Structure Of Nucleic Acids - Structure Of DNA - Structure Of RNA - DNA Structure And RNA Structure

In this video we cover the structure of nucleic acids, DNA and RNA. We discuss the components of each, and the differences between the two.
Transcript with notes.

There are 2 main types of nucleic acids, DNA or deoxyribonucleic acids and RNA or ribonucleic acids. Nucleic acids are large molecules made up of smaller molecules called nucleotides. DNA contains deoxynucleotides and RNA contains ribonucleotides. The nucleotides in these molecules are linked together through covalent bonds or bonds where electrons are shared between atoms.

Let’s start by looking at DNA. The nucleotides that make up DNA have 3 parts, a phosphate group, a nitrogenous base, and a deoxyribose sugar, or 5 carbon sugar. The phosphate group consists of a phosphate bonded to 4 oxygen atoms, with one of the oxygen’s bonded to the number 5 carbon of the deoxyribose sugar. An important note here, the number 2 carbon of the deoxyribose’s sugar is bonded to a hydrogen atom. Carbon atom number one of the deoxyribose sugar is bonded to the nitrogenous base.

There are 4 types of nitrogenous bases that can be found in DNA, adenine, shown bonded here, guanine shown here, cytosine shown here, and thymine shown here. As you can see, adenine and guanine have double ring structures, and cytosine and thymine have sing ring structures. Adenine and guanine are called purine bases and cytosine and thymine are called pyrimidine bases.

DNA is a double stranded nucleic acid and its molecules take on a helical formation. Each helical chain has its phosphate-sugar group toward the outside, and the nitrogenous bases facing inwards towards the nitrogenous bases of the other chain. Each of the bases on one chain is joined to the base in the other chain through either 2 or 3 hydrogen bonds.

Thymine and adenine are joined by 2 hydrogen bonds and cytosine and guanine are joined by 3 hydrogen bonds. Thymine and adenine are always a base pair, and cytosine and guanine are always a base pair. It is estimated that a DNA molecule contains more than 100 million of these base pairings, and in one individuals body, the sequence of these base pairings is the same in every DNA molecule. So this sequence of base pairing is unique to that individual.

DNA is often called the information molecule because it contains the master code needed to make various RNA molecules and protein molecules in the body.

Now for RNA. The nucleotides that make up RNA are very similar to those that make up DNA. RNA nucleotides have a phosphate group with the same structure as in DNA. They have a 5 carbon sugar, but the number 2 carbon is bonded to a hydroxyl OH group instead of a lone hydrogen atom, and this sugar is called ribose.

It also consists of 3 of the same nitrogenous bases as DNA, cytosine, adenine, and guanine. But it does not contain thymine, instead it contains uracil, which is also a single ring structure like thymine, making it a pyrimidine base.

Most RNA molecules are single stranded nucleic acids and many times they form a folded compacted structure with some hydrogen bonding taking place within base pairs of the molecule. These pairings are the same as in DNA, cytosine and guanine are a base pair, and uracil takes the place of thymine and pairs with adenine.

RNA is important in the process of forming different proteins in the body, of which we will cover in depth in a later video.

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