Prokaryotic and eukaryotic cells
Eukaryotic cells contain membrane-bound organelles (such as the nucleus and mitochondria), while prokaryotic cells do not. DNA in eukaryotic cells is found inside the nucleus, while DNA in prokaryotic cells is located in the cytoplasm. Eukaryotic cells are generally larger and more complex than prokaryotic cells. Eukaryotic organisms include animals, plants, fungi, and paramecia. Prokaryotic organisms include bacteria and archaea.
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- so at1:20, prokaryotes don't have a nucleus? Or just no membrane bound nucleus?(18 votes)
- A Prokaryotic cell doesn't have a membrane bound nucleus but it has a nucleoid which is like a nucleus without a membrane. Hope I helped.(30 votes)
- What is the difference between archaea and bacteria?(17 votes)
- Archea have three RNA polymerases like eukaryotes, but bacteria have only one. ... Archaea have cell walls that lack peptidoglycan and have membranes that enclose lipids with hydrocarbons rather than fatty acids (not a bilayer).(10 votes)
- Hello, thanks for the video. At4:27you mentioned that Eukaryotes have multiple single strands of DNA. Is this, in fact, a single-stranded or double-stranded DNA? DNA is usually a double-helix, right? What about the DNA in procaryotes? Is it single-stranded or double-stranded? Does it depend on the stage of cell-division cycle? Thank you for the answer!(11 votes)
- That section of this video was poorly worded.
The genomic DNA for both prokaryotes and eukaryotes is predominantly double-stranded — i.e. the DNA is mostly in the form of a double-helix. The multiple strands being described are chromosomes each of which contains a double-stranded DNA.(10 votes)
- so... is a red blood cell a prokaryotic cell? I ask this because the red blood cell- as far as I know- does not have any mitochondria?(5 votes)
- Definitions can often be a bit tricky, but it would be confusing§ to classify RBCs† as prokaryotic.
RBCs are derived from eukaryotic cells, so they are eukaryotic. In many ways they aren't "real cells", but are instead structures derived from cells. However, that is a really cumbersome phrasing, so we all just call them cells anyway.
There is KhanAcademy material on RBCs here:
§maybe this is a helpful analogy:
Imagine you met someone who had lost their arms and legs. Would you describe that person as a snake because they were a limbless land-dwelling vertebrate?
†Note: We are actually only discussing mammalian red blood cells, since the red blood cells in other vertebrates retain their nuclei and mitochondria.(14 votes)
- 1. So, basically, prokaryotes are OLDER versions of the cell? If the name "prokaryote" means "before nucleus", then wouldn't that mean that eukaryotes are newer versions of cells?
2. Is there no such thing as a multicellular prokaryotic organism? Or is it that organisms that are multicellular HAVE to be eukaryotic as well?(6 votes)
- 1. Evidence from both the fossil record and the structure of modern cells proves that prokaryotes existed long before eukaryotes. There is also something called the endosymbiosis theory which postulates that the mitochondria of eukaryotes evolved from an aerobic bacterium (probably related to the rickettsias) living within an archaeal host cell
and that the chloroplasts of red algae, green algae, and plants evolved from an endosymbiotic cyanobacterium living within a mitochondria-containing eukaryotic host cell.
2. There are lots of unicellular eukaryotes, including amoebas, paramecium, yeast, and so on. As to whether there are multicellular prokaryotes, the standard answer is No, but there is a lot of evidence that some bacterial species can aggregate together and divide labor so that the "colony" is working more efficiently.(11 votes)
- Do bacteria have only one chromosome?(3 votes)
- They often have one or two circular chromosomes, but several do not.(5 votes)
- Who was the first to think that we are made of cells(3 votes)
- Actually, it was Theodor Schwann who discovered that animals are made up of tons of cells. Robert Hooke coined the term "cell." He was examining the cork of a wine bottle and saw box-like compartments that reminded him of tiny rooms or "cells."(3 votes)
- What is the "chromatin form"2:36?(3 votes)
- Chromatin is a substance within a chromosome consisting of DNA and protein. The major proteins in chromatin are histones, which help package the DNA in a compact form that fits in the cell nucleus. Changes in chromatin. structure are associated with DNA replication and gene expression.(3 votes)
- thank you for this video but I have a question how small is a eukaryotic cell(3 votes)
- That depends on the organism, the cell type (in multicellular organisms), and developmental stage!
There is enormous variation in cell size within organisms.
This is pretty helpful for getting an idea of scale:
For example within humans there is a large variation in cell sizes — e.g. an egg cell is more than 100,000 times larger than a sperm:
This KhanAcademy page is also relevant:
- Are red blood cells considered prokaryotic cells since they don't have a nucleus?(2 votes)
Red blood cell or Erythrocyte is one of the formed elements formed in the red bone marrow. Each of the formed elements has specialised cell structure for performing specialised functions. As you might be knowing, the main function of RBC is to carry oxygen and carbon dioxide (in meager amounts). Haemoglobin, a conjugated protein made up of 4 globin subunits (both alpha and beta); is the main respiratory pigment of our body. Now, to accommodate this pigment within the RBC, it tends to lose all vital cell organelles including the nucleus. So, you can RBC as eukaryotic by origin but you can never call it prokaryotic. Prokaryotes have undefined nucleus; but the point is they have NUCLEUS. Mature RBC and sieve tube cells in plants are contrary to the cell theory proposed by Schleiden and Schwann. A better term for RBCs would be akaryotic, meaning “without nucleus”.
Hope that helps 😊(2 votes)
- [Voiceover] When we wanna categorize life as we know it at a very high level, we can categorize it as either eukaryotic, eukaryotic or as a eukaryote, eukaryote, or as a prokaryote, prokaryote. And the largest distinction between a eukaryote and a prokaryote are membrane-bound structures that eukaryotes have that prokaryotes don't have. The most noticeable of which is a membrane-bound nucleus. So in a eukaryote, the genetic information is going to be inside a membrane-bound nucleus. So this right over here, this is the nucleus. This is the nucleus and you have your genetic information inside it, you have your DNA. Here, for a prokaryotic cell, you're going to have your DNA. It might be bundled up into a section of the cell. We would call that a nucleoid but it's not membrane-bound. So let me we write this down no membrane... Let me write a little membrane-bound, membrane-bound nucleus. But that's not the only distinction in between eukaryotes and prokaryotes. It's almost the one that's most noted. In fact, the word eukaryote, the karyote part comes from the Greek for nut or kernel. So let me make this clear. So this is referring to a nut or a kernel while prokaryote means before the nut or kernel. So we don't see and you know, I just could think of the nut or the kernel as the membrane-bound structure, especially the membrane-bound nucleus over here. But that's not all. Eukaryotes will also have other membrane-bound structures that you will not see in prokaryotes. For example, you will tend to see mitochondria, mitochondria, in a eukaryotic cell, both plant and animal cells, but you won't see it in a prokaryotic cell. And there's other types of membrane-bound structures. You could see things like Golgi apparatus. This over here is a micrograph of a eukaryotic cell. And you see the Golgi apparatus, right over here, which helps package proteins. You see a micrograph of mitrochondria. This is a micrograph of the nucleus. So this, right over here, is the nuclear membrane. And then you see all the genetic information. It's all spread out. It's in chromatin form right over here but you see it's especially densely packed right over here. And we've also put it in this and right over there. So this is all the DNA in chromatin form but this part that looks extra dense or dark in this micrograph right over there, we call that the nucleolus. We call that the nucleolus. And we now know that this is where ribosomal RNA is being produced. And ribosomal RNA, that forms part of the structure of ribosomes which are essential in the translation, well I guess you can say, the construction of proteins based on the information in mRNA. We'll go into a lot more depth in that in other videos. So these are ribosomes right over here and they're made up of ribosomal RNA and they're also made up of proteins. And so this nucleolus over there, that's where that's happening, that denser part of the nucleus. So the key distinction, eukaryotic cell, you have a membrane-bounded nucleus, you have other membrane-bound structures like mitochondria. In fact, there's some theories that mitochondria first evolved as prokaryotic organisms that eventually lived in symbiosis inside of a larger eukaryotic cell. And then the other distinction is that in eukaryotes, the DNA tends to be in multiple strands. So the DNA, if you were to kinda straighten it out, it would be in multiple strands. On a prokaryote, the DNA tends to be circular. It can be all flipped around and whatever else but at the end of the day, it would be circular DNA. So those are the three core distinctions: nuclear membrane, other membrane-bound organelles, like mitochondria and the Golgi apparatus, and then you also have multiple single strands of DNA versus circular DNA. Other things is that eukaryotes tend to be larger, while prokaryotes tend to be smaller, they tend to be simpler. So now that we know the key distinctions, what are examples of eukaryotes? Well, eukaryotes include most of what we interact with on a daily basis or we think we're interacting with on a daily basis. These includes all multicellular organisms, so multicellular, multicellular organisms. So I'm thinking animals, plants, fungi. It includes protists. This is a paramuseum right over here. This is eukaryotic. It's going to have a membrane-bound nucleus and other organelles. This right over here, these are onion root tip cells. So these are plant cells. And you could actually see it's been stained You can actually see the membrane-bound nucleus here. And this is actually a cool picture because you can see the cells at different stages of mitosis, which is interesting. Animal cells, the things that make you you, you are eukaryotic. So what is prokaryotic? Well, bacteria is probably the most common example of that. Bacteria, right over here, these are prokaryotes. And the lesser talk or things that's talked about lot less is archaea. And archaea, people initially thought that these were a form of bacteria that just lived in vary extreme conditions. But now they know it's a completely different domain of life, archaea. And so when we think about the domains of life, the current thought is that you have bacteria here, bacteria here, you have archaea. You have archaea, And then you have, and then you have eukaryotes. I'll do it there, and then you have eukaryotes. And these are things that have all of the traits that we've talked about and so this include plants and animals and fungi and unicellular eukaryotes, protists, and things like that. And so, if we once again, just high level we would consider these prokaryotes and these of course are the eukaryotes. So hopefully that gives you a good overview of things.