Nucleic acids - DNA and RNA structure

Nucleic acids - DNA and RNA structure

In this article we will study about nucleic acids. Nucleic acids are basically biopolymers, which are made of monomeric units known as nuclotides. We have two important functions for nucleic acids, that is, they hold our genetic information and they perform a variety of other functions that we will discuss later. There is 2 types of nucleic acids [NA] in the body, the DNA & RNA.

 Let's first try to understand the definition of nucleic acids. So, nucleic acids are biopolymers.

They are polymers, which means they are made of repeated units called monomers, which in this case are nucleotides. Now take this example. We have many different types of biopolymers in our body; one of them are the proteins.

 And most of you know that the proteins are made up of repeated units called amino acids, same Nucleic acid is also made of repeated unit of nucleotide polymer.

 Which are made up of repeated units which are known as nucleotides. The next important thing is to understand the basic structure of a nucleotide, which will help us understand the structure of nucleic acids in detail.

Nucleic acid diagram.

As you can see, the single nucleotide is made up of three important groups: The phosphate, sugar, nitrogenous base, and these groups are attached to one another by bonds, which we will discuss later.

To understand the complete structure of a nucleotide, let's try to understand the structure of these groups one by one.

Sugar Molecule Structure:

the 6C sixth carbon sugar molecule present inside body cells, and for example is the glucose. In chemical nomenclature, all six carbon sugars are called hexoses, the word "hex" meaning "six." There are different types of hexoses in our body other than glucose like the mannose and galactose Similarly, five carbon sugars are called pentoses, the word "pent" meaning "five." There are different types of pentoses in our body, but the two important types of pentoses that are present in the nucleic acids are the ribose, and the deoxyribose.

you can see the structure clearly. Comparative studies of Ribose vs Deoxyribose, We have carbon atoms on each of these corners. Note that the last carbon atom is located outside the ring.  oxygen molecule at center carbon position. You can also see in this chemical structure that the carbon atoms are named from one to five in a clockwise direction.

So the carbon atom next to the right of the oxygen is called C1, so C2, C3, C4 and C5 C5 is located outside the ring. You can also see in this chemical structure we have different types of functional groups attached to these carbon atoms like the hydroxyl group and the hydrogen atom. The most important of these functional groups, which determine whether the sugar is ribose or deoxyribose are present at the carbon number 2 and the carbon number 3. In the sugar ribose, we have a hydroxyl group that is attached to the carbon number 2. This is the chemical structure of ribose Now,

if you compare this structure with the structure of deoxyribose, the only major difference is at carbon number 2 the carbon number 2 contains only a hydrogen atom.

Here, you can see the carbon number 2 in deoxyribose contains only a hydrogen atom, whereas in ribose the carbon number 2 contains a hydroxyl group.

 DNA is stable as compared to RNA only because of 2’dideoxyribose sugar.

phosphate group:

 The next important group we're studying for the structure of nucleotides is the phosphate group which is this little detail here. The phosphare group consists of a phosphorus atom in the center, to which four oxygen atoms are attached, which are negatively charged. phosphate group is similar to phosphate group that present in [ATP] adenosine triphosphate.

that energy-carrying molecule in the body. However, in ATP we have three molecules of phosphate, which are attached to one another by high-energy phospho-ester bonds. The phosphate group is a polar molecule due to the presence of highly ionized oxygen atoms, which impart negative charge to the phosphate group.

 Nitrogenous bases are basically molecules that contain nitrogen in varying amounts, and they act as a base. Most of you know that the human body contains organic chemicals, which have carbon, hydrogen and oxygen in varying amounts. In nitrogenous bases, nitrogen combines with all of these atoms to form ring-like structures. These molecules are called bases since they can donate electrons to other molecules and form new molecules in this process. The nitrogen combines with all of these other atoms to form ring structures.

 Now, we can have two different types of ring structures. single rings structure & double rings structure. The single rings are called pyramidines. And the double rings are called purines. We have three different types of pyramidines: the thymine, cytosine, and the uricil. And we have two different types of purines, called adenine, and guanine. In the center you can see the chemical structure of each of these bases. As you can see, the purines, which are the double-ring structures, adenine and guanine.

The thymine, cytosine and uracil all are single-ring structures, and they are smaller as compared to the purines. The difference in the size of these bases is very important, as it helps to bear these bases in the structure of DNA properly, which we'll study later. So now you know the individual structures which are present in a single nucleotide. Next we will look at how these individual structures bond to each other to form a single nucleotide, and then we will look at how many nucleotides bind to each other to form a chain of nucleotides, which is called a polynucleotide, which can be either DNA or RNA.

the bond formed will be between the N1 of the pyramidine ring and the C1 of the sugar.

 If you want to go into the details about how these nitrogens are named, you can check the link in the description below for IUPAC nomenclature for the aromatic compounds. Now this bond will be an example of a glycosidic bond, which is a covalent bond which links carbohydrates with other structures. If we have to pair a purine ring at a similar position, the bond formed will be between the N9 of the purine ring. Next, let's attach the phosphate. 

The phosphate group attaches with the carbon number 5 of the sugar, and the bond formed is the example of the ester bond which is also a strong covalent bond. So now you know how the three structures in a single nucleotide bind to each other to form one nucleotide. Next, we look at how many nucleotides bind to each other to form a chain of nucleotides called a polynucleotide. You can see basically what happens is that the phosphate group that attaches to the carbon number 5 of the sugar below also forms a bond with the carbon number 3 of the sugar above, and this pattern is repeated again and again. So you can see that the phosphate groups form bonds both above and below the chain of these nucleotides. As a result, a long chain of nucleotides is formed which consists of a sugar-phosphate backbone and in the center we have all these nitrogenous bases, which project from the sugar-phosphate backbone.

 Now here comes the rule of complementary base pairing. What complimentary base pairing says is that only adenine forms a hydrogen bond with thymine, and only guanine forms a hydrogen bond with cytosine. 

This is a universal rule that is applied in the structure of DNA. Here you can see adenine forms a hydrogen bond with thymine, and similarly thymine forms a hydrogen bond with only adenine. In similar case, guanine forms a hydrogen bond with cytosine and vice versa.

 You can see that the supports of the ladder in red are basically representing the sugar-phosphate backbone and the rungs of the ladder represent the nitrogenous bases that are forming hydrogen bonds with each other. Of course, the original structure of DNA is that of a double helix, so you you can compare the structure with a double helix, where the helices of the structure represent the sugar-phosphate backbone, and in the center you can see the red lines which represent the different nitrogenous bases that are forming bonds with each other.

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