The year 1665: India’s Taj Mahal was completed 12 years ago; Newton will be inspired to see apples falling from a tree just over a year later ; and somewhere in London, architect and natural philosopher Robert Hooke will The thin wood slice was placed in the specimen holder of the microscope, and he observed a strange structure through the microscope.
“I observed very distinctly that this object was covered with pores throughout, like a honeycomb, but with irregularly shaped pores,” he wrote. “These pores, or cells… are really the first microscopic pores I’ve ever seen, and probably the first microscopic pores ever seen by man, because I’ve never seen any mention of them before. contributors or persons.”
Hooke discovered cells, plant cells to be exact. He actually coined the term, and he records that they resemble the dwellings of the Christian monks in a monastery he once visited. But the cells were dead, and his microscope wasn’t precise enough to see inside the cells. It wasn’t until 13 years later that anyone saw living cells up close.
Dutch businessman and scientist Antonie van Leeuwenhoek used a more sophisticated microscope of his own design to observe bacteria and protozoa for the first time. He called these single-celled organisms microzoans , Latin for “little animals.”
Hooke has long since died and is buried somewhere in the City of London Cemetery. He took the first steps towards what we now know as cell theory. Theoretically, every living organism on Earth consists of one or more cells.
Cells are the key units of structure and function in all living organisms. Every cell that has ever existed has been divided over and over again from cells that have ever existed, up to the 37.2 trillion cells that make up your body.
two different cell types
Cells are mainly divided into two types – prokaryotic cells and eukaryotic cells.
Prokaryotic cells do not have a nucleus. The “little animals” that Leeuwenhoek observed were prokaryotic cells. Bacteria and another group of cell families called archaea are classified as prokaryotes.
Cells present in plants and animals are called eukaryotic cells. This type of cell can be unicellular or multicellular.
But what are eukaryotic cells made of? Suppose you were to shrink down to the size of a eukaryotic cell, or even smaller, what would you see?
Imagine yourself getting smaller and the world around you getting bigger and eventually becoming a blur. As you zoom out, you start to focus on a set of structures, like the lattice that Hooke observed long ago.
Soon, you are in a certain cell. Now, some cells are more complex on the outside, and have appendages that other cells lack. Microvilli are one such feature.
Microvilli extend outward like fingers on the cell surface and are important for nutrient absorption. They also greatly expand the cell’s surface area without compromising its volume. Cilia extend even further than microvilli and can also push different substances along the cell surface.
Then there’s the flagella, which is a thin, tail-like structure that propels the entire cell, allowing the cell to swim!
All cells depend on the all-important cell membrane. It acts like a fence, allowing food and nutrients to enter while maintaining the contents of the cells .
Cell membranes are made of double layers of fatty acids called phospholipids. These fatty acid molecules are divided into a head and a tail. The head structure is called “hydrophilic structure”, which means it can be attracted by water. The tail structure is called “hydrophobic structure”, which means it can be repelled by water. This combination of head and tail is responsible for the structure and function of the cell membrane.
As you get smaller, you pass through cell membranes and start exploring cells. In simple terms, you can see that the bilayer structure of phospholipids is like a zipper, firmly held in place by the chemical attraction of the hydrophobic structure of its tail.
cytoplasm and cytoskeleton
Once you’ve gotten all the way inside the cell, you’ll see a medium called the cytoplasm. The cytoplasm contains a substance rich in amino acids and potassium called the cytosol. This liquid substance is also known as intracellular fluid.
You’ll also find a network that looks like a net or shelf, which is the cytoskeleton. It provides structural support to cells and allows substances to move within cells. The cytoskeleton is composed of three different types of protein fibers, which are microfilaments, intermediate fibers, and microtubules.
Microfilaments, the smallest protein fibers of the three, are composed of twisted strands of protein that can compress together to shorten the cell’s diameter. This compression often occurs in muscle cells to assist in muscle contraction.
Intermediate fibers provide the cellular framework and assist in the integration of twisted strands of proteins.
Microtubules are helical. When microtubules come together, they form a hollow cylinder. These cylinders help maintain cell shape and move organelles (another name for cellular building blocks) within the cell.
The substances they form are called centrosomes. Centrosomes are made up of structures called centrioles, which organize microtubules and provide the cell with extra structure, and they also assist in cell division during cell division.
Between the cytoplasm and the cytoskeleton, you can see the main supporting framework of the cell. You’ll also see some really weird structures, which are organelles. These important cellular components all have their specific functions.
The first structure you can see that looks a lot like a series of elongated cavities is the endoplasmic reticulum (ER). The endoplasmic reticulum is divided into two different types.
One type is the rough endoplasmic reticulum, which extends from the nucleus and has ribosomes attached to the outside of its membrane, giving it a rougher appearance. These ribosomes make something called a polypeptide chain, but that’s just a fancy name for a protein . Proteins produced by ribosomes are released into the ER, where they are processed and prepared for release into the cell. Upon release, ribosomes are transported into closed vesicles and shed from the rough endoplasmic reticulum, which is known as vesicular transport.
It’s worth noting that ribosomes are not organelles, but they are vital to cells. This is because they are where proteins are produced. They can float in the cytoplasm to reach other locations in the cell, or they can attach to the rough endoplasmic reticulum. Ribosomes are composed of two parts, the small subunit and the large subunit. The small subunit is responsible for reading ribonucleic acid (RNA), which contains instructions for assembling amino acids into polypeptide chains. The large subunit does the heavy lifting of actually assembling the polypeptide chain.
Another type is the smooth endoplasmic reticulum, which is another organelle with a membrane. But because it lacks ribosomes on the outside, it has earned the nickname “glossy”. The smooth endoplasmic reticulum contains enzymes that modify peptides, generate lipids and carbohydrates, and destroy toxins. Most of the lipids and carbohydrates that make up cell membranes are produced in the smooth endoplasmic reticulum.
Now you need to turn your attention to the Golgi apparatus, which definitely has the coolest name of any organelle. The Golgi apparatus is another organelle that modifies, packages and stores proteins.
It looks like a set of containers expanding outward from the center, getting bigger and bigger. Vesicular transport transports proteins from the ER to the Golgi apparatus. As proteins pass between containers in the Golgi apparatus, they are modified. Modifications can be made by adding or rearranging molecules with different enzymes, and sometimes by adding carbohydrates to make glycoproteins.
After passing through the final vessel, the protein is sequestered in another vesicle, a different vesicle called the secretory vesicle. The transport direction of most of these proteins is the cell membrane. They either become part of the cell membrane or are released outside the cell.
The Golgi apparatus is the basis for lysosome production. These vesicles shed from the Golgi organ and take over the cell’s garbage transport duties. Lysosomes are enclosed in a thin membrane that contains digestive enzymes that absorb cellular waste or recycle or convert defective organelles into waste. They are also crucial for protecting cells from attack by bacteria and viruses.
After going through the Golgi, you see the proteasome. These organelles manage the proteins already in the cell. They are distributed throughout the cytoplasm. The proteasome breaks down abnormal or misfolded proteins, as well as normal proteins that the cell no longer needs.
In the cytoplasm another protein called ubiquitin is placed on proteins marked by enzymes for recycling. The tagged proteins are then drawn into the proteasome and broken down by a process called proteolysis. During this process, the protein’s peptide bonds are broken, and the remaining peptide chains and amino acids are released into the cell for recycling .
On the rest of your journey, you’ll come across a bizarre structure called a peroxisome. Strictly speaking, it is not
Organelles are not enzymes either, but the word that best describes peroxisomes is protein complex.
They have membranes and also come out of the ER. Peroxisomes are responsible for breaking down long-chain fatty acids and amino acids. In the process, they produce a by-product, hydrogen peroxide, which is dangerous to cells because it reacts with many substances. Because of this, peroxisomes also carry enzymes that convert hydrogen peroxide into water and oxygen, sort of like cleaning up their own garbage.
After passing through the peroxisomes, you’ll see a bean-shaped organelle called the mitochondria (collectively known as mitochondria). They are the ultra-high-energy power plants of the cell. They convert food particles entering the cell into a molecule called adenosine triphosphate, or ATP, which is the “energy flow” in the cell. ATP stores energy and transfers it to other parts of the cell .
Mitochondria have inner and outer membranes, and their numbers vary by cell type. In general, more active cells have more mitochondria. For example, liver cells contain thousands of mitochondria. In fact, aerobic exercise can increase the number of mitochondria in the cells that make up muscle. No wonder you have more energy if you exercise regularly.
Finally, you reach the nucleus. The nucleus is the largest structure in the cell, and its two membranes form the nuclear envelope.
The nuclear envelope, together with the pores on the surface of the membrane, wraps the nucleoplasm. While the nuclear envelope acts as a barrier, pores can open to allow certain molecules to pass in and out of the nucleus. The nucleoplasm is very similar to the cytoplasm, a plasma that separates the structures contained within the nuclear envelope.
Separated within the nuclear envelope is the nucleolus, which is composed of deoxyribonucleic acid (DNA), RNA, and proteins. The nucleolus is where ribosomes are made, and the proteins that ribosomes make, as mentioned above, are critical to healthy cell function.
As you get smaller, you start to notice the twisted double helix structure of your cells’ DNA . You want to reach out and touch it, and as you get smaller and closer to it, you finally reach it. For a split second, you’re back to your original volume, not sure if you’ve actually touched what you wanted to.
Somewhere in a green lawn in the City of London Cemetery, the first ray of sunlight of a new day falls on the young grass that is just sprouting. The grass seed’s cells, nourished by the rich soil and sunlight, divide and thrive in the cool morning air.