Nucleic Acids - Online Tutor, Practice Problems & Exam Prep

Nucleic acids, primarily DNA and RNA, are essential biomolecules that store and encode genetic information. They are composed of nucleotide monomers, which include a phosphate group, a pentose sugar, and a nitrogenous base. The nitrogenous bases are categorized into pyrimidines (cytosine, thymine, uracil) and purines (adenine, guanine). DNA forms a double helix structure with antiparallel strands, while RNA typically exists as a single strand. The formation of nucleic acids involves dehydration synthesis, creating phosphodiester bonds that establish a sugar-phosphate backbone with directionality.

Nucleic Acids

In this video, we're going to begin our lesson on nucleic acids. Nucleic acids, we know, are one of the major classes of biomolecule polymers, and it turns out that nucleic acids can have a variety of different types of functions. However, in our biology course, we're going to focus on the primary function of nucleic acids, which is really to store and encode genetic information or information that can be passed down from one generation to the next generation of life. An example of a nucleic acid is, of course, DNA. We'll get to talk more about DNA as we move forward in our course. But another example of a nucleic acid is also RNA as well. Once again, we'll get to talk more about DNA and RNA as we move forward in our class.

Now the monomers or the building blocks that are used to build nucleic acid polymers are referred to as nucleotides. You can see that there's a resemblance between nucleic acids and nucleotides just by looking at the first few letters here, the nucle, prefix here, and so that can be helpful to keep in mind. Nucleic acid polymers, similar to proteins, have directionality in their chain, meaning that one end of the chain will be chemically different than the other end of the chain. However, when it comes to nucleic acid polymers, the directionality is indicated with a 5' end and a 3' end. Moving forward in our course we'll get to talk more about the directionality and the difference between the 5' and 3' ends. But for now, we just need to know that there is directionality, and it's indicated with a 5' and three prime end.

Let's take a look at our example down below at the formation of nucleic acids from nucleotide monomers. Looking at this image, notice on the far left, we have these separate individual building blocks or monomers of nucleotides. We can label these as nucleotide monomers, and notice that they are separate and individual pieces here. But if we wanted to combine these separate pieces, these separate nucleotides and link them together into a chain like what we see over here on the right, then we're building ourselves a nucleic acid polymer. For example, a DNA polymer. Once again, it's also important to note that nucleic acid polymers, they have directionality, which means one end of the chain is going to be chemically different than the other end of the chain. We refer to this directionality, as we mentioned up above, as the 5' and the 3' ends. We can go ahead and put the 5' end over here and the 3' end over here. Once again, we'll get to talk more about the 5' and the 3' ends and exactly what they're referring to as we move forward in our course. But for now, this here concludes our introduction to nucleic acids, and we'll get to talk more about them as we move forward. So I'll see you all in our next video.

Nucleotides

In this video, we're going to talk a little bit more about nucleotides. And so we already know from our last lesson video that nucleotides are the monomers of nucleic acids. But really just one single nucleotide monomer consists of three different components that we have numbered down below here in our text. And also notice that we have the three components color-coordinated with these backgrounds, the first component has a pink background, the second component has a blue background, and the third component has a yellow background. These background colors correspond with the colors that you see down below in our image.

The very first component of a nucleotide monomer is a phosphate group, which, recall from our previous lesson videos, is just a functional group that looks like this down below, with a phosphorus atom in the middle. Now the second component of a nucleotide monomer is a pentose sugar, and all the pentose part means is that this sugar has a 5-membered ring. And so, when we take a look at the blue component down below, notice that there is a ring and the ring has a total of five members in it. And so that makes this a pentose sugar.

Then the third and final component of a nucleotide monomer is a nitrogenous base. And so it turns out that the nitrogenous base can vary, and there are five different types of nitrogenous bases. We'll talk more about those five different types of nitrogenous bases in our next lesson video. But for now, taking a look down below, we can see the third component is here in yellow, the nitrogenous base.

So, in our last lesson video, we were abbreviating nucleotides using symbols that look somewhat like this in the corner. But really just one of these nucleotide monomers that we see here in the corner consists of three components. Once again, the phosphate group here, the sugar component here, and the nitrogenous base up here. And you can think that this little nucleotide consists of these three components like what you see here.

Now this leads us to different types of nucleotides. There are DNA nucleotides or deoxyribonucleic acid nucleotides. So, DNA is the abbreviation for the molecule called deoxyribonucleic acid. And then there are also ribonucleic acid nucleotides or RNA nucleotides. And so the DNA and the RNA nucleotides, they use different sugars, amongst also, sometimes using different nitrogenous bases, which we'll talk more about as we move forward in our course.

But if we take a look at our image down below, notice that we're comparing DNA nucleotides versus RNA nucleotides. So the left half of our image over here is specifically for the DNA nucleotide, and the right half of our image over here is specifically for the RNA nucleotides. Notice that both nucleotides have the three components that we talked about before, the pink component here, which is the phosphate group. This one also has a phosphate group, the RNA nucleotide. They both also have a pentose sugar, and so you can see that the blue part is here. And then they both also have nitrogenous bases.

Now here specifically, we've said that the nucleotides of DNA and RNA use different sugars. So we're going to focus in on the blue part here and over here. And notice that the RNA over here on the right, it uses a ribose sugar, whereas the DNA over here on the left uses a deoxyribose sugar. And so the "deoxy" part here means "one less oxygen." "Oxy" means oxygen, and "d" means without. So, the deoxyribose sugar has one less oxygen in comparison to the ribose sugar over here. And so what this means is that the ribose sugar is going to have a hydroxyl group, an OH group at this position, and the deoxyribose over here is not going to have the extra oxygen. It's just going to have a hydrogen here. And so the deoxyribose has one less oxygen comparing this position to this position over here.

And so, we'll get to talk more about DNA and RNA as we move forward in our course, but, again, one of the biggest differences is that they use different sugars. DNA uses deoxyribose sugar, and RNA uses ribose sugar. So, this here concludes our introduction to nucleotides, and we'll be able to get some practice applying these concepts as we move forward in our course. So I'll see you in our next video.

Nucleic Acids Example 1

Alright. So here we have an example problem that's asking what is the difference between the sugar group in DNA and the sugar group in RNA. And we've got these 5 potential answer options down below. Now after reading through each of these 5 potential answer options, there's one that we can eliminate right off the bat, and that is going to be option e which says the sugar group in DNA and RNA are not different. Of course, we know that this is false, that DNA and RNA, they have different sugar groups from our last lesson video. Now option a here says the sugar group in DNA has a hexose while the sugar group in RNA is a pentose. Now a hexose, we did not mention at all in our last lesson video. We only talked about pentoses and recall pentoses are sugars with a 5 membered ring, whereas hexoses are sugars with a 6 membered ring. But we didn't mention anything about hexoses in our last lesson video and this is simply not true. Option a is not true, and both DNA and RNA use a pentose sugar.

Now option b says the sugar group in DNA has an extra hydroxyl group than the sugar group in RNA. Now recall hydroxyl groups are OH groups, so they have an oxygen in them, and recall that DNA stands for deoxyribose, and deoxy means one less oxygen. And so if DNA had an extra hydroxyl group that would mean it would have an extra oxygen, but that is not the case with DNA. It is deoxy. So that means it has one less, not one extra hydroxyl group. And so for that reason, we can go ahead and eliminate answer option b. And then of course, looking at answer option c here, it says the sugar group in DNA has one less hydroxyl group than the sugar group in RNA. And then, of course, this is going to match up with what we were just talking about, and this is going to be the correct answer here for this example problem. Now option d here says the sugar group in DNA contains one less carbonyl group than the sugar group in RNA, but, the carbonyl group is not the right functional group here. Remember, carbonyl groups are C=O groups. But we're looking at the hydroxyl group, not the carbonyl group. So that's why option d is incorrect. And so, once again, option c here is the correct answer for this example problem.

And if we were to take a look at our last lesson video here, we can see that the DNA nucleotide over here has one less oxygen in comparison to the ribose, which has an extra oxygen atom. And so, the deoxy therefore has one less hydroxyl group, relative to the ribose which has one additional hydroxyl group. And so that concludes this video and I'll see you all in our next one.

Which of the following descriptions best fits the class of molecules known as nucleotides?

a) A nitrogenous base & a phosphate group.

b) A nitrogenous base & a sugar.

c) A nitrogenous base, phosphate group & a sugar.

d) A nitrogenous base, a carbohydrate, & a sugar.

• A. A nitrogenous base & a phosphate group.
• B. A nitrogenous base & a sugar.
• C. A nitrogenous base, phosphate group & a sugar.
• D. A nitrogenous base, a carbohydrate, & a sugar.

5 Nitrogenous Bases

So now that we know that one of the components of a single nucleotide monomer is the Nitrogenous Base, in this video we're going to focus on the 5 Nitrogenous Bases. And so once again there are 5 different Nitrogenous Bases and these 5 nitrogenous bases can be grouped together as either pyrimidines or as purines. The pyrimidines are single-ringed molecules, whereas the purines are double-ringed molecules. If we take a look at our image down below, on the left-hand side, notice that we're showing you the nitrogenous bases, which can once again be grouped into these two groups: the pyrimidines, which we have over here on the left-hand side, and the purines, which we have over here on the right-hand side. Also note the pyrimidines, as we mentioned above, are all single-ringed molecules, so they only have one single ring, whereas the purines over here are all double-ringed molecules, so they all have 2 rings like what we see here. These are called nitrogenous bases for a reason, because they have plenty of nitrogen atoms, as you can see, what I'm highlighting right here. All of these nitrogen atoms make these bases pretty nitrogenous, and that's why we call them nitrogenous bases.

It's also important to note that each of these nitrogenous bases has a name, so you can see we have cytosine, thymine, and uracil are the pyrimidines, and then we have adenine and guanine as the purines. Notice that each of these nitrogenous bases' names has a unique first letter. For instance, cytosine's first letter is unique. It's the only one that starts with a "c" and so we can use the first letter "c" to abbreviate cytosine. Thymine's unique first letter is "t", uracil's unique first letter is "u", adenine's unique first letter is "a", and guanine's unique first letter is "g". We can abbreviate these nitrogenous bases just by using the one letter. Notice that when we introduced pyrimidines up above that we made the "y" here in pyrimidines interactive for you to fill out yourselves as you watch this video. Notice that most of the pyrimidines, which have a "y" in them, also have a "y" in them themselves. So, cytosine and thymine have "ys" in them, which make them pyrimidines. Notice that the purines, such as adenine and guanine, do not have a "y" in them and so, they're gonna be batched over here. The only exception to this "y" is uracil. Uracil is a pyrimidine even though it doesn't have a "y". But if you can just remember this one exception, then that'll help you batch these nitrogenous bases into the correct groups.

Down below the image, we have memory tools to also help you group and batch these nitrogenous bases. So when you think of pyrimidines, that kinda sounds like pyramids. When you think about pyramids, you think about the Egyptian pyramids. And of course, we all know that underneath the Egyptian pyramids there are creepy tombs. So, the "c" in creepy is for the "c" in cytosine, the "t" in tombs is for the "t" in thymine, and, of course, the "u" in under is for the "u" in uracil. By remembering pyrimidines, thinking about pyramids, you'll think about the creepy tombs under the pyramids and you'll be able to group these nitrogenous bases no problem. On the other hand, the purines, all you gotta do is think about pure as gold. So here we got this guy. He's got some gold in his hand, and he's thinking pure as gold. So, the "a" in "as" is for the "a" in adenine, and, of course, the "g" in gold here is for the "g" in guanine. By remembering that purines are pure as gold, you'll be able to determine these, adenine and guanine are purines no problem.

Another important thing to note here is that thymine is a nitrogenous base that is uniquely only found in DNA, whereas uracil on the other hand is a nitrogenous base that is uniquely found only in RNA. In RNA structure, what we'll see is that all of the "t's" are going to be replaced with "u's". So, "u's", once again, are specific for only in RNA, whereas "t's" are specific for only in DNA. This is an easy way for us to be able to identify if a strand is DNA or RNA just by looking to see if "t's" or "u's" are being used. This leads us to talk a little about DNA structure here because in DNA structure, the nitrogenous bases on different DNA strands are going to base pair together. The base pairing works in this fashion where adenines or "a's" are always going to pair with thymines or "t's", and cytosines or "c's" are always going to pair with guanines or "g's". You can see that a purine is always going to be paired up with a pyrimidine. So "a's" pair with "t's". And then, once again, the pyrimidine of cytosine is always going to be paired up with a purine of guanine. So, they always pair up a pyrimidine with a purine. If we look at the image on the right-hand side, notice that it's focusing on DNA base pairing. DNA is made up of 2 strands. What you'll see is that there's one strand over here on the left and there's another strand over here on the right. These two strands connect to each other via interactions between the base pairs, where once again "a" always pairs with "t" and "c" always pair with "g". Notice that the "a" over here on this strand is always gonna pair with "t's" on this strand and vice versa, and the "c's" on this strand are always gonna pair with the "g's" on this strand over here and vice versa. Adenines will always pair with thymines, and cytosines will always pair with guanines, which is really important to note here.

This concludes our introduction to the 5 nitrogenous bases and we'll be able to get some practice applying these concepts as we move forward. So I'll see you all in our next video.

Nucleic Acids Example 2

Alright. So here we have an example problem that wants us to complete the blank here using one of these 6 potential answer options down below. And the example problem says the purine nitrogenous bases are blank. And so of course, if we recall from our last lesson video that one of the ways we can use to help us remember the purine nitrogenous bases is to remember purines are pure as gold. And so by remembering pure as gold, we can see that the "a" in the "as" is for Adenine and the "g" in the gold is for Guanine. And so Adenine and Guanine are the purines. And so of course when we look at the answer options we can see that option E says adenine and guanine. And so that is going to be the correct answer for this example problem and all of the other ones are incorrect. And so, that concludes this example problem and I'll see you all in our next video.

The four nitrogenous bases commonly found if DNA are: 

a) Adenine, thymine, cytosine, uracil 

b) Uracil, adenine, cytosine, guanine.

c) Uracil, cytosine, guanine, thymine.

d) Adenine, thymine, cytosine, guanine.

e) None are correct.

• A. Adenine, thymine, cytosine, uracil
• B. Uracil, adenine, cytosine, guanine.
• C. Uracil, cytosine, guanine, thymine.
• D. Adenine, thymine, cytosine, guanine.
• E. None are correct.

Formation & Breakdown of Nucleic Acids

In this video, we're going to talk about the formation and the breakdown of nucleic acids. Recall from our previous lesson videos that if we want to build a polymer, then we're going to need a dehydration synthesis reaction. Dehydration synthesis reactions are going to link individual and separate nucleotides together so that they can begin to build the nucleic acid polymer. Now, the covalent bonds that link these nucleotides together are specifically referred to as phosphodiester bonds. Notice that we have this yellow background behind the phosphodiester bonds in the text and that's because it links to the yellow color that we have down below in our image, which we'll be able to see shortly.

The formation of phosphodiester bonds between nucleotides results in the sugar phosphate backbone of the nucleic acid, and the nucleic acid backbone has directionality, as we already indicated in our previous lesson video. We know that there's going to be a _5' prime end and a _3' prime end. Here, we're specifically indicating that the _5' prime end is going to be the phosphate group end, which we'll be able to see down below. And the _3' prime end is going to be the free hydroxyl group, the hydroxyl end. Let's take a look at our image down below to start to clear some of this up.

We're looking at phosphodiester bond formation, and notice on the far left-hand side we're showing you ₂ separate nucleotide monomers. Here we're showing you a cytosine and here we're showing you a thymine. What you'll also notice is that these are specifically deoxyribonucleotides or DNA nucleotides because this position here is not containing a hydroxyl group—it has one less oxygen, deoxy. These are DNA nucleotides. Notice that they're separate over here.

If we want to join them together so that we can start to build a DNA polymer, then we're going to need the dehydration synthesis reaction, which we know is used to build up polymers. The dehydration synthesis dehydrates the molecule, releasing a water molecule, and synthesizes a larger molecule in the process. Notice that, over here, these two nucleotides are joined together via this bond that we have highlighted in yellow, and this is specifically referring to the phosphodiester bond.

You'll note that there is a sugar phosphate backbone formed here where we have alternating sugar and then phosphate, and then sugar and then phosphate, and this is what we call the sugar phosphate backbone, we have the nitrogenous bases. Once again, this sugar phosphate backbone has directionality. It has a _5' prime end and a _3' prime end. The _5' prime end is going to be the phosphate group end, the end that has the free phosphate group. So when we take a look at our image down below, notice that the free phosphate group is over here on this end. And this will be the _5' prime end for that reason. And then, of course, the _3' prime end is going to be the end that has the free hydroxyl group. Taking a look down below here, notice that there's a hydroxyl group at this end, the opposite end, and so this is going to be the _3' prime hydroxyl end.

This here really concludes our introduction to the formation and the breakdown of nucleic acid polymers, and we'll be able to get some practice applying the concepts that we've learned here as we move forward in our course. I'll see you all in our next video.

DNA vs. RNA

In this video, we're going to briefly compare and contrast DNA and RNA. Recall that DNA is an abbreviation for deoxyribonucleic acid. DNA's primary function is to store genetic or hereditary information inside of the cell. This is information that would be passed down from one generation to the next. We'll talk more about the functions of DNA later in our course. In this video, we're mainly going to focus on the structure of DNA. DNA forms a structure that scientists refer to as a double helix. They call it a double helix because DNA is made up of two strands, and those two strands form a helix, a twisting, winding ladder type of structure that we'll be able to see down below in our image. The two strands that make up the DNA molecule are actually antiparallel with respect to each other. "Antiparallel" means that their directionality is going in opposite directions. These two strands go in opposite directions in terms of their directionality. We'll also be able to see the antiparallel strands down below in our image. They're connected to each other via hydrogen bonds that form between the nitrogenous base pairs. So, on the left-hand side of our image over here, notice that we're showing you DNA, deoxyribonucleic acid. DNA forms a double helix structure, meaning it has two strands. You can see one strand here and the other strand here. These two strands wind onto each other, forming hydrogen bonds between the base pairs. If we were to unwind the DNA so that it has this type of structure down below, you'll see the DNA base pairs where Cs always pair with Gs and As always pair with Ts. You can see the color coordination here and see how they always pair in that fashion. This represents one DNA strand, and this down here represents the other DNA strand. You can see that this blue structure represents the sugar phosphate backbone, and we know from our last lesson video that sugar phosphate backbones of nucleic acids have directionality. Notice that this end of the sugar phosphate backbone for the strand is the 5' end, which means that the opposite end over here is going to be the 3' end. It's going from 5' to 3' left, from left to right in that direction. However, notice that the opposite strand over here, its 5' end is over here on the right, so that means its 3' end must be over here on the left. The bottom strand is going from 5' to 3' from right to left in the opposite direction as the top strand. Because we have two strands that are going in opposite directions, that makes these two strands in the DNA molecule antiparallel with respect to each other. If they were going in the same direction that would make them parallel, but because they're going in opposite directions that makes them antiparallel.

Now, on the other hand, RNA is the abbreviation for ribonucleic acid. RNA has a variety of different functions. We'll talk more about the functions of RNA later in our course. One of the primary functions of RNA is to act as a template for synthesizing or building proteins. In terms of the structure of RNA, RNA usually forms a single-stranded nucleotide chain rather than forming a double helix like DNA. So, if we take a look at our image over here on the right-hand side, notice that we're showing you RNA, which is usually a single-stranded structure. You can see the single strand of RNA right here. The single-stranded RNA will have a sugar phosphate backbone that has directionality. If this is the 3' end over here, that means the opposite end must be the 5' end. RNA specifically uses nitrogenous bases of Us instead of using the nitrogenous bases of Ts like DNA. So, T is specific for DNA, whereas Us are specific for RNA. RNA is normally a single-stranded structure, but base pairing can still apply if it binds to itself. Sometimes RNA can fold up onto itself and bind to itself, forming complex structures. Also, RNA can sometimes bind to small anticodons, which again we'll talk a lot more about later in our course. You can see that this is how the RNA would base pair in the same way as DNA, except replacing the T with the U, and that's really the main takeaway. This concludes our introduction to the differences between DNA and RNA, and we'll get some practice applying these concepts as we move forward in our course. I'll see you all in our next video.

Which of the following statements about DNA structure is true?

a) The nucleic acid strands in a DNA molecule are oriented antiparallel to each other.

b) Nucleic acids are formed through phosphodiester bonds that link complementary nucleobases together.

c) Hydrogen bonds formed between the sugar-phosphate backbones of the two DNA chains stabilize the structure.

d) The pentose sugar in DNA is ribose (containing two hydroxyl groups).

• A. The nucleic acid strands in a DNA molecule are oriented antiparallel to each other.
• B. Nucleic acids are formed through phosphodiester bonds that link complementary nucleobases together.
• C. Hydrogen bonds formed between the sugar-phosphate backbones of the two DNA chains stabilize the structure.
• D. The pentose sugar in DNA is ribose (containing two hydroxyl groups).