How many amino acid units do these atoms come from? Why are these units planar?

Question

Accepted Answer

Hi, everybody. Here's our next problem. Consider the following protein chain and we have a protein chain drawn several amino acids. It's drawn in a format where we mainly just see the backbone of the amino backbone structure of the amino acids with the R groups attached written just as a group of letters. So we're focusing on the backbone structure here. Our question says how many amino acids make the atoms in a cleaner unit? Why are the units cleaner? A only one amino acid makes the atoms in the planar units? The units are planar because the double bond from the carbonel group makes rotation around this bond. Restricted B two amino acids make the atoms in the planar units. Their planar because the electrons are delocalized throughout the sea double bond O and CN bonds restricting rotation around that bond. C only one amino acid makes the atoms in the planar units. The units are planar because the amino acid side chains or stick the rotation of the bonds around the central carbon atom or D two amino acids make the atoms in the planar units. Units are planar because the amid bond CN is from two amino acids restricting rotation around that bond. When we think about planar units, which type of bonds are planar. We think about double bonds because double bonds such as the C double bond to the O will have a trigonal planar geometry. All of the atoms in that bond will be within the same plane and rotation will be restricted around that double bond. So that would tempt us to lead. Look at answer a only one amino acid. However, we need to recognize that I highlighted read here with the C double bond to an O next to an NH group that is essentially an amid functional group. I am it in here. And the result is you can have with an amid, you have de localization of electrons because you can have while you have this carbon carbon bonded to an NH group that has a resonance structure of a carbon with a single bond to an O minus and then a double bond to the nitrogen to the NH which now has a positive charge on the nitrogen. So you see the electrons being localized delocalized over the co and CN bonds. So each of these bonds will have a partial double bond character. And so therefore, rotation around those bonds will be restricted. So both of them. So our answer block should be B two amino acids make the atoms in the planar units. They're planar because the electrons are delocalized through the co and CN bonds which restricts rotation. So choice A is incorrect because we have partial double bond characteristics on both the co and the CN bonds. Choice C also incorrect since it has only one amino acid and amino acid side chains will not restrict the rotation of the bonds. Since the amino acid side chains are single bonded to the carbon. And therefore, those alpha carbons have a tetrahedral geometry around them with free rotation around those bonds. And choice D correctly says two, but it says the units are planar because the amid bond is from two amino acids that wouldn't restrict rotation. As long as it's a single bond, they can have rotation. So choice D is incorrect. Once the granite, correct answer is choice be there that it's two amino acids making of the planar units or atoms from them. Since the electrons are delocalized, those co and CN bonds. See you in the next video.

How many amino acid units do these atoms come from? Why are these units planar?

Verified video answer for a similar problem:

Key Concepts

Amino Acids

Planarity of Amino Acids

Peptide Bonds