason, the DNA is protected and packaged in very specific ways. In addition, DNA molecules can be very long.

Stretched end-to-end, the DNA molecules in a single human cell would come to a length of about 2 meters. Thus, the DNA for a cell must be packaged in a very ordered way to fit and function within a structure the cell that is not visible to the naked eye. The chromosomes of prokaryotes are much simpler than those of eukaryotes in many of their features Figure 9.

Most prokaryotes contain a single, circular chromosome that is found in an area in the cytoplasm called the nucleoid. The size of the genome in one of the most well-studied prokaryotes, Escherichia coli, is 4. So how does this fit inside a small bacterial cell? The DNA is twisted beyond the double helix in what is known as supercoiling.

Some proteins are known to be involved in the supercoiling; other proteins and enzymes help in maintaining the supercoiled structure. Eukaryotes, whose chromosomes each consist of a linear DNA molecule, employ a different type of packing strategy to fit their DNA inside the nucleus. At the most basic level, DNA is wrapped around proteins known as histones to form structures called nucleosomes.