 In this video I will describe the building blocks, structure, and functions of nucleic acids, DNA, and RNA. Nucleic acids are polymers made of monomers called nucleotides. In the illustration on the left here we can see the basic structure of a nucleotide that has a phosphate region, a pentose sugar, and a nitrogenous base. Those three regions are all part of the one monomer of a nucleotide. Now there are different nucleotides depending upon either the nitrogenous base structure or the sugar structure, but the phosphate is not variable between the different nucleotides. Nucleotides are joined together by dehydration synthesis between the phosphate and sugar unit forming the long polymers known as nucleic acids. The major nucleic acids are DNA and RNA. One of the major differences between DNA and RNA has to do with the chemical structure of the sugar region of the nucleotide. The ribose sugar is found in the nucleotides of RNA. RNA stands for ribonucleic acid. And the deoxyribose sugar unit is found in DNA, which stands for deoxyribonucleic acid. Then the nitrogenous bases are four different types found in DNA, and we can see those four different types are shown as different colors in the illustration on the right. Adenine is shown in red, thymine is shown in yellow, guanine is shown in blue, and cytosine is shown in green. Now another major difference between DNA and RNA is that DNA is a double-stranded molecule. Two long nucleic acid polymers are held together by hydrogen bonding between the nitrogenous bases of the nucleotides. And the base pairing that forms hydrogen bonds is very specific, so that adenine will always form a base pair with thymine, and guanine will always form a base pair with cytosine. So here we can see the structure of the five different nitrogenous bases that are found in nucleic acid nucleotides. Cytosine, thymine, adenine, and guanine are all found in DNA polymers. In RNA, there is no thymine, but instead uracil will take the place of thymine. The other major difference we can see illustrated here is the structure of the deoxyribose found in the nucleotides of DNA, and ribose found in the nucleotides of RNA. DNA functions as the molecule that stores genetic instructions in the nucleus within animal cells. The genetic instructions are the sequence of the nucleotides within the DNA polymer. This information can be read by proteins that will then make RNA. The process of reading DNA to make RNA is known as transcription. And then the genetic message in RNA can then be used in order to make proteins. Or that genetic instructions of the RNA that came from the DNA is read, and that information is the information that guides the sequence of amino acids or the primary structure of a protein that's being made. So here we can see the structure of DNA has a double helix structure where there are two DNA polymers held together by hydrogen bonding between complementary base pairs, where thymine will form two hydrogen bonds with adenine, guanine will form three hydrogen bonds with cytosine, and because A or adenine always forms a base pair with T or thymine, and C cytosine always forms a base pair with G guanine, having just one polymer, just one strand of the DNA double helix contains all of the genetic instructions, all of the same information is found on just one strand, and the second strand is essentially a copy of that information. During DNA replication to prepare for cell division, one strand of DNA will serve as the template for the synthesis of a new DNA strand, so that each of the daughter cells will inherit a complete copy of the genetic instructions. So having the double-stranded structure of DNA enables this mechanism of DNA replication to enable cell division. This structure also helps to stabilize the DNA, the DNA's double helix structure as well as the deoxyribose is just a more stable chemical structure compared to RNA, and it's good to have a very stable structure to store our genetic instructions because anything that disrupts the structure of our DNA can be a mutation that could lead to a change in proteins that are produced and ultimately disrupt the functions of the cell. Not all nucleotides are used to make the nucleic acid polymers. Some nucleotides have distinct functions. Here's an example of adenine where the basic structure of the nucleotide has extra phosphate groups attached. These phosphate groups that are linked together are held together by very high energy bonds. This is because each of the phosphate groups has a negative charge, and the negative charges repel one another. This is analogous to a spring that has been tightly compressed. When the pressure is released, a large amount of energy can be released as the spring uncoils, or in this case as the high energy bond between the phosphates is broken. A large amount of energy is released. The chemical structure that we see here is commonly just abbreviated ATP, the full name adenosine triphosphate. ATP has three phosphates. If one phosphate is released, then ATP is converted to ADP, adenosine diphosphate. One more phosphate could be released, and ADP would be converted to AMP, or adenosine monophosphate. Another example of a nucleotide that doesn't form nucleic acids but has an important function in metabolism is NAD. NAD is nicotinamide adenine dinucleotide, and we will see as we study the mechanism of cellular respiration that NAD can accept electrons along with a hydrogen to become NADH. And then NADH can release those electrons and hydrogen ion as it's converted back to NAD+. And so the NAD and NADH molecules function as a way to transport high energy electrons within a cell.