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Course: MCAT > Unit 6
Lesson 4: Eukaryotic cellsCharacteristics of eukaryotic cells
Eukaryotic cells, found in multicellular organisms, are defined by their compartmentalization into organelles, each with a unique function. The nucleus, a key organelle, houses genetic material. Other organelles include mitochondria, endoplasmic reticulum, Golgi apparatus, lysosomes, and peroxisomes. Eukaryotic cells divide through mitosis, a more complex process than prokaryotic binary fission.
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Visit us (http://www.khanacademy.org/science/healthcare-and-medicine) for health and medicine content or (http://www.khanacademy.org/test-prep/mcat) for MCAT related content. These videos do not provide medical advice and are for informational purposes only. The videos are not intended to be a substitute for professional medical advice, diagnosis or treatment. Always seek the advice of a qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read or seen in any Khan Academy video.
Want to join the conversation?
- Which of the following transcriptional control features are found in both prokaryotes and eukaryotes?
a. Introns
b. Promoter repressors
c. 5’ methyl-G capping
d. Differential splicing
The answer is b, but why are introns special to eukaryotes? Why is 5' methyl-G capping special to eukaryotes? Why is differential splicing special to eukaryotes?(4 votes)- Think about the differences between prokaryotic and eukaryotic cells and the differences in their processes... transcription and translation are (or can be) simultaneous for prokaryotes. How would splicing work with such a process? The methyl cap protects against degradation during transport out of the nucleus before translation... again, prokaryotes have no need for that.
You may want to review these videos on replication:
https://www.khanacademy.org/test-prep/mcat/biomolecules/dna/v/transcription-and-mrna-processing
https://www.khanacademy.org/test-prep/mcat/biomolecules/dna/v/differences-in-translation-between-prokaryotes-and-eukaryotes(1 vote)
- At5:32it says "Respiration where glucose is converted into ATP." What is ATP?(2 votes)
- ATP -> Adenosine Triphosphate
It is the energy currency of the cell.(2 votes)
- At5:56, is endoplasmic reticulum just folds of membrane, or is there anything within the membrane? And are smooth endoplasmic reticulum and rough endoplasmic reticulum always together like that? Thanks!(3 votes)
- E.R and Rough E.R are a same structure with two different parts, one with ribosomes attached and the other one without ribosomes. E.R also enfolds protein, translated by ribosomes attached on the rough e.r, inside a membrane to be taken to Golgi apparatus.(0 votes)
- If Eukaryotic organelles lack intelligence of their own, how do they "know" where an item it produces is required to go? For example, how does the endoplasmic reticulum know to send proteins to the Golgi apparatus and not a mitochondrion? True, a routine may have developed for particular chemical creations, but doesn't it need to know the first time around?(2 votes)
- whats the difference between lysosomes and perixosomes?(2 votes)
- Where do these names come from? Do some come from Latin?(2 votes)
- Is the nucleus the biggest part of a cell?(2 votes)
- what does membrane bound mean?(2 votes)
- Between the Prokaryotic cells and the eukaryotic cells, Which are more active and which can survive at any environment(climate,nutrition,habitat)(2 votes)
- What is the difference of Eukaryotic cells and Akaryote?(2 votes)
Video transcript
- [Voiceover] All living
things are made of cells. And humans and all multicellular organisms are made of a type of cell called eukaryotic cells. But what is it that
makes a cell eukaryotic? To answer that question, let's look at the two major types of cells. On the left is a prokaryotic cell, and on the right is a
diagram of a eukaryotic cell. So let's define eukaryotic cells as how they're different than prokaryotic cells. So usually, eukaryotic
cells are much larger than prokaryotes, and they're also, eukaryotic cells are also found in multicellular organisms, although there are single
cellular eukaryotes such as certain protists. But what are the defining characteristics that make a cell eukaryotic? The most important thing
that eukaryotic cells possess that prokaryotes don't is the idea of compartmentalization. This is kind of a big word, but essentially, what it means is that the cell is divided
into different compartments. And we can see some of these compartments drawn here on the right
in our eukaryotic cell, whereas our prokaryotic
cell doesn't appear to have many different compartments. But why is it that a eukaryotic cell has lots of different
compartments within it? Well, I kind of think of
it as rooms in a house. So if you have lots of
different rooms in a house, each room can do something different. So you could have a living
room, and a kitchen, and a dining room, and a
bathroom, and a bedroom. And they all have a different function. Prokaryotic cells then would be like a one-room house where everything is in a single room. And you could see that this single room has to be able to do everything. So the compartmentalization
of the eukaryotic cell into different compartments
or kind of rooms allows each different compartment to have a different function. And this is really
important in the complex needs of the cells. The name for these compartments in the eukaryotic cell is organelles. Just like your body has different organs that have different functions, your heart pumps blood, your lungs take in oxygen, different organelles in the cell have different functions. And these organelles are separated from other parts of the cell by membranes. And the name "eukaryotic" comes from one of these organelles. The word "eu" means "well" in Greek, and "karyote" means "kernel" or "nut." So when scientists originally looked at eukaryotic cells, they
saw a very well-formed circular object in the center that looked kind of like a nut. And so, they called
these cells "eukaryotes" because they had a well-formed nut in the center of the cell. This nut is what we now
know as the nucleus. The nucleus is a circular membrane-bound organelle that contains
all of the genetic material in the cell. So all of your chromosomes
are inside the nucleus. This separates them from
the outside of the cell. The nucleus is the defining organelle of eukaryotic cells. In contrast, prokaryotic cells have their genetic material as
well as everything else in the cell just kind of floating around all in one big space. And so, in prokaryotes,
to divide and become new cells, all they have
to do is make two copies of everything, and then
split down the middle in a process called binary fission. But in eukaryotes, we can see that because the cell has
all of these different compartments or
organelles, there is a more complex way to divide into a new cell. And the process that eukaryotic cells use to divide is called mitosis. So these are the defining characteristics of eukaryotic cells that sets them apart from prokaryotic cells. They're compartmentalized into different membrane-bound organelles, the most important of which
is called the nucleus, which is responsible for
the name "eukaryotic." And finally, they divide
by the process of mitosis. Let's go through some
of the other important organelles within eukaryotic cells. So first, let's go back to the nucleus. And the nucleus, I kind of think of as the control center of the cell because that's where all of the DNA is, and where DNA is transcribed into mRNA. Probably the next most important organelle in the body are called mitochondria. Mitochondria, you can think of as the cell's power plant because mitochondria
is the site of cellular respiration where glucose
is converted into ATP to provide the energy for
everywhere else in the cell. The next organelle we'll look at is called the endoplasmic reticulum. And so surrounding the nucleus are dozens and dozens of folds of membranes in this really complex pattern. But the unique thing about it, inside these folded membranes is it's all continuous,
so it all encloses one single compartment,
even though the membrane is folded back and forth on itself lots and lots of times. And the endoplasmic reticulum is primarily the site of protein synthesis. mRNA, which is transcribed from DNA in the nucleus, is translated at the endoplasmic reticulum. So I think of the endoplasmic reticulum as the factory of the cell where proteins are produced. After these proteins are produced, they are sent to another
organelle that also has kind of a lot of folded
membrane structure, but it's not a continuous compartment like the endoplasmic reticulum. And this organelle is
called the Golgi apparatus. And the Golgi apparatus is kind of like the mail room of the cell. So proteins that are produced in the endoplasmic reticulum are sent to the Golgi apparatus, and the Golgi apparatus is able to send those proteins to other parts of the cell, depending on where that
protein needs to go. So if the protein needs to
be secreted by the cell, the Golgi apparatus sends
it to the outer membrane of the cell and releases it. If it needs to go to
a different organelle, the Golgi apparatus can
send those proteins, as well as other
biological macromolecules, to those sites as well. The last two organelles to mention are the lysosome and the peroxisome. And cells can have multiple
ones of each of these, but I mentioned them
together because they both have a similar structure. They're kind of a spherical organelle enclosed by a single plasma membrane. And the environment inside the lysosomes and the peroxisomes is very different from the environment outside
in the cell's cytosol. And so the lysosomes and peroxisomes are kind of like recycling
centers in the cell. That's because when cellular components are no longer functional and need to be broken down, they're
trafficked to the lysosome where they are broken down into their more basic components that
can be reused to rebuild new proteins or other macromolecules. The peroxisome has a similar function to the lysosome, but it's
a little bit different because in the peroxisome
is the site where reactive oxygen species like peroxides are reduced into nontoxic forms. So these are the main organelles of the eukaryotic cell, which we remember is defined by the
compartmentalization of the cell into different membrane-bound organelles.