Eukaryotic Cell Definition
“Eukaryotic cells are the cells that contain a membrane bound nucleus and organelles.”
What is a Eukaryotic Cell?
Eukaryotic cells have a nucleus enclosed within the nuclear membrane and form large and complex organisms. Protozoa, fungi, plants, and animals all have eukaryotic cells. They are classified under the kingdom Eukaryota.
They can maintain different environments in a single cell that allows them to carry out various metabolic reactions. This helps them grow many times larger than the prokaryotic cells.
Characteristics of Eukaryotic Cells
The features of eukaryotic cells are as follows:
Eukaryotic cells have the nucleus enclosed within the nuclear membrane.
The cell has mitochondria.
Flagella and cilia are the locomotory organs in a eukaryotic cell.
A cell wall is the outermost layer of the eukaryotic cells.
The cells divide by a process called mitosis.
The eukaryotic cells contain a cytoskeletal structure.
The nucleus contains a single, linear DNA, which carries all the genetic information.
Structure Of Eukaryotic Cell
The eukaryotic cell structure comprises the following:
- The plasma membrane separates the cell from the outside environment.
- It comprises specific embedded proteins, which help in the exchange of substances in and out of the cell.
- A cell wall is a rigid structure present outside the plant cell. It is, however, absent in animal cells.
- It provides shape to the cell and helps in cell-to-cell interaction.
- It is a protective layer that protects the cell from any injury or pathogen attacks.
- It is composed of cellulose, hemicellulose, pectins, proteins, etc.
Also refer: Cell Wall
The cytoskeleton is present inside the cytoplasm, which consists of microfilaments, microtubules, and fibres to provide perfect shape to the cell, anchor the organelles, and stimulate the cell movement.
It is a network of small, tubular structures that divides the cell surface into two parts: luminal and extraluminal.
Endoplasmic Reticulum is of two types:
Rough Endoplasmic Reticulum contains ribosomes.
Smooth Endoplasmic Reticulum that lacks ribosomes and is therefore smooth.
- The nucleoplasm enclosed within the nucleus contains DNA and proteins.
- The nuclear envelop consists of two layers- the outer membrane and the inner membrane. Both the membranes are permeable to ions, molecules, and RNA material.
- Ribosome production also takes place inside the nucleus.
- It is made up of flat disc-shaped structures called cisternae.
- It is absent in red blood cells of humans and sieve cells of plants.
- They are arranged parallel and concentrically near the nucleus.
- It is an important site for the formation of glycoproteins and glycolipids.
Also read: Golgi Apparatus
These are the main site for protein synthesis and are composed of proteins and ribonucleic acids.
- These are also known as “powerhouse of cells” because they produce energy.
- It consists of an outer membrane and an inner membrane. The inner membrane is divided into folds called cristae.
- They help in the regulation of cell metabolism.
They are known as “suicidal bags” because they possess hydrolytic enzymes to digest protein, lipids, carbohydrates, and nucleic acids.
These are double-membraned structures and are found only in plant cells. These are of three types:
Chloroplast that contains chlorophyll and is involved in photosynthesis.
Chromoplast that contains a pigment called carotene that provides the plants yellow, red, or orange colours.
Leucoplasts that are colourless and store oil, fats, carbohydrates, or proteins.
Eukaryotic Cell Diagram
Eukaryotic cell diagram mentioned below depicts different cell organelles present in eukaryotic cells. The nucleus, endoplasmic reticulum, cytoplasm, mitochondria, ribosomes, lysosomes are clearly mentioned in the diagram.
Explore more about Cell organelles
Eukaryotic Cell Cycle
The eukaryotic cells divide during the cell cycle. The cell passes through different stages during the cycle. There are various checkpoints between each stage.
This is known as the resting phase, and the cell does not divide during this stage. The cell cycle starts at this stage. The cells of the liver, kidney, neurons, and stomach all reach this stage and can remain there for longer periods. Many cells do not enter this stage and divide indefinitely throughout their lives.
In this stage, the cells grow and take in nutrients to prepare them for the division. It consists of three
Gap 1 (G1) – Here the cell enlarges. The proteins also increase.
Synthesis (S) – DNA replication takes place in this phase.
Gap 2 (G2) – Ther cells enlarge further to undergo mitotic division.
Mitosis involves the following stages:
On division, each daughter cell is an exact replica of the original cell.
Examples of Eukaryotic Cells
Eukaryotic cells are exclusively found in plants, animals, fungi, protozoa, and other complex organisms. The examples of eukaryotic cells are mentioned below:
The cell wall is made up of cellulose, which provides support to the plant. It has a large vacuole which maintains the turgor pressure. The plant cell contains chloroplast, which aids in the process of photosynthesis.
The cell wall is made of chitin. Some fungi have holes known as septa which allow the organelles and cytoplasm to pass through them.
These do not have cell walls. Instead, they have a cell membrane. That is why animals have varied shapes. They have the ability to perform phagocytosis and pinocytosis.
Protozoans are unicellular organisms. Some protozoa have cilia for locomotion. A thin layer called pellicle provides supports to the cell.
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Frequently Asked Questions
Are eukaryotic cells unicellular or multicellular?
Eukaryotic cells may be unicellular or multicellular. Paramecium, Euglena, Trypanosoma, Dinoflagellates are unicellular eukaryotes. Plants and animals are multicellular eukaryotes.
What is the most important characteristic of eukaryotic cells that distinguishes it from prokaryotic cells?
Eukaryotic cells have a membrane-bound nucleus. On the contrary, prokaryotic cells lack a true nucleus, i.e., they have no nuclear membrane. Unlike eukaryotic cells, the prokaryotic cells do not have mitochondria, chloroplast and endoplasmic reticulum.
Are viruses eukaryotes?
Viruses are neither eukaryotes nor prokaryotes. Since viruses are a link between living and non-living they are not considered in either category.
What are the salient features of a eukaryotic cell?
A eukaryotic cell has the following important features:
- A eukaryotic cell has a nuclear membrane.
- It has mitochondria, golgi bodies, cell wall.
- It also contains locomotory organs such as cilia and flagella.
- The nucleus has a DNA that carries all the genetic information.
How does a eukaryotic cell divide?
A eukaryotic cell divides by the process of mitosis. It undergoes the following stages during cell division:
When did the first eukaryotic cell evolve?
The first eukaryotic cells evolved about 2 billion years ago. This is explained by the endosymbiotic theory that explains the origin of eukaryotic cells by the prokaryotic organisms. Mitochondria and chloroplasts are believed to have evolved from symbiotic bacteria.
What is the evidence for endosymbiotic theory?
The first evidence in support of endosymbiotic theory is that mitochondria and chloroplast have their own DNA and this DNA is similar to the bacterial DNA. The organelles use their DNA to produce several proteins and enzymes to carry out certain activities.