All living things are categorized into one of two cell types: prokaryotes and eukaryotes.
All living things are categorized into one of two cell types: prokaryotes and eukaryotes. Melanie begins Episode 50 with a nerdy word dive (1:13) before distinguishing between prokaryotic and eukaryotic cells (2:04). Settle in for endosymbiosis story time!(5:02) The episode wraps up with unit connections and exam expectations (6:42).
The Question of the Day asks (7:58) The liver has many functions, one of which is to process alcohol and detoxify the blood. Which organelle would you expect to find in greater quantity within liver cells?
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Hi and welcome to the APsolute Recap: Biology Edition. This is our 50th Episode! Today’s episode will recap Prokaryotic vs. Eukaryotic Cells.
Zoom out:
Unit 2 - Cell Structure and Function
Topic 2.11 - Origins of Cell compartmentalization
Big idea - Evolution
The cell is the most basic unit of life, which for some multicellular organisms become highly specialized and combine to form tissues, organs, and organ systems. But, you don’t need to be that complex. A single cell can survive on its own if it has all the tools to do so. It's typically not a complicated life, and is often a short one. This episode will recap the commonalities and differences between cell types.
Let’s Zoom in:
Nerding out in etymology for a second (which is the study of words and their origins). Eukaryote from the Greek. Eu meaning well, good or true - and karyon meaning nut or kernel. So a eukaryote is described as a good nut? Well not quite. It implies that it has a true kernel, which in our analogy will be the enclosed genetic information in the nucleus. Whereas prokaryote - pro, meaning before - is going to be a cell that lacks a nucleus because it was “before the nut.” Ending in -ote is in noun form, but we can also use these terms as adjectives to describe a type of cell - prokaryotic and eukaryotic. We will see the root word “karyo” in other applications related to DNA, like with a karyotype, the mapping out of chromosomes.
Let’s start with differences first: The main distinguishing features between cell types will be with the nuclear membrane, organelle types, cell size, and genetic organization.
Prokaryotic cells were the first to evolve in the history of life on Earth. They were the only ones around for billions of years! These cells include the Domain Bacteria and Domain Archaea. There is no domain called Prokarya! Sorry. That would be convenient. Prokaryotic cells will not contain a nucleus nor will they have membrane bound organelles. Which means no mitochondria, chloroplasts, endoplasmic reticulum, or Golgi! You may see additional structures like cilia and flagella used for movement and cell walls. They are small and have short life spans. In fact, some bacteria reproduce through binary fission every 30 minutes!
In contrast, Eukaryotic cells are larger and evolved later (some 2.7 bya). These cell types are found in the domain Eukarya with kingdoms Protista, Fungi, Plantae and Animalia. Most protists are unicellular, but - fungi, plants and animals will have eukaryotic cells combining in multicellular organisms. Be careful! Eukaryotes aren’t synonymous with multicellular and prokaryotes don’t mean unicellular, although all prokaryotes are unicellular. Both of the cell types on our podcast cover art are unicellular eukaryotes from the kingdom protista - the amoeba and paramecium! Eukaryotic cells all contain a nucleus and have membrane bound organelles with specialized functions - like the mitochondria, chloroplasts, endoplasmic reticulum, and Golgi! The nucleus stores DNA in multiple strands of linear form (chromatin and the condensed chromosomes) and has a dense nucleolus where rRNA is produced. Some eukaryotic cells will have cell walls, with unique chemical composition per kingdom.
Let’s settle in for a story: Once upon a time, small prokaryotic microbes were minding their own business when a unicellular eukaryote came over and tried to engulf them through phagocytosis. Now instead of digesting the little microbes, they formed a symbiotic relationship. You scratch my back and I’ll scratch yours. The microbes were protected from other external predators and the eukaryote now had an intracellular energy converting factory. Not a bad partnership.
This is known as the endosymbiosis theory. It is thought that both chloroplasts and mitochondria were once independent prokaryotes. Not only do they have their own circular DNA, ribosomes, and replicate independently by binary fission – but they are also approximately the size of existing prokaryotic cells. Furthermore - they have double membranes - the inner membrane representative of their original cell and the outer membrane deriving from the eukaryote that tried to consume them during endocytosis vesicle formation. It’s all compatible since membranes are composed of the same phospholipids and proteins. Fun fact - both mitochondrial and chloroplast DNA follow maternal lineages through sexual reproduction - as eggs and ovules contribute these organelle structures to the embryo. So if you are looking at a plant cell - you find DNA in three separate places: in the nucleus, the mitochondria, and chloroplast.
So what do these cells have in common? Both prokaryotic and eukaryotic cells contain genetic information, cytoplasm, ribosomes and have a plasma membrane. After all, ya gotta make them proteins! They do all the work.
Time for unit connections. You’ll find these cell types in Unit 2 with membrane permeability and structure, Unit 3 with photosynthesis, cellular respiration and the electron transport chain, Unit 4 with signal transduction and the cell cycle, Unit 5 with genetic diversity, Unit 6 with the structure of genetic information, central dogma, and gene expression, and Unit 7 with common ancestry. Alright - what about the exam? You may be asked to compare these cell types, especially with evolution and advantage from one to the other. You will need to distinguish between each strategy for gene expression and they love a good application question related to the endosymbiosis theory. Don’t get stuck on one particular diagram of cell types - focus on application and relative location of organelles as part of processes.
To recap……
Prokaryotes are smaller, do not contain a nucleus nor membrane bound organelles and organize their DNA in a circular loop. Eukaryotes are larger, contain a nucleus and membrane bound organelles and organize their DNA linearly in chromosomes. Both cell types have ribosomes, DNA, cytoplasm and a plasma membrane.
Coming up next on the Apsolute RecAP Biology Edition: Dull King Phillip
Today’s question of the day is about organelles
Question of the day: The liver has many functions, one of which is to process alcohol and detoxify the blood. Which organelle would you expect to find in greater quantity within liver cells?