Prokaryotic and Eukaryotic cells [illustrated]

In this article, we will discuss prokaryotic and eukaryotic cells in a simple and intuitive way and illustrate its various important aspects.

There are types of cells prokaryotic and eukaryotic. In order to understand DNA, it is necessary to understand the cell. So read it till the end and like our Facebook page for regular updates .

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| What are cells?

Cell is derived from the Latin word ‘cellula’, which means “small room”. The cell is the basic structural and functional unit of life. It is the smallest unit that can live on its own and which makes up all living organisms and body tissues.

A cell has three main parts: the cell membrane, the nucleus, and the cytoplasm.

The cell membrane surrounds the cell and controls the substances that move in and out of the cell.

The nucleus, or nucleus, is a structure inside the cell that contains the nucleolus and most of the cell’s DNA. It is also where most RNA is made.

The cytoplasm or cytoplasm is the fluid inside the cell. It contains other small cell parts that have specific functions, including the Golgi complex, mitochondria, and the endoplasmic reticulum. The cytoplasm is where most chemical reactions take place and where most proteins are made.

[ Note- All the terms used here such as Golgi complex, mitochondria, etc., all have been discussed further]

Most plant and animal cells are visible only under a light microscope, ranging in size from 1 to 100 micrometers. (1 micrometer i.e. one millionth of a meter).

Such organisms which are composed of only one cell are called unicellular organisms such as bacteria. And such organisms which are made up of many cells are called multicellular organisms, such as plants and animals.

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Cell Types

There are two types of cells: (1) eukaryotic cells and (2) prokaryotic cells.

(1) prokaryotic cells

A cell that does not have a nucleus, called prokaryotic cell. Generally it is a unicellular organism, such cells include bacteria and archaea. Prokaryotic cells were the first form of life on Earth, carrying out important biological processes, including cell signaling.

The DNA of a prokaryotic cell consists of a single circular chromosome, which is in direct contact with the cytoplasm. That is to say, a prokaryotic cell may not have a nucleus, but it does have a nucleoid region, and it contains genetic material. Most prokaryotes are the smallest of all organisms, ranging in diameter from 0.5 to 2.0 µm.

A prokaryotic cell consists of the following regions:

Cell envelope – If you look under it, we see a capsule as the outermost cover. This outermost layer is often made of sugars or special proteins. It helps protect the bacteria from being eaten by larger cells such as animal immune cells and becoming infected with viruses.

Below the capsule, there is a cell wall and a layer of plasma membrane below it.

Most prokaryotes have both a cell membrane and a cell wall, but there are exceptions such as mycoplasma (bacteria) and thermoplasma (archaea) which have only a cell membrane layer.

Overall, the envelope stiffens the cell and acts as a protective filter, separating the cell’s interior from its environment.

Cytoplasm – Inside the cell is the cytoplasmic region that contains the genome (DNA), ribosomes, and a variety of components. But since the nucleus is not found in prokaryotes, the genetic material or DNA is freely found in the cytoplasm. That region is called a nucleoid.

Flagellum and pilus – on the outside, the flagellum (that is, the tail structure) and pilus (ie hair structure) is present. These are structures made of proteins that facilitate movement and communication between cells. However, it is not present in all prokaryotes. Pilus is also known as Fimbriae.

यह भी पढ़ें – DNA and RNA : Differences and Similarities

(2) eukaryotic cells

Under this, those cells are kept, which have a nucleus. It can be unicellular as well as multicellular. Plants, animals, fungi, protozoa and algae are all eukaryotic. These cells are about fifteen times as wide as a typical prokaryote and can be a thousand times more in volume.

Eukaryotic DNA is organized into one or more linear molecules, called chromosomes, which are linked by histone proteins. All chromosomal DNA is stored in the nucleus of the cell, separated from the cytoplasm by a membrane.

The main feature of eukaryotes compared to prokaryotes is its compartmentalization : that is, the enclosed parts within the cell that are usually surrounded by a single or double lipid layer membrane*. It is called an organelle . There are specific activities going on in this and everyone has a job of his own.

A eukaryotic cell consists of the following regions or organelles :

Cytoplasm – It is a term for all the contents of a cell other than the nucleus, the cytoplasm being mostly water.

Endoplasmic Reticulum (ER) – Endoplasmic reticulum, it is a network of membranes throughout the cytoplasm of the cell. It is of two types;

When ribosomes are attached to it, it is called rough endoplasmic reticulum and when ribosomes are not attached to it, it is called smooth endoplasmic reticulum.

The rough endoplasmic reticulum is where most of the protein synthesis in the cell takes place. Whereas the function of smooth endoplasmic reticulum is to synthesize lipids in the cell. Smooth ER also helps in detoxification of harmful substances in the cell.

Golgi apparatus – It is the organelle in the cell that is responsible for sorting and correctly shipping the proteins produced in the endoplasmic reticulum. Like our postal packages, which must have a correct shipping address, proteins produced in the ER must be shipped correctly to their respective address. It is a very important step in protein synthesis. If golgi complex makes a mistake in sending the protein to the correct address, some functions in the cell can stop.

Lysosomes – Produced by the Golgi apparatus, they help break down large molecules into smaller pieces that the cell can use.

Mitochondria – It is the powerhouse of the cell. This organelle packages the energy from the food you eat into ATP (Adenosine triphosphate) molecules.

Each type of cell has a different amount of mitochondria. Cells that have to do a lot of work have more mitochondria, for example- muscle cells in your leg, muscle cells in the heart, etc. Other cells require less energy to do their jobs and have fewer mitochondria.

Nucleus – The nucleus is the control center of the cell. It is the largest organelle of the cell and contains the DNA of the cell.

Nucleolus – Bacteria do not have a nucleus to hold their nuclear DNA. Instead, their DNA is found in the nucleoid. This structure has no protective membrane, but the DNA material is tightly packed and also contains some RNA and proteins.

Plasma membrane – The membrane that surrounds a cell is made up of two lipid layers called “bilipid” membranes. The lipids present in the plasma membrane are called “phospholipids”.

These lipid layers are composed of several fatty acid building blocks. The fatty acids that make up this membrane have two distinct parts—a smaller water-loving head—called the hydrophilic head. Hydro means water and philik means to like or be loved.

The other part of this fatty acid is a long water-repellent or water-hating tail, called the hydrophobic head.

Ribosomes – It is the organelle that helps in the synthesis of proteins. Ribosomes are made up of two parts, called subunits. They get their name from their shape. One unit is larger than the other so they are called major and minor subunits.

Both these subunits are essential for protein synthesis in the cell. When two units are docked with a special information unit, called messenger RNA (mRNA), they form a protein.

Some ribosomes are found in the cytoplasm, but most are associated with the endoplasmic reticulum. While attached to the ER, ribosomes make proteins that the cell needs and that are exported from the cell to function elsewhere in the body.

Vesicle – The word literally means “small vessel”. This organelle helps to store and transport the products produced by the cell.

Vesicles are transport and delivery vehicles like our postal or courier trucks. Some vesicles transport material to certain parts of the cell and others transport material outside the cell in a process called exocytosis.

Vacuole – In plant cells, what looks like a very large empty space in the middle. This space is called a vacuole. The vacuole contains a large amount of water and stores other important materials such as sugars, ions and pigments.

[ Note– All the terms used here such as Golgi complex, mitochondria etc., must read the exact analysis of the cell^link to understand all in detail^]

|difference between prokaryotic and eukaryotic cells

	prokaryotes	eukaryotes
related organisms	bacteria, archaea	protists, fungi , plants , animals
size	1–5 micrometer	10–100 micrometer
Nucleus	It does not have a nucleus, instead it has a nucleoid region.	Happens in it.
Mitochondria	It doesn’t happen in it.	It could be in the thousands.
Chloroplasts	It doesn’t happen in this.	Occurs in plant cell.
organization	Usually unicellular.	It can be unicellular as well as multicellular.
cell division	Prokaryotic cells divide by binary fission.	Eukaryotic cells undergo a process of nuclear division called mitosis.
Chromosomes	There is only one chromosome.	There is more than one chromosome.
Membranes	There is a cell membrane.	Along with the cell membrane, there are also membrane bound organelles.

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Overall, in this article about prokaryotic and eukaryotic cells, I hope you have understood prokaryotic and eukaryotic cells well; Be sure to read other related articles for better understanding.

Cell Division – What, When and How? [Facts]
DNA Sequencing : Meaning, Methods & Applications
DNA Test [Genetic Testing] What, How & Benefits

References,
https://www.cancer.gov/publications/dictionaries/cancer-terms/def/cell
Cell biology – wikipedia
Building Blocks of LIfe