Eukaryotic Cells

Eukaryotic Cells- Definition, Characteristics, Structure, Examples

Last Updated on August 24, 2020 by Sagar Aryal

Eukaryotic Cells Definition

Eukaryotic cells are the cells that are complex in structure and function as they have a membrane-bound well-defined nucleus and other membrane-bound organelles.

  • The term “eukaryote” is derived from Greek words, “eu” meaning ‘true’ and “karyon’ meaning ‘nucleus.’
  • Eukaryotic cells have a more advanced structural composition when compared to prokaryotes.
  • By virtue of these advancements, eukaryotic cells are capable of performing more complex functions than prokaryotic cells.

Characteristics of Eukaryotic cells

The general characteristics of eukaryotic cells are listed below:

  1. The size of eukaryotic cells is significantly larger than prokaryotic cells as the size ranges from 10-100 µm in diameter.
  2. The shape of eukaryotic cells varies significantly with the type of cell. Some cells are pleiomorphic like Amoeba, whereas some have a defined shape like plant cells. The shape of the cells is highly influenced by environmental factors as well as other functional adaptations.
  3. Eukaryotic cells have a more advanced cellular organization with multiple membrane-bound organelles and well-defined nucleus.
  4. The genetic material of eukaryotic cells is DNA, and it is linear and has multiple origins of replication.
  5. The nucleus of eukaryotic cells is surrounded by a complex nuclear membrane. The chromosomes in the nucleus are complexed with histone protein to form linear chromosomes as opposed to circular chromosomes of prokaryotes.
  6. The cell wall that is present in some eukaryotic cells is made up of cellulose or other carbohydrates.
  7. Some eukaryotic cells like yeast cells reproduce asexually via mitosis or fission, whereas other cells reproduce sexually.
Eukaryotic Cells
Figure: Eukaryotic cells. Image created with biorender.com

Structure (components/ parts) of Eukaryotic cell

Eukaryotic cells are much larger in size when compared with prokaryotic cells, having the volume about 10,000 times higher than prokaryotic cells. Eukaryotic cells are formed of a number of membrane-bound and membrane-less organelles that all perform together to support the cell’s organization and function. The common component/ parts in eukaryotic cells are as follows:

Cell wall

  • The cell wall is present in some eukaryotic cells like some protists, fungal and plant cells.
  • The cell wall in plants and some protists is made up of cellulose microfibrils and a network of glycans embedded in the matrix of pectin polysaccharides.
  • The composition of the cell wall in fungal cells is different as in fungal cells, the cell wall is composed of a different polysaccharide, chitin.
  • The function of the cell wall, however, is similar in eukaryotic cells. The cell wall provides support and shape to the eukaryotic cells.

Cell membrane/ Plasma membrane/ Cytoplasmic membrane

  • The cell membrane in eukaryotic cells is present inside the cell wall.
  • In cells without the cell wall, the cell membrane functions as the outermost covering that separates the internal contents of the cell from the outside environment.
  • The plasma membrane is made up of phospholipid bilayer with integral proteins embedded between the two layers.
  • The composition of the cell membrane is similar in eukaryotes and prokaryotes.

Cytoplasm

  • The cytoplasm of the eukaryotic cell is a fluid-filled space that accommodates all internal cell organelles and other molecules.
  • The cytoplasm consists of a jelly-like cytosol and a water-soluble solution containing minerals, ions and other molecules.
  • The amount of cytoplasm is higher in eukaryotic cells as compared to prokaryotic cells as the cell volume is more abundant in eukaryotic cells.

Nucleus

  • The nucleus is an organelle present in the cytoplasm of a eukaryotic cell.
  • It is more complicated than the prokaryotic nucleus as the nucleus is surrounded by a nuclear membrane having a composition similar to the plasma membrane.
  • The genome of a eukaryotic cell is present inside the nucleus where it remains coupled with various proteins like the histone protein.
  • Inside the nucleus, the DNA molecules are arranged in chromosomes which are linear and more organized.
  • Additionally, the nucleus also houses a nucleolus that is not surrounded by a membrane but has proteins that make up the ribosomes and rRNA.

Ribosomes

  • In eukaryotic cells, the ribosomes are 80S type containing 60S and 40S subunits.
  • The larger subunit is further composed of 5S RNA, 28S RNA, and proteins, whereas the smaller subunit is composed of 18S RNA and 33 proteins.
  • The ribosomes in eukaryotic cells are found either attached to the endoplasmic reticulum or are found free in the cytoplasm.

Mitochondria and Plastids

  • Mitochondria and plastids are membrane-bound organelles found in the cytoplasm of eukaryotic cells.
  • Both mitochondria and plastids have an extrachromosomal DNA that regulates the functions of the organelles.
  • In mitochondria, the outer membrane is made up of phospholipid bilayer, whereas the inner layer is folded into cristae where the major physiological function of the cell takes place.
  • Plastids are found in eukaryotic cells of plants and algae that provide color to the cell. Additionally, plastids also have a green pigment, chlorophyll, which is required for photosynthesis.

Cytoskeletal structures

  • Many eukaryotic cells have cytoplasmic projections like flagella and cilia that are involved in movement, feeding, and sensation of these cells.
  • These structures are mainly composed of tubulin proteins supported by microfilaments and microtubules.
  • Cytoskeletal structures are also present in the cytoplasm that provides shape and support to the cell.

Division of Eukaryotic cells (Reproduction)

Some eukaryotic cells can divide only by asexual means while other eukaryotic cells divide both sexually as well as asexually.

Asexual reproduction

  • Asexual reproduction is common in all eukaryotic cells except for reproductive cells that form the male and female gamete.
  • The most common mode of asexual reproduction is mitosis, where the cell grows double its size and then divided to form two identical daughter cells.
  • Unicellular fungal cells and protists divide by budding where new cells arise on the surface of dividing cells in the form of a chain.
  • Processes like binary fission and multiple fission are also observed in cells of primitive eukaryotes.
  • Some fungi are also known to divide/ reproduce asexually via sporulation.

Sexual reproduction

  • The cells of the reproductive system in plants and animals are divided by the sexual method.
  • In this method, the cell divided meiotically to form four daughter cells, each with half the number of chromosomes to their parent cell.
  • The sexual reproduction in eukaryotic cells is responsible for the variation in different cells.

Eukaryotic cell examples

Plant cells

Structure of Plant cell
Image created with biorender.com
  • Plant cells are examples of eukaryotic cells where there is a thick cell wall made up of cellulose that provides the shape and structure to the cell.
  • Each plant cell has a larger vacuole in the cytoplasm that maintains the turgor pressure of the cell.
  • Additionally, plant cells are unique among eukaryotic cells as they have chloroplasts containing chlorophyll that plays an essential role during the process of photosynthesis.

Know More: Plant cell- definition, labeled diagram, structure, parts, organelles

Animal cells

Animal cell Diagram
Image created with biorender.com
  • Animal cells are another group of eukaryotic cells that do not have a rigid cell wall.
  • The lack of cell wall in animals allows the cells to acquire different shapes and assists the process of phagocytosis and pinocytosis.
  • Animal cells are different from plant cells as they have a smaller vacuole, and they don’t have chloroplasts.
  • Animal cells have additional organelles, centriole, that generates the mitotic apparatus required during cell division.

Know More: Animal Cell- Definition, Structure, Parts, Functions and Diagram

Fungal cells

  • Fungal cells are similar to plant cells in that they also have a rigid cell wall.
  • However, the cell wall is made up of chitin and not cellulose.
  • Some fungi are unicellular like yeasts, which have tiny holes in their cell membrane that allows the cells to exchange cytoplasm and other organelles.

Protists

  • Protists are the unicellular eukaryotes that are primitive when compared to plant or animal cells.
  • Most protists don’t have a cell wall while some might.
  • Many protists are known to have chloroplast containing chlorophyll while others might have other photosynthetic pigments.
  • Protists are known to have cilia and flagella that assist in the movement of the cells.

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