Eukaryotic cells: These include a nucleus that is enclosed inside the nuclear membrane. Plants, fungi and protozoa are some of the examples that have eukaryotic cells. Cells are generally classified into two types which are eukaryotic cells and prokaryotic cells. Eukaryotic cells are considered to be more advanced cells and are found in higher organisms.

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Eukaryotic Cell Definition

Eukaryotic cell refers to the cell whose genetic material is surrounded by the nuclear membrane, i.e. has a well-defined nucleus and other membrane-bound organelles. “Eu” means true and “karyon” means nucleus.

Eukaryotic Cell: Characteristics

All living organisms are made of cells. Higher organisms, i.e. all animal cells, plant cells, fungal cells, and protist cells are made up of eukaryotic cells. It has the following characteristics:-

1. The size of the eukaryotic cell is larger than that of the prokaryotic cell. Its size ranges from \(10-100\) micrometers \(\left( {{\rm{\mu ms}}} \right)\) in diameter.
2. A eukaryotic cell is an advanced type of cell that has a well-defined nucleus and multiple membrane-bound organelles.
3. DNA is the genetic material of the eukaryotic cell.
4. The nucleus is surrounded by a complex nuclear membrane.
5. Eukaryotic cells have mitochondria for cellular respiration.
6. The cell wall is present in some of the eukaryotic cells like plant cells and is made of cellulose.
7. Sexual reproduction is seen in almost all of the eukaryotes but in some single-celled eukaryotes like yeast cells, reproduces asexually via mitosis or fission.

Eukaryotic Cell Structure

The list of aspects associated with eukaryotic cell structure are mentioned as follows:

1. The eukaryotic cell is surrounded by a plasma membrane which is made of protein and phospho-lipids.
2. Some of the eukaryotic cells are surrounded by a cell wall like in fungal cells, some protists, and in plant cells. Cell walls give strength and rigidity to the cell.
3. The Nucleus is centrally placed which is a double membranous structure. Nuclear pores are present in the nuclear membrane.
   a. The nucleolus is present in the nucleus.
   b. Innerside of the nucleus is filled with a fluid or matrix called nucleoplasm. This contains chromatin fibre which supercoils to form chromosomes.
4. The Cytoplasm is the fluid present between the plasma membrane and nucleus. This space includes all organelles and other molecules and ions.
5. Endoplasmic Reticulum is a network of tubes that grows from the nuclear membrane. It is a double membranous structure. It can be
   a. Rough endoplasmic reticulum (RER) or
   b. Smooth endoplasmic reticulum (SER)
6. RER is rough due to the presence of ribosomes on its surface and SER is smooth as it has no ribosomes on its surface.
7. Ribosomes are made of rRNA and ribosomal proteins. Ribosomes help in formation of proteins.
8. In eukaryotes, ribosomes are of the \({\rm{’80S’}}\) type. One subunit is of \({\rm{’60S’}}\) while the other is of \({\rm{’40S’}}\).
9. Golgi Complex is made of flattened disc-shaped cisternae. It is involved in packaging and exporting proteins to their destination.
10. Centrioles are cylindrical cell organelle, found near the nucleus which is made of microtubules and its function is the formation of spindle fibre.
11. Mitochondria is a double membranous structure. Its inner layer folds to form a cisternae which are to increases the surface area so that more enzymes can be packed in it to increase the ATP synthesis. Singular is the mitochondrion.
12. Plastid is also a double membranous structure that is present in some eukaryotic cells like plants and algae. It gives green colour to the cell and helps in photosynthesis.

13. Lysosomes are the single membranous structure filled with digestive enzymes which helps to digest worn-out cells and foreign bacteria and viruses.
14. Vacuoles are the membrane-bound structure present in the eukaryotic cell. In animal cells, there are numerous small vacuoles while in plant cells large vacuoles are present. Large vacuoles help in maintaining water balance and keep the cell turgid.
15. The Cytoskeletal Structure provides shape, movement, and anchorage to cells. It is made of microtubules, microfilament, and intermediate proteins.
16. Flagella and cilia which are used for locomotion are made of microtubules. Microtubules are made of alpha and beta-tubulin protein. Microfilaments are made of actin and myosin protein which are found in skeletal muscle. Intermediate filaments are made of many keratin proteins and provide stability to cells.

Eukaryotic Cell Cycle

1. The cell cycle is described as a series of events that repeat several times and include DNA synthesis or duplication, cell growth, and cell division.
2. Cell division results in the formation of two or four new daughter cells.
3. In eukaryotes, the cell cycle is more complicated than prokaryotes.

4. The cell cycle in eukaryotes is divided into the following phases:
a. Interphase- This phase includes
i. \({\rm{G1}}\) phase- It is the first phase hence named the first gap \({\rm{G1}}\) phase). In this phase, the cell grows in size. All the organelles duplicate but DNA duplication is not involved here.
ii. \({\rm{G0}}\) phase- Cell may or may not opt for this phase which occurs after the \({\rm{‘M’}}\) phase. In this phase, the cell is metabolically active but does not show a tendency to divide further.
iii. \({\rm{S}}\) phase- It is the synthesis phase. In this phase, DNA duplication occurs. Centrosomes are also duplicated.
iv. \({\rm{G2}}\) phase- This phase allows the cell to grow more. It prepares the cell for the \({\rm{‘M’}}\) phase or actual cell division. Along with the enlargement of cells, it makes more proteins and organelles.
b. M Phase– This phase includes both mitosis and meiosis. \({\rm{‘M’}}\) phase is the dividing phase of the cell cycle.
c. After going through a series of events, the cell first divides the nucleus into two sets, followed by the division of the cytoplasm. Thus giving rise to two identical daughter cells. This is mitosis. This method of reproduction is seen in lower organisms and in our skin cells.
d. If a parent cell divides twice to give rise to four daughter cells, each with half the amount of genetic material compared to the parent cells. This is a meiotic division, useful in the production of gametes.
e. Will both phases, i.e. Interphase and \({\rm{‘M’}}\) phases have the same time duration?
f. The cell takes a lot of time to prepare for the cell division, i.e. interphase requires more time than \({\rm{M}}\)-phase. Interphase requires \(90\%\) of the time of the cell cycle. Only \(10\% \) of it is required by \({\rm{‘M’}}\)-phase.

Eukaryotic Cell Diagram

The Eukaryotic cell diagram is given below:

Eukaryotic Cell Examples

1. Animal cell- Animal cells are generally smaller than plant cells and can be found in various shapes and sizes. It lacks a cell wall.
2. Plant cell- The plant is also a multicellular organism but it has a cell wall (unlike animal cell and is made of cellulose) with other cell components like plastid, larger vacuole. Plastids are involved in storage, photosynthesis. Larger vacuole keeps the cell turgid.
3. Fungal cell- It has a cell wall made of chitin and other cell components are present. Mostly, fungal cells are multicellular except for the yeast cell which is a unicellular eukaryotic cell.
4. Protozoa- These are unicellular eukaryotes. Like Amoeba, Paramoecium.

Summary

Eukaryotic cells have well-defined nuclei with all the membrane-bound organelles. It may or may not have a cell wall. All multicellular organisms are eukaryotic with a few unicellular organisms like yeast cells. Eukaryotic cells are more complex than prokaryotic cells. Plant and animal cells are examples of eukaryotic cells. The eukaryotic cell undergoes mitosis and meiosis to increase its number and form gametes respectively.

Frequently Asked Questions (FAQs) on Eukaryotic Cell

Frequently asked questions related to eukaryotic cells are listed as follows:

Q.1. What is the eukaryotic cell definition & what is its function?
A.1. Eukaryotic cell refers to the cell which has a well-defined nucleus and other membrane-bound organelles. Its functions are membrane production, protein synthesis,  energy production, etc.

Q.2. How is a prokaryotic cell different from a eukaryotic cell?
A.2.

Basis of classification	Prokaryotic cell	Eukaryotic cell
Nucleus	Lacks well-defined nucleus.	Have a well-defined nucleus.
Multicellular or unicellular	Unicellular	Mostly multicellular except a few exceptions.
Examples	Bacterial cell	Animal and plant cells

Q.3. At what stage of the cell cycle are histone proteins synthesized in a eukaryotic cell?
A.3. Histone proteins are synthesized in the \({\rm{S}}\)-phase of the interphase of the cell cycle.

Q.4. What are the \(4\) characteristics of a eukaryotic cell?
A.4. Characteristics of eukaryotic cells-
a. The eukaryotic cell is surrounded by a plasma membrane.
b. In some eukaryotic cells, the cell wall is also present.
c. A well-defined nucleus is the contrasting character of the eukaryotic cell.
d. It has several membrane-bound organelles, like the endoplasmic reticulum, mitochondria, etc.

Q.5. What are \(4\) examples of eukaryotic cells?
A.5. Examples of eukaryotic cells are-
a. Animal cells
b. Plant cells
c. Fungal cells
d. Protists like Amoeba, Paramecium.

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