every single eukaryotic cell contains the nucleus the nucleus is a membrane enclosed organel that contains stores protects and expresses most of the genetic information that is found in our cell the DNA the deoxy ribonucleic acid the reason I say most and not all is because actually a small portion a small portion of the DNA is found in the mitochondria which is another membrane enclosed organel found in our body and we'll discuss that when we look at the mitochondria in its structure in this lecture we're going to focus on the structure and the composition of the nucleus of the eukaryotic cell so let's begin by discussing the envelope the region that basically encloses our nucleus this is known as the nuclear membrane or the nuclear envelope so just like the entire UK care perodic cell contains our cell membrane the nucleus contains a membrane known as the nuclear membrane and the nuclear membrane just like the actual cell membrane also consists of a lipid by layer so we have an inner as well as an outer region of the membrane that basically looks something like this so we have the outer membrane region that consists of the hydrophilic heads and the hydro phobic tails and we have the inner membrane region that also consists of our hydrophilic heads and the hydrophobic tails and the space the fluid space between these two regions the outer and the inner membrane is known as the perinuclear space now throughout the entire nuclear envelope throughout the entire nuclear membrane we have very tiny holes known as nuclear pores that basically allow materials to move into the nucleus as well as outside the nucleus and we'll discuss exactly what the nuclear por is in just a moment now the outer membrane is actually physically connected to the membrane of the rough endoplasmic reticulum and this is important because when we synthesize our RNA ribosomal RNA we have to have a quick way to transport our RNA from the nucleus to our endoplasmic reticulum and that's why they are connected so the inner membrane so this is the outer membrane that is found uh on the side of our cytoplasm but the inner membrane is found on the side of the fluid found inside our nucleus and the fluid inside the nucleus is known as the nucleoplasm so the nucleoplasm is the fluid in inside the nucleus the cytoplasm is this entire region found between the cell membrane and our nuclear membrane now the inner membrane is also covered by a network of proteins known as intermediate filaments that extend throughout the entire nucleus as shown by these extensions here now these Network or this network of extensions of intermediate filaments found inside the nucleus is known as the nuclear lamina and the nuclear lamina basically plays the role of stabilizing the structure of the nucleus as a whole and they are also involved in gene expression now let's return to what a nuclear pore is so earlier we said that the entire nuclear membrane contains these holes known as nuclear pores but what exactly is a nuclear pore well a nuclear pore is not exactly an empty hole nuclear pores are actually protein complexes that extend throughout the entire nuclear membrane and these protein complexes help transport biomolecules such as RNA ribosomal units ribosomal proteins as well as polymerase between our nucleoplasm and our cytool the cytoplasm this region here of our eukaryotic cell now a polymerase is basically a type of enzyme a type of protein that plays an important role when we translate replicate or when we transcribe our DNA molecules and we'll discuss that when we discuss replication translation as well as transcription now let's move on to region of the nucleus known as the nucleis so at the heart of any nucle nucleus of any eukariotic cell is a region known as the nucleis and it takes up about 25% of space found inside that nucleus now this is a very important section because within this section we have RNA molecules and proteins that are responsible for synthesizing our RNA or ribosomal RNA that is needed to create ribosomes found within the endoplasm reticulum as well as inside our cytool of the cell finally let's discuss the composition of DNA inside the nucleus so earlier we said the entire purpose of the nucleus is to store protect and express our genetic information the DNA the deoxy ribonucleic acid now the problem is the linear version of DNA is extremely long in fact if we take a single DNA molecule found inside the human cell and we extend it in a linear fashion it will be over 5T long and that's extremely long so actually what happens inside the nucleus is we take our linear DNA and we wind it around special proteins known as histones and then we basically take the histones we connect those hones and we coil them further to create a structure known as as the chromatin which is a very very condensed version of our linear DNA so inside the nucleus the linear DNA is wound around special structural proteins called histones combining eight histones forms a structure known as the nucleosome and these nucleosomes can be wrapped into coils and super coils of complexes of protein DNA and RNA called chromatin now when the DNA is not actually being used when we are not transcribing our DNA molecule it exist in this condensed super coiled form however to actually read and express to actually transcribe our DNA molecule we have to uncoil that section of the DNA and at any given time in the nucleus of our cell only a small percentage of the DNA is actually Unwound it exists mostly predominantly in the condensed and super coiled chromatin stage