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. Phosphodiester bonds link nucleotides, creating a sugar-phosphate backbone with directionality, marked by 5' and 3' ends.

Nucleic Acids

In this video, we're going to begin our lesson on nucleic acids. And so, 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. And so, an example of a nucleic acid is, of course, DNA. And so, 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. And 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. And so, you can see that there is 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. Now, 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. And 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 3′ end. So let's take a look at our example down below at the formation of nucleic acids from nucleotide monomers. And so, looking at this image, notice on the far left, we have these separate individual building blocks or monomers of nucleotides.

So we can label these as nucleotide monomers, And so 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. Now, 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. And so, we refer to this directionality, as we mentioned up above, as the 5′ and the 3′ ends. And so we can go ahead and put the 5′ end over here and the 3′ end over here.

And 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 3 different components that we have numbered down below here in our text. And also notice that we have the 3 components color coordinated with these backgrounds, where the first component has a pink background, the second component has a blue background, and the third component has a yellow background. And these background colors correspond with the colors that you see down below in our image.

And so 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 5 members in it. And so that makes this a pentose sugar. And 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 5 different types of nitrogenous bases. And we'll talk more about those 5 different types of nitrogenous bases in our next lesson video. But for now, taking a look down below, we can see the 3rd 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 3 components, once again, the phosphate group here, the sugar component here, and the nitrogenous base up here.

And so 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 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. 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. So notice that both nucleotides have 3 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 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.

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. Recall that 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. 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. 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 double bond 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.

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. And so the pyrimidines are single ringed molecules, whereas the purines are double ringed molecules. And so if we take a look at our image down below over here 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. And notice that the pyrimidines, as we mentioned up 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.

Now also these are called nitrogenous bases for a reason, because they have plenty of nitrogen atoms as you can see, which I'm highlighting right here. All of these nitrogen atoms make these bases pretty nitrogenous, and that's why we call them nitrogenous bases. Now it's also important to note that each of these nitrogenous bases has a name. And so you can see we have cytosine, thymine, and uracil are the pyrimidines, and then we have adenine and guanine as the purines. And so notice that each of these nitrogenous bases names has a unique first letter.

And so for instance, cytosine's first letter is 'c', 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'. And so we can abbreviate these nitrogenous bases just by using the one letter. Now notice that when we introduced pyrimidines up above that we made the 'y' here in pyrimidines interactive for you guys to fill out yourselves as you watch this video.

And the reason that we're emphasizing this 'Y' here is because notice that most of the pyrimidines, which have a 'y' in it, also have 'y's in them themselves. So, cytosine and thymine have 'y's in them, which make them pyrimidines. And, notice that the purines, such as adenine and guanine, they do not have a 'Y' in them, and so, they're going to be batched over here. And really the only exception to this 'Y' is going to be the 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. Now, what you'll also notice is down below the image, we have this memory tools to also help you group and batch these nitrogenous bases. So when you think of pyrimidines, that kind of sounds like pyramids, and 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 under those pyramids. And so here we have an image of the creepy tombs under the Egyptian pyramids.

And so you can think that, the 'c' in creepy is for the 'c' inside of cytosine, the 't' in tombs is for the 't' in thymine, and, of course, the 'u' and under is for the 'u' in uracil. And so, 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 got to 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. And so what you can see here is that the 'a' in as is for the 'a' in adenine, and, of course, the 'g' in gold here is for the 'g' in guanine.

And so by remembering that purines are pure as gold, you'll be able to determine these, adenine and guanine are purines no problem. Now 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. And so in RNA structure, what we'll see is that all of the 't's are going to be replaced with 'u's. And so, 'u's, once again, are specific for only in RNA, whereas 't's are specific for only in DNA. So that's 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.

Now this leads us to talk a little bit about DNA structure here because in DNA structure, the nitrogenous bases on different DNA strands are going to base pair together. And so 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. And so what you can see is 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 pyrimidine with a purine. Now, if we take a look at the image over here on the right-hand side, notice that it's focusing in on DNA base pairing. And so DNA is made up of 2 strands. And so 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. And these two strands, they connect to each other via interactions between the base pairs, where once again 'A' always pairs with 'T' and 'C' always pair with 'G'.

So notice that the 'A' over here on this strand is always going to pair with 'T's on this strand and vice versa, And the 'C's on this strand are always going to pair with the 'G's on this strand over here and vice versa. And so, once again, adenines will always pair with thymines, and cytosines will always pair with guanines. And so this is really important to note here. And so this here really 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.

Formation & Breakdown of Nucleic Acids

In this video, we're going to talk about the formation and the breakdown of nucleic acids. And so 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. And 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 here shortly.

Now the formation of phosphodiester bonds between nucleotides is going to result in the sugar-phosphate backbone of the nucleic acid. And the nucleic acid backbone is going to have directionality as we already indicated in our previous lesson video. So we know that there's going to be a 5 prime end and a 3 prime end. We're specifically indicating that the 5 prime end is going to be the phosphate group end, the free phosphate group, 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. 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. And 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, and notice that they're separate over here. If we want to join them together to start to build a DNA polymer, 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 it synthesizes a larger molecule in the process. Notice that these two nucleotides are joined together via this bond that we have highlighted in yellow, a phosphodiester bond.

What you'll note is that there is a sugar phosphate backbone that has been formed here where we have alternating sugar and then phosphate, then sugar and then phosphate, and so this is what we call the sugar-phosphate backbone. And branching off of 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.

When we take a look at our image down below, notice that the free phosphate group is over here on this end, and so 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. 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.

We'll be able to get some practice applying the concepts that we've learned here as we move forward in our course. So 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 the cell. This is information that is 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. It's called a double helix because DNA is composed of two strands, and those two strands form a helix, a twisting winding ladder-type structure that we'll discuss in detail. These two strands that make up the DNA molecule are anti parallel with respect to each other. "Anti parallel" means that the directionality of the strands goes in opposite directions.

Returning to their orientation, these two strands are 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. Once again, DNA forms a double helix structure. It consists of two strands - one strand is shown here and another there. They wind onto each other, forming hydrogen bonds between the base pairs. If we were to unwind the DNA, you would see the base pairs where c's always pair with g's, and a's always pair with t's. You can see the color coordination here.

This here represents one DNA strand, and this down here represents the other DNA strand. You can see that the blue structure represents the sugar phosphate backbone. As we know from our last lesson video, the 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 the 3' end, going from 5' to 3' left to right. However, the opposite strand over here, its 5' end is on the right, which means that its 3' end is on the left.They are going in opposite directions, making these strands anti parallel to each other. If they were going in the same direction, that would make them parallel, but because they're going in opposite directions, they are anti parallel.

On the other hand, RNA is the abbreviation for ribonucleic acid. RNA has a variety of functions which we will discuss more in our course. A primary function of RNA is to act as a template for synthesizing proteins. Regarding the structure of RNA, it usually forms a single-stranded nucleotide chain rather than a double helix like DNA. On the right-hand side of our image, you can see the single strand of RNA. The single-stranded RNA also has a sugar phosphate backbone with directionality.

If this is the 3' end over here, that means the opposite end must be the 5' end. RNA uses nitrogenous bases of U instead of the T bases used in DNA, and U is 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 upon itself and bind, forming complex structures. RNA can also sometimes bind to small anticodons, a topic we will delve into later in our course. You can see how RNA would base pair in the same way as DNA, replacing the T with U, which is the main takeaway. This concludes our introduction to the differences between DNA and RNA, and we'll be able to 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).

Here’s what students ask on this topic:

What are the primary functions of nucleic acids?

Nucleic acids, primarily DNA and RNA, serve essential roles in storing and transmitting genetic information. DNA (deoxyribonucleic acid) stores hereditary information that is passed from one generation to the next, ensuring the continuity of genetic traits. It forms a double helix structure, which allows it to be stable and efficiently store vast amounts of genetic data. RNA (ribonucleic acid), on the other hand, plays a crucial role in protein synthesis. It acts as a template for translating genetic information from DNA into proteins, which are vital for various cellular functions. RNA is typically single-stranded and can fold into complex structures to perform its functions. Together, DNA and RNA ensure the proper functioning and reproduction of living organisms.

What are the differences between DNA and RNA?

DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) differ in several key aspects. Structurally, DNA is a double-stranded molecule forming a double helix, while RNA is usually single-stranded. The sugar in DNA is deoxyribose, which lacks one oxygen atom compared to the ribose sugar in RNA. DNA contains the nitrogenous bases adenine (A), thymine (T), cytosine (C), and guanine (G), whereas RNA contains adenine (A), uracil (U), cytosine (C), and guanine (G). Functionally, DNA stores genetic information, while RNA translates this information into proteins. Additionally, DNA is more stable and remains in the nucleus, whereas RNA is more versatile and can travel to different parts of the cell.

What are the components of a nucleotide?

A nucleotide, the building block of nucleic acids, consists of three components: a phosphate group, a pentose sugar, and a nitrogenous base. The phosphate group is a functional group containing phosphorus and oxygen atoms. The pentose sugar can be either ribose (in RNA) or deoxyribose (in DNA), with ribose having one more oxygen atom than deoxyribose. The nitrogenous base can be one of five types: adenine (A), guanine (G), cytosine (C), thymine (T), or uracil (U). In DNA, the bases are A, G, C, and T, while in RNA, the bases are A, G, C, and U. These components link together to form the nucleotide structure, which then polymerizes to form nucleic acids.

How do nucleotides form nucleic acid polymers?

Nucleotides form nucleic acid polymers through a process called dehydration synthesis, which involves the removal of a water molecule to form a covalent bond. Specifically, nucleotides are linked by phosphodiester bonds, which connect the phosphate group of one nucleotide to the hydroxyl group of the pentose sugar of another nucleotide. This linkage creates a sugar-phosphate backbone with directionality, marked by 5' (five prime) and 3' (three prime) ends. The 5' end has a free phosphate group, while the 3' end has a free hydroxyl group. This directional chain of nucleotides forms the structure of DNA and RNA, allowing them to store and transmit genetic information effectively.

What are the five nitrogenous bases and how are they categorized?

The five nitrogenous bases found in nucleic acids are adenine (A), guanine (G), cytosine (C), thymine (T), and uracil (U). These bases are categorized into two groups: purines and pyrimidines. Purines, which have a double-ring structure, include adenine and guanine. Pyrimidines, which have a single-ring structure, include cytosine, thymine, and uracil. In DNA, the bases are adenine, guanine, cytosine, and thymine, while in RNA, the bases are adenine, guanine, cytosine, and uracil. The specific pairing of these bases (A with T or U, and C with G) is crucial for the structure and function of nucleic acids.