Nucleic Acids

Hey, guys! Welcome to this video on nucleic acids. In this video, we’ll cover what nucleic acids are and what they’re made of.

Nucleic Acid Structure

Nucleic acids are what make up our genetic material. To know how and why they go together to form structures like the famed DNA double-strand helix, it helps to understand their shape and what goes into them.

Nucleosides

To get started, the basic component of DNA and RNA is a nucleoside. This is made from a cyclic sugar and a nitrogenous base, bound by a glycosidic link. In DNA and RNA, this is a covalent bond between the 1′ nitrogen for pyrimidines or 9′ nitrogen in purines and the 1′ carbon in the sugar, either ribose or deoxyribose.

Nitrogenous Bases

In nucleic acids, the nitrogenous bases, also called nucleobases, are what pair up to form the base pairs. These pairs are formed between a purine and a pyrimidine. Pyrimidines are single carbon-nitrogen rings, while purines are pyrimidines fused to an imidazole ring to make a double ring.

The nitrogenous bases seen here have hydrogen bonding between each other, which holds the nucleic acid strand together.

Nucleotides

So now we know what makes up nucleosides, but we’re still short of having our nucleic acid. Next comes the phosphate group. When the sugar of a nucleoside is linked to one or more phosphate groups, you get a nucleotide. These are connected by an ester linkage — oxygen covalently bound between two chains (in this case, the phosphorus atom in a phosphate group and the 5’ carbon of a nucleoside, or even another phosphate group).

Sugar Phosphate Backbone

When our nucleotides are bound together from the 3’ carbon on one nucleotide’s sugar to the phosphate group on the 5’ end of a different nucleotide, we start forming a strand that is referred to as the sugar-phosphate backbone (of DNA and RNA). When our nucleotides are connected in a long chain like this, we refer to it as a nucleic acid — either DNA or RNA, but we’ll cover some differences on those shortly.

Nucleic Acid Structure

Now that we’re finally at nucleic acids, one important thing to note is how the nucleotides stack together. When the nucleic acids are connected at their base pairs, they don’t stay straight and rigid like a ladder, how we sometimes see nucleic acids illustrated to read base sequences — instead it naturally forms a helical structure, like a spiral staircase. This is its tertiary structure, the 3D form it takes as a result of everything it’s made from. This form leaves it the least open to water within the cell, by having two strands connected to the bases, and twisted to further reduce open space to water. Perhaps the most noticeable feature is that it’s not a symmetrical helix. The nucleic acids double helix features a major groove and a minor groove, referring to the larger and smaller gaps between the edges of the sugar-phosphate backbone. The major groove is where most activity takes place, like polymerases binding to create RNA templates, also known as messenger RNA (mRNA).

Nucleic acids in DNA vs RNA

So when talking about nucleic acids, there are just a couple of things to note. We first have to consider whether we’re talking about DNA or RNA. We learned that in general nucleic acids there are chains comprised of a nitrogenous base, a phosphate group, and a sugar. In DNA, that sugar is 2-deoxyribose, providing DNA its name: Deoxyribonucleic Acid. In RNA, that sugar is ribose, making it a Ribonucleic Acid. The difference between these two is the presence of a hydroxyl group on the 2-carbon in ribose, which is absent in 2-deoxyribose. Aside from the sugar used in its structure, there’s also one other important difference: the nitrogenous base. DNA uses thymine whereas RNA uses uracil, both of which pair with adenine.

Function of Nucleic Acids

So what role do these nucleic acids actually serve? We mentioned before that nucleic acids are the genetic material in our cells. How this works is that the order of bases (adenine, thymine/uracil, guanine, and cytosine) in nucleic acids creates a readable code, to be eventually turned into proteins. This process of taking a nucleic acid and making a protein is referred to collectively as transcription and translation. Transcription takes the DNA in our cells and unzips it, to create a matching strand of RNA. Translation is when the matching RNA strand is then transported to a ribosome where the bases are read in sets of 3 (or triplets) to bring specific amino acids to the ribosome, forming a chain of amino acids — the most basic structure of proteins.

I hope this video on nucleic acids was helpful. See you guys next time!

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