Complete the passage describing nitrogenous base pairs in a DNA molecule. In a DNA molecule, the nitrogenous bases are oriented toward the of two adjacent nucleotides on the nitrogenous bases. of the double helix. Base pairs consist Base pairs are held together by bonds between
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Step 1: The nitrogenous bases are oriented toward the **interior** of the double helix. Show more…
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The following excerpts are from Watson and Crick's description of the structure of DNA. "The novel feature of the structure is the manner in which the two chains are held together by the purine and pyrimidine bases. The planes of the bases are perpendicular to the fibre axis. They are joined together in pairs, a single base from one chain being hydrogen-bonded to a single base from the other chain so that the two lie side by side with identical $z-$co-ordinates. One of the pair must be a purine and the other a pyrimidine for bonding to occur." "It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material." According to the description, how are the bases joined together?
5. These bases are of two different types of molecules: purines and pyrimidines. Purines have rings in their structure, and pyrimidines have rings in their structure. 6. The two bases that are purines are and . These bases are comprised of rings. 7. The two bases that are pyrimidines are and . These bases are comprised of rings. 8. Based on this information, scientist could predict that the base pairs with and the base pairs with in the formation of the DNA molecule. This is called complementary base pairs. Thus one strand of DNA is complementary to the other strand (opposite/matching). 9. The bases are paired by bonds along the axis of the molecule.
Sri K.
BIO Base Pairing in DNA, I. The two sides of the DNA double helix are connected by pairs of bases (adenine, thymine, cytosine, and guanine). Because of the geometric shape of these molecules, adenine bonds with thymine and cytosine bonds with guanine. Figure E21.23 shows the thymine-adenine bond. Each charge shown is $\pm e,$ and the $\mathrm{H}-\mathrm{N}$ distance is 0.110 $\mathrm{nm} .$ (a) Calculate the net force that thymine exerts on adenine. Is it attractive or repulsive? To keep the calculations fairly simple, yet reasonable, consider only the forces due to the $\mathrm{O}-\mathrm{H}-\mathrm{N}$ and the $\mathrm{N}-\mathrm{H}-\mathrm{N}$ combinations, assuming that these two combinations are parallel to each other. Remember, however, that in the $\mathrm{O}-\mathrm{H}-\mathrm{N}$ set, the $\mathrm{O}^{-}$ exerts a force on both the $\mathrm{H}^{+}$ and the $\mathrm{N}^{-}$ and likewise along the $\mathrm{N}-\mathrm{H}-\mathrm{N}$ set. (b) Calculate the force on the electron in the hydrogen atom, which is 0.0529 nm from the proton. Then compare the strength of the bonding force of the electron in hydrogen with the bonding force of the adenine-thymine molecules.
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