Microbiology, part 32: Genetics - Nucleotides & DNA Structure

Hi, I'm Cathy with Level Up RN. In this video, I'm going to begin my coverage of topics from the Microbial Genetics section of our Level Up RN microbiology flashcard deck. Specifically, I'll be talking about nucleotides and DNA structure. At the end of the video, I'm going to give you guys a little quiz to test your knowledge of some of the key facts I'll be covering. So definitely stay tuned for that. And if you have our flashcards, go ahead and pull out your flashcards on nucleotides and DNA structure so you can follow along with me, and pay close attention to the bold red text on the back of the cards because those are the things that you are likely to get tested on in your micro class.

DNA is a nucleic acid, and nucleotides are the building blocks of nucleic acids. Each nucleotide is composed of a five-carbon sugar, a phosphate group, and a nitrogenous base. In DNA, the five-carbon sugar is deoxyribose, whereas in RNA, the five-carbon sugar is ribose. The carbon atoms in a deoxyribose molecule are numbered 1 prime, 2 prime, 3 prime, 4 prime, and 5 prime. The 1 prime carbon is connected to the nitrogenous base. The 3 prime carbon is connected to the hydroxyl group and is used to attach to the next nucleotide in the chain. And then the 5 prime carbon is connected to the phosphate group and is used to attach to the previous nucleotide in the chain.

The four nitrogenous bases in DNA include adenine, guanine, cytosine, and thymine. Adenine and guanine are purines, which each have two carbon-nitrogen rings, whereas cytosine and thymine are pyrimidines, which each have one carbon-nitrogen ring. Of note, in RNA, uracil replaces thymine. So the nitrogenous bases in RNA include adenine, guanine, cytosine, and uracil.

Now that you understand the components of a nucleotide, let's talk about how they combine to form a nucleic acid strand. So nucleotides are joined by phosphodiester bonds between the three prime hydroxyl group of one nucleotide to the five prime phosphate group of the next nucleotide. This forms a nucleic acid strand with alternating sugar and phosphate molecules, which is referred to as the sugar-phosphate backbone. And of note, new nucleotides are always added to the three prime end of the nucleic acid strand.

DNA consists of two nucleic acid strands that are anti-parallel, meaning that one strand runs in the five prime to three prime direction, whereas the other strand runs in the three prime to five prime direction. The two strands of DNA wind around each other to form a double helix, which resembles a twisted ladder. The rungs of the ladder are formed from base pairing or hydrogen bonding between specific purines on one DNA strand to specific pyrimidines on the other DNA strand. So adenine always base pairs with thymine. So adenine and thymine are complementary base pairs, whereas cytosine always base pairs with guanine. So cytosine and guanine are also complementary base pairs.

All right, it's quiz time, and I have five questions for you. You guys ready? Question number one. What are the three key components of a nucleotide? The answer is a five-carbon sugar, a phosphate group, and a nitrogenous base. Question number two. The backbone of DNA consists of alternating blank and blank molecules. The answer is phosphate and sugar molecules. Question number three. What kind of chemical bonds form between purines on one DNA strand and pyrimidines on the other DNA strand? The answer is hydrogen bonds. Question number four. Adenine always base pairs with blank. The answer is thymine. And question number five. In RNA, blank replaces thymine. The answer is uracil.

All right. That's it for this quiz. Hope you did great, and I hope you found this video to be helpful. Take care and good luck with studying.

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The carbon atoms in a deoxyribose molecule are.