Cell Organelles

What are Cell Organelles?

The basic and fundamental unit of life is a cell. If at the cellular level, we break apart an organism, then the smallest independent component that would be visible, would be the cell. Cells can be defined as the basic unit of life responsible for all life’s processes. 

A cell has the quality to replicate itself and thus known as the building block of life. Inside each cell, fluid is present which is known as cytoplasm which is enclosed by a membrane. In the cytoplasm, there are several biomolecules present like lipids, nucleic acids and proteins. 

The cellular structures present are called the cell organelles that are suspended in the cytoplasm. Cells can be of various shapes and sizes, essentially like blocks of building structures.


Cell Organelles Definition

The cellular components are called cell organelles. These cell organelles have both membrane (layer) and non-membrane(non-film) bound organelles, present inside the cells and are diverse in their designs and capacities. They coordinate and perform efficiently for the better functioning of the cell. A couple of them work by giving shape and backing, while some help with the movement and generation of cells. The various organelles present within the cell and are classified into three categories as per the presence or absence of membrane - 

Organelles Without Membrane: The cell membrane, Ribosomes, and Cytoskeleton are non-membrane-bound cell organelles. They are present both in prokaryotic cells and therefore the eukaryotic cell.

Single Membrane-Bound Organelles:  These are Vacuole, Lysosome, Golgi bodies, Endoplasmic Reticulum present only during a eukaryotic cell.

Twofold film bound or double-membrane organelles: Nucleus, mitochondria and chloroplast are twofold layer bound organelles present only during a eukaryotic cell. 


List of Cell Organelles and their Functions

Plasma Membrane

The cell wall is additionally termed as a cell wall or cytoplasmic membrane which is composed of a lipid bilayer and proteins.

The plasma membrane is found in both plant and animal cells, it functions as a selective membrane that is permeable. This means that it only allows the entry of certain selective materials in and out of the cell according to the requirement. In an animal cell, the cell wall functions by providing shape and protects the inner contents of the cell. 

Cytoplasm

The cytoplasm is present in both plant and animal cells. They are liquid and jelly-like substances filling all the area between the cell wall and nucleus. They are a combination of water, organic and inorganic compounds. The cytoplasm is one of the vital constituents of the cell. you can find all the cell organelles embedded in the cytoplasm. These cell organelles contain enzymes, mainly liable for controlling all metabolic activity happening within the cell and are the location for many of the chemical reactions within a cell.

Nucleus

The nucleus can be defined as a double-membraned organelle found in eukaryotic cells. Structurally the nucleus is round, covered by a nuclear membrane and is dark in colour. It resembles the shape of a cell membrane and forms a wall between the cytoplasm and nucleus. Nucleoli are tiny spherical bodies. But that is not all as you can also find the chromosomes in the nucleus.

Chromosomes are structurally thin and thread-like structures that carry another important structure called a gene. Genes are a hereditary unit in organisms i.e., it helps in the inheritance of traits from one generation (parents) to a different (offspring). The primary function of the nucleus is to watch cellular activities including metabolism and growth by making use of DNA’s genetic information. Nucleoli within the nucleus are liable for the synthesis of protein and RNA.


Endoplasmic Reticulum

The endoplasmic reticulum may be a network of membranous canals crammed with fluid. They are involved in transporting materials throughout the cell and known as the transport system of the cell. 

There are two unique sorts of Endoplasmic Reticulum:

  1. Rough Endoplasmic Reticulum – They're composed of cisternae, tubules, and vesicles, which are found throughout the cell and are involved in protein manufacturing. 

  2. Smooth Endoplasmic Reticulum – They're the storage organelle, related to the assembly of lipids, steroids, and also liable for detoxifying the cell.

Mitochondria 

Mitochondria are the double-membraned organelles that can be found within the cytoplasm of all eukaryotic cells which provides energy by breaking down carbohydrate and sugar molecules, hence they're also mentioned as the “Powerhouse of the cell.”


Plastids

Plastids are double-membrane organelles that are found within the cells of plants and algae. These plastids play an important role in manufacturing food and storing it. Plastids generally consist of pigments that are often used in the process of photosynthesis. These pigments have the functionality of changing the colour of the cell.

Below are a number of the important plastids and their function -

1. Leucoplasts

Leucoplasts can be found in non-photosynthetic tissues of plants which function as the store-house of protein, lipid, and starch.

2. Chloroplasts

Chloroplasts are a stretched organelle encased by phospholipid film. The chloroplast is formed sort of a disc and therefore the stroma is the fluid within the chloroplast that comprises a circular DNA. Every chloroplast contains a green-hued shade called chlorophyll which is utilized while undergoing photosynthesis. The chlorophyll absorbs light energy from the sun then uses it to convert CO2 and water into glucose.

Ribosomes

Ribosomes are known to be macro-molecular machines that are found in almost all living cells for biological protein synthesis. That’s the reason, the ribosomes are also known as the protein factories of the cell. Ribosomal RNA and Ribosomal proteins are the 2 components that together constitute ribosomes. The main function of the ribosomes consists of the protein synthesis in all living cells that ensure the survival of the cell.


Golgi Apparatus

Golgi Apparatus also referred to as Golgi body is an organelle found altogether in eukaryotic cells which are involved in distributing synthesized macromolecules to varied parts of the cell.

Microbodies

Microbodies are membrane-bound, minute, vesicular organelles, found in both plant and animal cells. They contain various enzymes and proteins and may be visualized only under the microscope. 


Cytoskeleton

It is an endless network of filamentous proteinaceous structures that runs throughout the cytoplasm, from the nucleus to the cell wall. It is found altogether in living cells, notably within the eukaryotes. The cytoskeleton network is made out of various kinds of proteins that can partition quickly or dismantle contingent upon the necessity of the cells. The essential capacities incorporate giving the shape and mechanical protection from the cell against deformity, the contractile idea of the fibres helps in motility during cytokinesis.


Cilia and Flagella

Cilia are hair-like projections, small structures, present outside the cell membrane and work like oars to either move the cell or the ECF. Flagella are somewhat larger and are accountable for cell locomotion. The eukaryotic flagellum varies from its prokaryotic partner structurally. The centre of the cilium and flagellum is known as an axoneme, which contains nine sets of steadily organized peripheral microtubules and a bunch of central microtubules running corresponding to the axis. The central tubules are interconnected by a scaffold and embedded by a central sheath. One of the peripheral microtubular pairs is additionally interconnected to the central sheath by a radial spoke. Hence there's a complete set of 9 radial spokes. The cilia and flagella rise out from centriole-like forms known as basal bodies.


Centrosome and Centrioles

The centrosome organelle is composed of two commonly opposite structures known as centrioles. Each centriole consists of 9 equally spaced peripheral fibrils of tubulin protein, and therefore the fibril may be a set of interlinked triplets. The core, a part of the centriole, is understood as a hub and is proteinaceous. The hub connects the peripheral fibrils via radial spoke, which is formed from proteins. The centrioles from the basal bodies of the cilia and flagella produce spindle fibres during cellular division.


Vacuoles

Vacuoles are generally characterized as storage bubbles of unpredictable shapes which are found in cells. They are liquid-filled organelles enclosed by a film. The vacuole stores the food or a spread of nutrients that a cell might need to survive. In addition, it also stores waste products. The byproducts are at last tossed out by vacuoles. Thus, the remainder of the cell is shielded from contamination. The animal and plant cells have different sizes and numbers of vacuoles. Compared to animals, plant cells have larger vacuoles.

FAQs (Frequently Asked Questions)

1. What is a Cell?

Ans - Cell can be defined as the basic unit of life upon which the survival of organisms is dependent.

2. What are the Three Categories of Organelles?

Ans - The three categories of organelles are - organelles without membrane, single-membrane bound organelles and double-membrane bound organelles. 

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