Cell : Definition, Structure and its parts Etc.

In this article, we will discuss the cell in a simple and intuitive way and try to understand its many important aspects through necessary pictures.

There is DNA in the cell itself , so understanding of the cell becomes essential to understand DNA. That’s why you must read this article till the end.

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What are cells called?

Cells are the basic building blocks of all living things. The human body is made up of trillions of cells. They provide structure for the body, take in nutrients from food, convert those nutrients into energy, and perform specialized functions. Cells also contain the body’s hereditary material (what we call DNA) and can make copies of themselves.

Cell, meaning cell, is derived from the Latin word ‘cellula’, which means “small room”. The cell is the basic structural and functional unit of life. Each cell consists of a cytoplasm enclosed within a membrane, which contains many biomolecules such as proteins and nucleic acids.

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. Plants and animals are multicellular organisms.

Since unicellular organisms are very micro, hence it is also called micro-organism. On the other hand, talking about plants and animals, there is a wealth of cells in it. You can get an idea of how many cells are there in all of these, from the fact that there are about 40 trillion cells in the human body.

| Cell Types

There are two types of cells: eukaryotic cells and prokaryotic cells . Let us understand both in a little detail;

Prokaryotic cells –Under this, those cells are kept which do not have a nucleus. And generally it is a unicellular organism, it includes 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. [ View Image ]

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.

The main distinguishing feature of eukaryotes compared to prokaryotes is compartmentalization : that is, all closed parts within the cell that are usually surrounded by a single or double lipid layer membrane *. It is called an organelle . It consists of specific activities. And everyone has a job. The most important of these is the cell nucleus, which contains DNA.

Know in detail – Difference between prokaryotic and eukaryotic cells [illustrated]

| Cell Parts

Cells have many parts, each of which has a different function. Some of these parts are called organelles (which we just understood above). These are specialized structures that perform certain functions within the cell. Human cells have the following major parts:

Cytoplasm – Within cells, the cytoplasm is composed of a jelly-like fluid (called the cytosol) and other structures that surround the nucleus. The cytoplasm is about 80% water and is usually colorless.

Most of the cellular activities take place within the cytoplasm, as do many metabolic pathways including glycolysis and processes such as cell division . The concentrated inner region is called the endoplasm and the outer layer is called the cell cortex or ectoplasm.

Cytoskeleton – The cytoskeleton is a network of long filaments that make up the structural framework of the cell. The cytoskeleton is a complex, dynamic network of interconnecting protein filaments present in the cytoplasm of all cells (except for bacteria and archaea). It extends from the nucleus of the cell to the cell membrane and is composed of similar proteins in different organisms.

In eukaryotes, it is composed of three main components, microfilaments, intermediate filaments and microtubules , and all of which are capable of rapid growth or are dependent on the requirements of the cell.

The cytoskeleton has many important functions, including determining cell shape, participating in cell division, and allowing cells to move. It also provides a track-like system that guides the movement of organelles and other substances within cells.

Endoplasmic Reticulum (ER) –This organelle helps process molecules made by the cell. The endoplasmic reticulum also serves to transport these molecules to their specific destinations inside or outside the cell. It is divided into two parts (1) Rough endoplasmic reticulum and (2) Smooth endoplasmic reticulum.

1. Rough endoplasmic reticulum ; The surface of the granular endoplasmic reticulum) is lined with protein-making ribosomes, which gives it a “rough” appearance (hence the name).

2. Smooth endoplasmic reticulum synthesizes lipids, phospholipids and steroids. Cells that secrete these products, such as testis, ovaries, and sebaceous glands, have an abundance of smooth endoplasmic reticulum.

Also read – 15+ DNA Facts that everybody should know

Golgi apparatus –The Golgi apparatus, also known as the Golgi complex, Golgi body, or simply Golgi, is an organelle found in most eukaryotic cells.

It is the endomembrane system in the cytoplasm, and vesicles Packages proteins inside the cell into membrane-bound vesicles before being sent to their destination.

In other words, it packages the processed molecules by the endoplasmic reticulum to be carried out of the cell. [vesicles is discussed further.]

Note –Remember the endomembrane system* is nothing but what separates the cell into different compartments, or organelles, such as the nucleus, the endoplasmic reticulum (ER), the Golgi apparatus, and the lysosome.

Lysosomes – These organelles are the recycling centers of the cell. These are spherical vesicles that contain hydrolytic enzymes*, which can break down a wide variety of biomolecules.

They digest foreign bacteria that have invaded the cell, rid the cell of toxins, and recycle damaged cell components.

You can see in the picture how Lysosomes look inside the cell.

Remember here that hydrolytic enzymes* cleave different groups of biomolecules, such as esters, peptides, and glycosides. Basically, enzymes are proteins that help speed up chemical reactions in our bodies. They build up some substances and break down others. All living things have enzymes. Our body naturally produces enzymes.

Mitochondria – Mitochondria are complex organelles that convert energy from food into a form that the cell can use. This is called Adenosine Triphosphate (or ATP).

They have their own genetic material, separate from the DNA in the nucleus, and can make copies of themselves. The mitochondrion is popularly called the “powerhouse of the cell”.

You can see in this picture how mitochondria, looks like a capsule in the cell.

Nucleus –The nucleus is a membrane-bound organelle found in eukaryotic cells. The nucleus serves as the cell’s command center, sending instructions to the cell to grow, mature, divide, or die.

It also contains DNA (deoxyribonucleic acid), the cell’s hereditary material. The nucleus is surrounded by a membrane called the nuclear envelope , which protects the DNA and separates the nucleus from the rest of the cell.

You can see in this picture how the nucleus is in the middle of the cell.

nucleolus – The nucleolus is the largest structure in the nucleus of eukaryotic cells. It means to say that it is located inside the nucleus. It is known as the site of ribosome biogenesis. Remember here that ribosome biogenesis is the process of making ribosomes.

These nucleoli also participate in the formation of signal recognition particles, and play a role in the cell’s response to stress. Indeed, nucleoli are composed of proteins, DNA, and RNA and are formed around specific chromosomal regions called nuclear organizing regions.

Malfunction of the nucleoli may be the cause of a number of human conditions called “nucleolopathies”, and the nucleolus is being investigated as a target for cancer chemotherapy. [You can see it in the picture below.]

Plasma membrane – The plasma membrane, (also known as the cell membrane or cytoplasmic membrane) is a biological membrane that separates the interior of all cells from the external environment (the extracellular space) and protects the cell.

The cell membrane consists of a lipid bilayer, composed of two layers of phospholipids, containing cholesterol (a lipid component), which maintains appropriate membrane fluidity at different temperatures. Overall it separates the cell from its environment and allows materials to enter and leave the cell.

Ribosomes – Ribosomes are organelles that process the cell’s genetic instructions to make proteins. These organelles may float freely in the cytoplasm or may be attached to the endoplasmic reticulum.

Ribosomes are macromolecular machines, found within all cells, that carry out biological protein synthesis. Ribosomes link together amino acids in the order specified by the codons of messenger RNA (mRNA) molecules to form polypeptide chains*.

The ribosome consists of two major components: the small and large ribosomal subunits. Each subunit consists of one or more ribosomal RNA (rRNA) molecules and several ribosomal proteins (R-proteins).

Note* – Remember here that a polypeptide chain consists of amino acids, which are linked together to form the building blocks of proteins.

vesicle – A vesicle is a structure inside or outside a cell, consisting of a fluid or cytoplasm enclosed by a lipid bilayer.

Vesicles perform a variety of functions. Since it is isolated from the cytosol*, the interior of the vesicle can be isolated from the cytosolic environment. For this reason, vesicles are a basic device used by the cell to organize extracellular materials.

Vesicles are involved in metabolism, transport, buoyancy control, and temporary storage of food and enzymes. They can also act as chemical reaction chambers.

Note – Cytosol* is actually nothing but, in eukaryotic cell, surrounded by cell membrane and is part of cytoplasm, which also includes mitochondria, plastids and other organelles.

vacuole – A vacuole is a membrane-bound organelle present in plant and fungal cells and some protist, animal, and bacterial cells. Vacuoles are essentially enclosed compartments, filled with water containing inorganic and organic molecules including enzymes in solution, although in some cases they may contain solids.

Vacuoles are formed by the fusion of several membrane vesicles. This organelle has no basic shape or size; Its composition varies according to the needs of the cell.

Overall, in this big picture, you can easily see all the parts that where its components are present in a cell.

Facts Related to Cell

Q. What is cell division?

In cell division, a single cell (called a mother cell) is divided into two daughter cells. It leads to multicellular organisms (tissue growth) and reproduction (vegetative reproduction) in unicellular organisms.

Prokaryotic cells divide by binary fission, while eukaryotic cells typically undergo a process of nuclear division, called mitosis, followed by cell division, called cytokinesis.

Read more – Cell Division – What, When and How? [Facts]

Q. When does DNA replication happen?

DNA replication, or the process of copying a cell’s genome, always occurs when a cell divides through mitosis or binary fission.

Q. What is Protein Synthesis?

Cells are able to synthesize new proteins, which are essential for the modulation and maintenance of cellular activities. This process involves the creation of new protein molecules from amino acid building blocks based on the information encoded in DNA/RNA.

Q. What is cell metabolism?

Cell metabolism is the process by which individual cells process nutrient molecules. There are two distinct divisions in metabolism: catabolism, in which the cell breaks down complex molecules to generate energy and reduce energy, and anabolism, in which the cell breaks down complex molecules to build and perform other biological functions. Reduces energy and power to do

Q. What is called mitosis?

Eukaryotic cells usually undergo a process called nuclear division, called mitosis, followed by cell division, called cytokinesis.

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