[Music] hi and welcome back to free science lessons by the end of this video you should be able to describe the general structure of eukaryotic cells okay now the first key idea you need to understand is that we can divide all living organisms into two categories these categories are eukaryotes and prokaryotes animals plants and fungi are all examples of eukaryotic organisms prokaryotes include bacteria and archaea in this video we're looking at eukaryotes and in the next video we'll be looking at prokaryotes so what are the key features of eukaryotic cells I'm showing you here the general structure of a typical animal cell in all eukaryotic cells the DNA is contained in a membrane-bound nucleus and the words membrane bound means surrounded by a membrane now we're going to be looking at the structure of the nucleus in much more detail in a later video and what you'll see is that the nucleus actually has a double membrane now strictly speaking some eukaryotic cells can lose their nucleus as they develop for example red blood cells in humans but the vast majority of eukaryotic cells have a nucleus throughout their lifespan so having their DNA in a membrane-bound nucleus is a key feature of eukaryotic cells the second key feature of eukaryotic cells is that their DNA is tightly wrapped around proteins called histones and together the DNA and histone proteins form chromosomes by tightly coiling their DNA into chromosomes eukaryotic cells can pack a great deal of DNA into their nucleus another key feature of eukaryotes is that their DNA is a linear molecule and the word linear means that the ends of the DNA molecule in a chromosome are not joined together to form a loop now we've already seen that eukaryotic cells have a membrane-bound nucleus but they also contain a number of other membrane-bound organelles for example we find mitochondria the Golgi apparatus and the endoplasmic reticulum and all of these organelles are membrane-bound we find the same organelles and plant cells but in plant cells we also find chloroplasts and evacuol and these are also membrane-bound organelles so the presence of membrane-bound organelles is another key feature of eukaryotic cells and we'll be taking a closer look at all the membrane-bound organelles in later videos now eukaryotic cells also contain other organelles that are not membrane-bound and a good example of ribosomes which are involved in protein synthesis we also find ribosomes and prokaryotic cells but the ribosomes in eukaryotic cells are larger than those in prokaryotes scientists say that eukaryotic cells contain ATS ribosomes and the letter s is simply a unit showing how quickly organelles move in a centrifuge now as you can see eukaryotic cells are surrounded by a cell surface membrane and this helps to control the molecules that can pass in and out of the cell but in plants and fungi the cell membrane is surrounded by a cell wall the cell wall helps to maintain the structure of these cells in plant cells the cell wall is made of the polysaccharide cellulose and in fungi the cell wall is made from the polysaccharide chitin but you need to remember that animal cells do not have a cell wall in the next video we look at the key features of prokaryotic cells foreign [Music]