Understanding Cell Structure: The Amazing World Inside a Cell
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Introduction
Have you ever had a moment in your science classes that sparked your curiosity and passion for the subject? For many, this might be dissecting a frog, analyzing an owl pellet, or maybe witnessing the incredible life of an amoeba through a microscope. In this article, we will dive deep into the marvelous world of cell structure. We will explore how cells work, the different types of cells, their organelles, and the modern cell theory that emphasizes their significance in living organisms.
The Modern Cell Theory
The modern cell theory is a cornerstone of biological sciences and consists of three key tenets:
- The Cell is the Smallest Living Unit: All living organisms are composed of cells, which explains that cells are the basic building blocks of life.
- All Living Things are Made of Cells: This aspect underlines that whether unicellular (like an amoeba) or multicellular (like humans), every organism is formed from one or more cells.
- All Cells Come from Other Pre-existing Cells: This principle emphasizes cellular reproduction and how new cells arise from existing ones.
Exploring cells can lead to profound awe regarding the complexities of life. Did you know that every human body consists of billions of cells, all functioning together in harmony? It’s time to delve deeper into the types of cells, starting from the basic structure.
Prokaryotic and Eukaryotic Cells
Cells can be classified into two main categories: prokaryotes and eukaryotes.
Prokaryotic Cells
- Definition: Prokaryotic cells are simple, single-celled organisms without a nucleus.
- Examples: Bacteria and Archaea.
- Characteristics:
- Lack membrane-bound organelles.
- Genetic material is located in a nucleoid region.
- Smaller size compared to eukaryotic cells.
Eukaryotic Cells
- Definition: Eukaryotic cells are more complex and can be unicellular or multicellular.
- Examples: Plants, animals, fungi, and protists.
- Characteristics:
- Have a true nucleus enclosing their genetic material.
- Contain various membrane-bound organelles.
Both prokaryotic and eukaryotic cells share some common structures:
- Genetic Material: DNA is present in both types of cells.
- Cytoplasm: This jelly-like substance fills the cell.
- Ribosomes: Small organelles that synthesize proteins.
- Cell Membrane: This semi-permeable membrane regulates what enters and exits the cell.
Organelles: The Cell’s Interior Machinery
Eukaryotic cells house numerous organelles that specialize in particular functions, making cellular processes efficient and organized. Let's explore some of these vital components:
1. The Nucleus
- Function: Serves as the control center of the cell.
- Characteristics:
- Contains genetic material (DNA).
- House of the nucleolus, where ribosomes are synthesized.
2. Endoplasmic Reticulum (ER)
The endoplasmic reticulum plays a crucial role in synthesizing proteins and lipids.
- Types:
- Rough ER: Studded with ribosomes; involved in protein synthesis and modification.
- Smooth ER: Lacks ribosomes; functions in lipid production and detoxification processes.
3. Golgi Apparatus
- Function: This organelle acts as a packaging and sorting center for molecules synthesized in the ER.
- Process:
- Receives vesicles from the ER.
- Modifies and sorts proteins before sending them to their final destination, be it within or outside the cell.
4. Mitochondria
- Function: Known as the powerhouse of the cell, mitochondria execute cellular respiration to produce ATP energy.
- Description: Structures embedded with their own DNA, allowing them to reproduce independently within the cell.
5. Chloroplasts (in Plant Cells)
- Function: Responsible for photosynthesis, using light energy to produce glucose.
- Characteristic: They contain chlorophyll, which gives plants their green color.
6. Vacuoles
- Function: Storage compartments for various substances such as nutrients, waste products, and cellular metabolism byproducts.
- Type:
- Central Vacuole: Large vacuole found in plant cells, providing structural support and storage.
- Smaller Vacuoles: Common in animal cells, serving various storage functions.
7. Cytoskeleton
- Function: This network of fibers provides structural support, helps maintain the shape of the cell, and plays a role in cell movement.
Getting Out of the Cell
In discussing how various components interact within the cell, it's important to understand how proteins eventually exit. Here’s an example of the protein secretion process:
- A protein is synthesized by a ribosome bound to the Rough ER.
- The protein is transported via vesicles to the Golgi apparatus.
- After processing and modification, a new vesicle forms at the Golgi apparatus.
- Finally, the vesicle carries the protein to the cell membrane and releases it outside the cell.
Conclusion
The world inside a cell is intricate and full of wonders. From the crucial organelles like the nucleus and mitochondria to the structures that maintain cell integrity like the cytoskeleton, every part plays a fundamental role in keeping the cell functional. Whether you are engaging in hands-on experiments in the classroom or gazing at a simple amoeba through a microscope, remember the complexity and beauty of cellular life. The journey of understanding cells does not end here—there’s always more to explore! Stay curious, and keep asking questions about the fascinating world of science!
Captions are on! Click "CC"at bottom right to turn off. Follow us on Twitter (@AmoebaSisters) and Facebook! If you had to think about the most exciting day you ever had in a science classroom, which
day would that be? Looking back through the years---we have a few. The time we participated in an earthworm dissection.
The time we took apart an owl pellet. The osmosis eggs. All of the fruit flies in genetic experiments.
Oh, I could go on, but I will never forget one day in my 9th grade science class. My teacher brought in pond water. And I put one drop of pond water on a microscope slide and saw the most amazing thing ever…I
saw, an amoeba. A single celled amoeba on that microscope slide, and I was forever stuck on science from that point on.
Because I could not believe this little cell was there, alive on this slide, still eating because that’s what amoebas do a lot. To imagine that every person is actually made of billions of cells---of course not amoeba
cells but animals cells--- billions of animal cells, is fascinating. In fact, it really makes you reflect on some of the incredible statements of the modern cell theory.
The modern cell theory includes the following: 1st that the cell is the smallest living unit in all organisms. 2nd that all living things are made of cells.
One or more cells. The amoeba I observed was a single-celled organism, so unicellular. Humans are made of many cells, so multicellular.
And 3rd, all cells come from other, pre-existing cells. Cells have their own little world inside them. They carry genetic information!
They can divide! Many have functions and processes that their organelles, structures inside them, can take care of.
On our planet, we can divide cells into two major groups. As a cell, you’re either a prokaryote or an eukaryote. Bacteria and Arachae are prokaryotes.
Everything else---plants, animals, fungi, protists----are eukaryotes. Both prokaryotes and eukaryotes have genetic material. Both have cytoplasm.
Both have ribosomes, which are small organelles that make proteins. Both have cell membranes which control what goes in and out of the cell. But what makes them different is a big deal.
Prokaryote---pro rhymes with no---they have no nucleus which holds the genetic material and controls the cell’s activities. Prokaryotes have no membrane bound organelles.
Membrane bound organelles are fancy organelles like the nucleus and mitochondria and golgi apparatus. Eukaryotes---eu rhymes with do----they do have membrane bound organelles.
So now you may be wondering what do the organelles do---what are their functions? Well you know our style---we love our science with a side of comics. So we want to take you on a tour of the ride of your life---into the inside of a cell!
To start our trip, we’re first going to have to get through this cell membrane, also called a plasma membrane. It’s selectively permeable which means that it only lets certain select materials in and
out. By doing so, it keeps things in the cell stable---also known as keeping homeostasis. We have an entire video on just the membrane
itself---which is found in all cells, but for now, we’re just going to have to squeeze through this protein in the membrane. Inside the cell, we find ourselves in this jelly like material called cytoplasm.
It surrounds all of these internal cell structures, and you’ll find it inside both prokaryotes and eukaryotes. Now organelles that are just floating around in the cytoplasm can have more support than
you might think. Cells contain a cytoskeleton which is a collection of fibers that will provide support for the cell and its organelles.
The cytoskeleton can even play a major role in movement. The cytoskeleton actually deserves its own video though because it is very complex---and its organization varies depending on what kind of cell you’re looking at.
Moving through this cytoplasm, let’s start with ribosomes. They are NOT membrane bound organelles and they are going to be in both prokaryotes and eukaryotes.
And they make protein. Which is really important because that’s what so much of genetic material---DNA codes for---protein.
Ribosomes can be free in the cytoplasm. They can be attached to another organelle too, which we’ll talk about a bit later. We are now going to focus on eukaryote organelles, which means, organelles that will be membrane
bound. So this takes our travel to the big boss, the nucleus. In eukaryotes, it holds the genetic material.
Genetic material as in DNA for example. All cells have DNA but if you’re an eukaryote, you have a nucleus to put it in. The nucleus controls the cell activities.
Inside it, it has a nucleolus, which is where ribosomes can be produced. Attached to the membrane of the nucleus, or nuclear membrane, you can find the endoplasmic reticulum.
ER for short. It does a lot of processing of molecules for the cell---like protein folding----and it also is highly involved in actually transporting those molecules around.
Like a highway! There is rough ER which has ribosomes attached to it, making it---as you can imagine---rough. And them smooth ER which doesn’t have the ribosomes.
Rough ER specifically tends to be involved with protein producing and transporting, because remember that ribosomes make protein. Molecules that leave the ER can be sent away in vesicles that actually pinch off of the
ER themselves. Smooth ER has many additional roles including detoxification, which is one reason why your liver cells tend to have a lot of smooth ER.
Another additional role of smooth ER is that it can make some types of lipids. Next the Golgi apparatus. It’s the ultimate packaging center.
It can receive items from the transport vesicles that pinched off of the ER. It has enzymes that can modify molecules it may receive and it sorts the materials it receives as well.
It can determine where to send those molecules---including some that may eventually be sent to the membrane so they can be secreted, which means, items that can sent out of the cell. So with all that’s going on in here, you might start to wonder…what’s powering
Like a power plant! This thing makes ATP energy in a process called cellular respiration. It’s not a type of power plant that you would think of…it runs on glucose, which
is a sugar, and needs the presence of oxygen to efficiently make ATP energy. Now at this point, we need to mention that eukaryotes are not a one size fits all. Animal cells can have differences from plant cells. We have a…fork in the road here.
For example, plant cells not only have mitochondria, but they also can have these awesome organelles called chloroplasts. Chloroplasts actually make glucose by using light energy in a process known as photosynthesis.
They tend to have a green look to them because they have a pigment that captures light energy and reflects green light. Both plant and animal cells can have vacuoles---now vacuoles can have a lot of different functions
but many types act as storage of materials. Plant cells can have one large vacuole called a central vacuole while animal cells can have several smaller vacuoles.
Remember how we already said that all cells have membranes? Plant cells additionally have a cell wall which is a layer that offers additional protection and shape maintenance that animal cells do not.
Hmm now how to get out of this animal cell we’ve been in? Well…we could get out like a protein would. So if we were a protein, we would only be made because of instructions from DNA and
remember that in Eukaryotes, DNA is found in the nucleus. We would be made by a ribosome. The ribosomes could be attached to the Rough ER.
The Rough ER highway would provide a vesicle to send us to the Golgi apparatus where the sorting can take place. And…if we’re tagged for being secreted...we’re sent off thru a vesicle from the Golgi to
the membrane. And…out we go! Just keep in mind that in our quick tour, there are still so many more awesome organelles
found in different types of eukaryote cells to continue exploring so to the Google for more! Well that’s it for the Amoeba Sisters and we remind you to stay curious!