This lesson addresses the types of nucleic acids and their structures. It contains illustrations and detailed descriptions about the various components that form these molecules. A summary and brief quiz are also included.
The Forms of Nucleic Acid
What makes people look physically different from one another? Why do some people have dark hair while others have light hair? What about height? Why can it vary so drastically from one person to the next? The answer to these questions resides in our DNA. DNA, or deoxyribonucleic acid, is the genetic material that codes for particular traits. All organisms contain either DNA or RNA, ribonucleic acid. Ribonucleic acid is another form of genetic material that is used within living organisms.
Both DNA and RNA are forms of nucleic acids. Nucleic acids are large molecules used by living organisms to code for specific characteristics.
The Structure of Nucleic Acid
Since we now know that DNA and RNA are the two types of nucleic acids, we can focus our attention on their respective structures. To begin, let’s look at DNA.
Below is a simple illustration to get us started:
DNA is often described as having a double helix structure. Essentially it resembles a twisted ladder. The sides of this ladder are made of a sugar and phosphate backbone.
The rungs are composed of four different compounds called nitrogenous bases. Nitrogenous bases are the specific compounds that spell out the genetic code for particular traits. They are often referred to using the letters A, T, C, and G rather than their chemical names.The bases of DNA are arranged in a specific manner. This is depicted in the graphic below. Notice how A (adenine), which is green, always lines up with T (thymine), which is purple.
In a similar manner C (cytosine), which is red, always pairs with G (guanine), which is blue. So, to recap, A bonds with T, and C bonds with G. This bonding pattern is known as base pairing. These bond patterns always exist within the nucleic acid DNA.
On the right of this image, you have the double helix design of DNA. Again there are four bases shown, along with their chemical structures. For the purposes of this lesson, we can ignore those structures.
Instead, focus your attention on the RNA molecule on the left. There are three primary differences between DNA and RNA.First, notice the similar nitrogenous bases making up an RNA molecule. C, G, and A (cytosine, guanine, and adenine) are all represented in RNA, just as they were in DNA. The noticeable difference between DNA and RNA is the nitrogenous base U (uracil). In RNA, U (uracil) replaces T (thymine).
Second, and most apparent, RNA is single stranded, unlike the double-stranded appearance of DNA. This is important because it means RNA can travel outside the nucleus, where genetic information is housed. That matters because the message contained in these molecules cannot be used to make your characteristics unless it leaves the nucleus.Finally, and less obvious, the backbone of RNA differs from that of DNA. In each molecule this structure is made from a sugar and phosphate. However, in DNA the sugar is called deoxyribose. In RNA the sugar is ribose.
These names represent different forms of a sugar molecule. While it isn’t vital that you understand the chemical nature of the structure, it is important to understand that DNA and RNA contain different types of sugar. Hence, the variation in names DNA vs.
Let’s review. There are two major types of nucleic acids found within living organisms. Nucleic acids are large molecules used by living organisms to code for specific characteristics. These nucleic acids are named DNA, deoxyribonucleic acid, which is the genetic material that codes for particular traits, and RNA, or ribonucleic acid, another form of genetic material that is used within living organisms. Each contains the genetic material that codes for particular traits.
The structure of DNA is described as a double helix. It contains a sugar phosphate backbone and the nitrogenous bases A, T, C, and G – adenine, thymine, cytosine, and guanine. Nitrogenous bases are the compounds that spell out your genetic code.
The backbone of DNA is like the sides of a ladder; the bases are like the rungs. The sugar in DNA is called deoxyribose. On the other hand, RNA is single-stranded. It also contains a sugar phosphate backbone. The sugar in RNA is called ribose and the nitrogenous bases are A, U, C, and G, the same as DNA’s bases but with uracil replacing thymine.