Primary Structure of Nucleic Acids - Video Tutorials & Practice Problems

Primary Structure of Nucleic Acids Concept 1

Hey, everyone. So we're going to say here that the primary structure of a nucleic acid is the sequence of nuclutides attached through Phosphodiester bonds. Now, remember, we said that a nucleotide is made up of 3 important parts. We have our phosphate group, we have our pentose ring, and then we have our nitrogenous base. 2 of these nucleotides can be connected to each other through phosphodiester bonds. When we talk about the primary structure, it's just a chain of these nucleotides connected with multiple phosphodiester bonds. Now here, the phosphodiester bonds themselves, well, these are the bonds of the phosphate group that connects 2 sugars in the primary structure. If we take a look here, we see a phosphate group here, and it's connecting this sugar and this sugar, so that's why we have these purple bonds. Here's this phosphate group here, we have this purple bond and this purple bond because it connects these two sugars. We're gonna say the repeating Phosphate Sugar Phosphate sequence forms the new nucleic acid backbone. So we have our backbone here in the darker blue. And remember, coming off of the sugar itself is our nitrogenous base. These nitrogenous bases could be the same or they could be different. So here we'll say this is nitrogenous base 1, 2, and 3. So just remember that 2 nucleotides can be connected to one another through a phosphodiester bond. When we have a string of nucleotides connected by multiple phosphodiester bonds, this becomes the primary structure of our nucleic acid.

Primary Structure of Nucleic Acids Example 1

Here we're told that a pentanucleotide has a base sequence of g a u c a. Based on the given sequence, what is its likely origin? So where does this sequence originate from? And we can figure this out based on this sequence. So these are our nitrogenous bases. Because they're Nitrogenous bases, that will rule out Fructose which is a Carbohydrate, and Olic Acid because it's a fatty acid. Because these are nitrogenous bases, that means that's gonna be either DNA or RNA. Now, what's the key differences between them? Remember, the key difference is that DNA uses Thymine as one of its nitrogenous bases abbreviated T And RNA uses Uracil, abbreviated u. Since there is a Uracil involved within this sequence, it would have to be RNA that's being discussed here. So here, our final answer would be option c. This represents RNA as the origin for this nucleotide or base sequence.

Primary Structure of Nucleic Acids Concept 2

So now, remember that the primary structure of a nucleic acid is the sequence of nucleotides connected through phosphodiester bonds. With this idea, we have a new term, directionality. Now, this is the sequence of nucleotides being read and it's read from the 5 prime end to the 3 prime end. A good way to remember which end is which is our memory tool which is phosphate, phosph sounds like the letter f, equals 5. So here, we're going to say that this is, 2 nucleotides connected by a phosphodiester bond. If we imagine it just being elongated further by more nucleotides and more phosphodiester bonds, we'd say at this end where we have our free phosphate group, phosphate equals 5, this would be our 5 prime end. And if that's the 5 Prime end, then down here where we have this free o h group, that represents our 3 Prime end. And again, we're reading it from 5 Prime to 3 Prime, so looking at this arrow we're going from 5 Prime to 3 Prime. This is how we interpret the primary structure of nucleic acid if we're reading the chain of nitrogenous bases involved. Because here, the nitrogenous bases is where we can get differentiation in terms of our different primary structures of nucleic acids. Different orders of our nitrogenous bases in turn over time could lead to different types of proteins being created from this primary structure. Right? So just keep that in mind. Phosphate equals 5. The free phosphate end is the 5 prime end. The free o h end is the 3 prime end.

Primary Structure of Nucleic Acids Example 2

In this example question it says, which of the following statements about primary nucleic acid structure is incorrect? A. The structure and function of a nucleic acid is based on the sequence of the connected nucleotides. That there is true. The sequence of nitrogenous bases is read from the 5 prime to the 3 prime end. This is directionality, so this statement is also true. Phosphodiester bond represents a bond between the phosphate group and the sugar. That is also true. So here, the last one, the difference between Nucleic Acids is a result in the difference of the sugar attached to the backbone. So remember, the diversity or differences between our nucleic acids is really based on the differences in their nitrogenous bases, not the backbone. So this statement, d, is a statement that is incorrect out of all the options given.

Draw the full structure of the DNA trinucleotide G-A-T and label its 5’ and 3’ ends. 

• A.
• B.
• C.
• D.

Draw the following primary structure based on the following description: 

Draw 3 nucleotides with deoxyribose sugars with dTMP bases connected by phosphodiester bonds. 

• A.
• B.
• C.
• D.