Introduction to DNA

DNA which stands for deoxy ribbo nucleic acid is a very important biological molecule whose function is to store the genetic information that is found within the cell so the cell including eukaryotic and procaryotic cells can use the DNA molecules to synthesize proteins and enzymes that are necessary for the cell survival in fact whenever our cell or organism reproduces each indiv idual cell must replicate the DNA molecule and pass it down to The Offspring now what exactly is the composition of DNA so in the same way that proteins consist of individual units known as amino acids DNA molecules are also polymers meaning they consist of individual subunits known as nucleotides and any given nucleotide consist of three parts so we have a deoxy ribo sugar which is a five membered sugar we have a nitrogenous base and we also have our phosphate group now what exactly is the structure or arrangement of these three different types of uh sections or groups within our nucleotide so this is one example of a nucleotide we have our base the nitrogenous base attached to our Center sugar which is also attached to our phosphate group now there are four different types of nitrogenous bases we have adamine guanine cytosine and thyine now adenine and guanine or simply A and G are two types of nitrogenous bases that consist of two rings and these types of nitrogenous bases that consist of two rings are known as purines and notice thyine and cytosine or TNC consist of only a single ring structure and these types of nitrogenous bases are known as peridin so let's look at the arrangement of our nucleotide and how the nucleotides bond to one another so remember in a protein we have amino acids that bond to one another vehicle veent bonds known as dipeptide or peptide bonds in the case of DNA the individual subunits known as nucleotides bond to one another via Bond known as a phospho diaster bond so let's take a look at the following molecules so we have one nucleotide and a second nucleotide and notice that these two nucleotides bond to one another via the phosphodiester bond so we have the phosphorus atom and we also have the two eser bonds shown here and that's exactly why it's called a phosphodiester bond now notice that the bonding takes place between the third carbon of one sugar and the fifth carbon of the second sugar and that's exactly why this is called a 3 to five Bond so this is our phospho Di Bond so notice that because there are four different types of nitrogenous bases that means there are four different types of nucleotides and it is very common to call our nucleotide by the type of uh nitrogenous base that it contains so for example because this nucleotide contains the guanine nitrogenous base we simply call the nucleotide the guanine and because this contains the adenine nitrogenous base this nucleotide can be called simply the adenine nucleotide so we have one nucleotide bonds to a second nucleotide via this phosphodiester Bond now DNA in cells specifically in human cells doesn't actually exist as a single strand of DNA in fact two strands of DNA that are complementary to one another actually bind to form a double stranded DNA and that double stranded DNA forms a coil that we call the double helix and the two singl stranded dn's bond to one another via a special type of dipole dipole Bond known as hydrogen bonds so the thing that holds our two strands of DNA together to form our double Helix are hydrogen bondings or hydrogen bonds between adjacent or opposite nucleotide specifically our nitrogenous basis so we have this nucleotide which is right next to this nucleotide and the bonding takes place between our adjacent or complementary nitrogenous bases so guanine always forms hydrogen bonds with cytosine while our adenine always forms hydrogen bonds with our thyine and notice in the case of guanine and cytosine we have three hydrogen bonds and in the case of Adine and thyine we only have two of these hydrogen bonds so that means the guanine cytosine pair forms a more stable attraction than our adenine thyine so if a if a given DNA molecule Ule contains more guanine cytosine pairs that means the bonding between our two single stranded DNA molecules is stronger now one other important thing that we have to mention about the double helix is the directionality of our single stranded DNA so let's take a look at this single stranded DNA that only consists of two nucleotides so we have the guanine the adenine notice that the guanine begins on our five carbon and it goes down to our three carbon while the second single stranded DNA begins with the third carbon and goes down to the fifth carbon and this type of opposite or reverse Arrangement is known as anti-parallel that is the two single stranded DNA this one and this one run in the parallel Direction but they run in the opposite direction meaning that this goes from the five to the three carbon and this runs from the three to the five carbon so once again we have our notice that if the first trand runs in a 53 Direction then the complementary strand must run in the reverse 3 to five Direction and this type of arrangement is known as anti-parallel and the reason the two DNA molecules run anti-parallel is to ensure that the bonding between our nitrogenous bases is exactly right so that we create strong bonds between our two DNA molecules and so that our double stranded DNA molecule basically doesn't unzip itself spontaneously so this is a slightly better description of our DNA molecule because this shows our double helix structure so we have the blue and our purple strand so the the blue one begins at the five end and goes all the way to the three end while the pink begins at the 3 end and goes all the way to the five end and this is what we mean by the anti-parallel directionality where one of our single stranded DNA runs from the five to three while the other one runs from the 3 to five now one other thing that we have to notice is that the sugar as well as the phosphate within our double stranded DNA points outside of that DNA while inside that double stranded DNA double helix structure we have our nitrogenous bases so that is shown by the following diagram so this line basically represents the sugar and the phosphate while these squares represent our nitrogenous bases and our nitrogenous bases are basically protected and are found inside our double stranded DNA molecule and that means our bonds can form and those bonds are not dis uh disrupted by any type of outside force that is found on the outside of that double stranded DNA molecule of course if we for example increase the temperature eventually a temperature will be reached where these bonds will break regardless of the fact that our nitrogenous bases are found inside that DNA molecule so once again DNA is basically a polymer molecule that contains nucleotides and any given nucleotide consists of three three sections we have the sugar the nitrogenous base and our phosphate group and there are four different types of nitrogenous bases the purines are adenine and guanine while our peridin are thyine and cytosine now the way that our two anti-parallel singles strand the DNA's bond together is via hydrogen bonds between our adjacent Nitro nitrogenous bases so so guanine nitrogenous base always forms bonds with cytosine while adamine always forms bonds with thyine and notice that the way our individual nucleotides in any singl stranded DNA form our bonds is via these special types of bonds known as phospho diester bonds

Channel: Andrey K

Views: 304,535

Keywords: deoxyribonucleic acid, DNA, introduction to DNA, nucleotides, adenine, guanine, cytosine, thymine, nitrogenous bases, phosphodiester bond, phosphodiester linkage, pyrimidines, purines, antiparallel, double helix, DNA double helix, DNA structure, DNA composition, deoxyribose sugar, DNA molecules, summary of DNA

Id: sLdJTcBnO3c

Length: 10min 53sec (653 seconds)

Published: Fri Sep 05 2014