You are participating in a study group preparing for an upcoming genetics exam, and one member of the group proposes that each of you draw the structure of two DNA nucleotides joined in a single strand. The figures are drawn and exchanged for correction. You receive the accompanying diagram to correct: Identify and correct at least five things that are wrong in the depiction of each nucleotide.

Question

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Hi, everyone. Welcome back. Let's look at our next question. It says which of the following statements is incorrect. Regarding the structure of the free nucleotide in DNA Choice a says a nitrogenous base is attached to the one prime carbon. Choice BA Hydroxyl group is attached to the two prime carbon To ac three phosphate groups are attached to the five prime carbon. And choice D the nitrogenous base is attached to the one prime carbon by a covalent bond. So this is asking questions about different groups attached to different carbons in the nucleotide molecule. So the best way to think about that is to recall the structure of those free nucleotides. So I will put that on here. So a chemical structure of free nucleotide that hasn't been added to the chain yet have our five Atom ring here, one oxygen and four carbons, a base attached to one of the carbons hydroxy group. Another carbon sticking up out of the ring with the three phosphate groups attached to it. So let's think about we're asked about different numbered carbons. Let's recall the numbering on these carbons. Here we switch to red to label the carbons So we have our oxy oxygen group at the top of our ring structure here. So going to the right, the first carbon here will be carbon one, then continuing around the ring. We've got the second carbon, third carbon worth carbon. And then the fifth carbon is the one sticking up out of the ring with the phosphate groups attached to it. So we've got our carpets numbered here in red. So let's go back to our answer choices. Remembering that we're looking for the incorrect statement. So if it's a correct description, that's not our answer. So choice A says a nitrogenous base is attached to the one prime carbon. And indeed looking at our molecule, the base is attached to that one prime carbon. This is a true statement. It's correct and therefore not our answer. So we'll cross out choice A To B has a hydroxyl group is attached to the two prime carbon. Well, when we go to our two prime carbon, there is no hydroxyl group, just two hydrogens, the hydroxyl group is further on, on the three prime carbon. So this statement is incorrect and therefore is our answer. So we'll circle that. But to be thorough, we'll move on here. The choice c says three phosphate groups are attached to the five prime carbon and that is correct. They are attached to that carbon that sticks up out of the ring. And of course, as we recall our DNA molecule, its directionality is known as the five prime end and the three prime end. So this is the five prime end uh when it's part of the DNA molecule, when a free nucleotide binds on, of course, two of those phosphates get ejected. And that forms a new phospho dira bond with the three prime carbon of the next space. But this is a true statement. And so not our answer. So we'll cross out to c then finally, choice D says the nitrogenous base is attached at the one prime carbon by a covalent bond. And yes, this is true. As we said, it is attached to the one prime carbon. And that is a covalent bond. In each case, it will be a covalent bond between that carbon and a nucleotide in our base. So that is another true statement and can't be our answer. So again, which of the following statements is incorrect regarding the structure of the free nucleotide and DNA choice B A hydroxyl group is attached to the two prime carbon. See you in the next video.

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Key Concepts

Structure of DNA Nucleotides

Phosphodiester Bond

Antiparallel Orientation