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Eukaryotic Cells

Teacher/Instructor Patrick Roisen
Patrick Roisen

M.Ed., Stanford University
Winner of multiple teaching awards

Patrick has been teaching AP Biology for 14 years and is the winner of multiple teaching awards.

Eukaryotic cells are more complex than prokaryotic cells. Eukaryotic cells are found in most of the more complex kingdoms of life including fungi, animals, plants and protists. Eukaryotic cells have internal membranes around their nuclei and organelles and cytoskeletons. Plant cells also have cell walls, but these are not present in other types of eukaryotic cells.

Eukaryotic cells are one of the two major kinds of cells in the world of Biology. Now their name actually gives you their key characteristic cause "Eu" means true or good, "kary" means nucleus and that ties into the basic characteristic for all eukaryotic cells is that they have an organelle within the cell itself that has its own membrane and that is the nucleus. Now most eukaryotic cells also have mitochondria and those that can do photosynthesis will have the membrane bound organelle called the chloroplast.

Now another thing that generally all the eukaryotes have is that they hav4 many DNA molecules or chromosomes and because they have so much DNA in order to fit into the small space inside of the nucleus, they have to wrap those DNA molecules around specialized proteins called histones and that means that a DNA molecule which in eukaryote is linear has to be wrapped or bound on these histone proteins.

Lastly they have their own special kind of ribosomes that different from the prokaryotes and generally you could just call them eukaryotic style ribosomes. Now the two most common kinds of eukaryotic cells are the animal cells and the plant cells.

Now I know in this diagram the labels are kind of hard kind of small and hard to see but let's focus in on some the key things that you'll see in an animal cell. You'll see it has the membrane around it with the nucleus that has you can see its own membrane wrapped around it. The other key eukaryotic organelle here is the mitochondria, now animal cells differ from plant cells in that they also have these things here, these two barrel shaped things that are 90 degrees to each other, those are called centrioles and a common question on a Biology test is to try to identify organelles that are unique to animal cells and the answer would be centrioles. Now I'm going to let you know one of the trick questions. The trick question is they'll also include an option where you can choose centrioles and mitochondria because most kids know that plants do photosynthesis so of course they could be using chloroplast and animal cells break down sugar from photosynthesis in order to get the energy and that's done by the mitochondria, so a lot of kids will think plants have chloroplast only animal cells have mitochondria and that's not true.

If we take a look at this plant cell you can see it has mitochondria why? Because just like you, it wants to get the energy that's in the sugar that came from photosynthesis. Now photosynthesis is done by that cell there oh! Sorry that organelle there called the chloroplast and you can see it has its own double membrane around it just like the mitochondria has two membranes in and out of it. Now something else that makes a plant cell different from an animal cell is that plant cells have this large thick cell wall wrapped around them to give them the structure and stability that animal cells don't need remember animal cells are all about moving so they don't need a plant cell wall around them cause that would keep them boxed in and what do we use for structure and stability? Our own skeleton so whether you're insect and you wear your skeleton on the outside or you're jelly fish and you use water that's on the inside of you as a hydrostatic skeleton. We have our own structural support built in to the entire body we don't need every cell to have its own skeleton.

Another characteristic you'll commonly see in plant cells is that they'll have this large vacuole and that's usually filled up with water and that's how they are able to get all filled and it's called turgid and if the water in the water vacuole starts to leak out that's when a plant cell will start to wilt and the entire plant will start to deflate and wilt as well. That's eukaryotic cells.