Eukaryotic Cells: Structure, Characteristics, Diagram, Example

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Uncover the secrets of eukaryotic cells – delve into their structure, characteristics, diagrams, and find inspiration in real-life examples.

Eukaryotic Cell Definition

“Eukaryotic cells are the cells that contain a membrane bound nucleus and organelles.”

What is a Eukaryotic Cell?

  • Eukaryotic cells consist of a nucleus enclosed by the nuclear membrane and are integral to the development of large and intricate organisms.
  • In India, various life forms such as Protozoa, fungi, plants, and animals exhibit eukaryotic cellular structures, falling within the kingdom Eukaryota.
  • The adaptability of eukaryotic cells enables them to sustain diverse environments within a singular cell, facilitating the execution of a wide array of metabolic reactions.
  • This adaptability is a key factor that allows eukaryotic cells to achieve sizes significantly larger than those attainable by prokaryotic cells.

Characteristics of Eukaryotic Cells

  • The nucleus in eukaryotic cells is enclosed within the nuclear membrane.
  • Eukaryotic cells feature mitochondria.
  • Locomotion in eukaryotic cells is facilitated by flagella and cilia.
  • The outermost layer of eukaryotic cells is constituted by a cell wall.
  • Cell division in eukaryotic cells occurs through a process known as mitosis.
  • Eukaryotic cells possess a cytoskeletal structure.
  • Within the nucleus of eukaryotic cells, a single, linear DNA carries all genetic information.

Structure Of Eukaryotic Cell

Plasma Membrane

  • Separates the cell from the external environment.
  • Contains embedded proteins facilitating substance exchange in and out of the cell.

Cell Wall

  • Rigid structure located outside plant cells; absent in animal cells.
  • Imparts shape to the cell and facilitates cell-to-cell interaction.
  • Acts as a protective layer, shielding the cell from injuries and pathogen attacks.
  • Composed of cellulose, hemicellulose, pectins, proteins, etc.

Cytoskeleton

  • Located within the cytoplasm, it comprises microfilaments, microtubules, and fibers.
  • Functions include shaping the cell, anchoring organelles, and promoting cell movement.

Endoplasmic Reticulum

  • Network of small, tubular structures.
  • Divides the cell surface into luminal and extraluminal parts.
  • Two types of Endoplasmic Reticulum are present in the cell.
  • Rough Endoplasmic Reticulum: Contains ribosomes.
  • Smooth Endoplasmic Reticulum: Lacks ribosomes, giving it a smooth appearance.

Nucleus

  • The nucleoplasm within the nucleus houses DNA and proteins.
  • The nuclear envelope comprises outer and inner membranes, both permeable to ions, molecules, and RNA material.
  • Ribosome production occurs within the nucleus.

Golgi Apparatus

  • Composed of flat disc-shaped structures called cisternae.
  • Absent in human red blood cells and plant sieve cells.
  • Arranged parallel and concentrically near the nucleus.
  • Vital site for the formation of glycoproteins and glycolipids.

Ribosomes

  • The primary site for protein synthesis is composed of proteins and ribonucleic acids.

Mitochondria

  • Referred to as the “powerhouse of cells” due to energy production.
  • Comprises an outer membrane and an inner membrane with folds known as cristae.
  • Regulates cell metabolism.

Lysosomes

  • Termed “suicidal bags” for their possession of hydrolytic enzymes that digest proteins, lipids, carbohydrates, and nucleic acids.

Plastids

  • Double-membraned structures are found exclusively in plant cells.

Three types of Plastids

  • Chloroplast: Contains chlorophyll, involved in photosynthesis.
  • Chromoplast: Holds pigment like carotene, imparting yellow, red, or orange colors to plants.
  • Leucoplast: Colorless, storing oil, fats, carbohydrates, or proteins.

Eukaryotic Cell Diagram

The diagram of a eukaryotic cell includes the following organelles:

  • Nucleus
  • Endoplasmic Reticulum
  • Cytoplasm
  • Mitochondria
  • Ribosomes
  • Lysosomes

These organelles are distinctly represented in the diagram, providing a visual depiction of the key components of a eukaryotic cell.

Eukaryotic Cell Diagram
Eukaryotic Cell Diagram (Photo: Sciencefacts.net)

Cell Cycle of Eukaryotic Cell

  • Eukaryotic cells undergo division through a process known as the cell cycle.
  • The cell cycle consists of distinct stages, with checkpoints regulating progression between these stages.

Quiescence (G0)

  • Known as the resting phase, where the cell does not undergo division.
  • Marks the beginning of the cell cycle.
  • Some cells, like liver, kidney, neurons, and stomach cells, can enter and stay in this stage for extended periods.
  • Not all cells enter G0; some continuously divide throughout their lifespan.

Interphase

  • Cells grow and absorb nutrients in preparation for division.
  • Three checkpoints:
    • Gap 1 (G1): Cell enlargement and increase in protein content.
    • Synthesis (S): DNA replication occurs.
    • Gap 2 (G2): Further cell enlargement in preparation for mitotic division.

Mitosis

Involves the following stages:

  • Prophase
  • Prometaphase
  • Metaphase
  • Anaphase
  • Telophase
  • Cytokinesis
  • Division of the cell, resulting in two daughter cells.
  • Each daughter cell is a replica of the original cell.

Examples of Eukaryotic Cells

Plant Cells

  • Cell wall made of cellulose, providing structural support.
  • Large vacuole maintaining turgor pressure.
  • Presence of chloroplasts aiding in photosynthesis.

Fungal Cells

  • A cell wall is composed of chitin.
  • Some fungi have septa, allowing organelles and cytoplasm to pass through.

Animal Cells

  • Lack of cell walls possesses a cell membrane.
  • Varied shapes due to the absence of rigid cell walls.
  • Capable of phagocytosis and pinocytosis.

Protozoa

  • Unicellular organisms.
  • Some protozoa use cilia for locomotion.
  • Supported by a thin layer called a pellicle.

Frequently Asked Questions

Q1. Are eukaryotic cells unicellular or multicellular?

Eukaryotic cells may be either unicellular or multicellular. Examples of unicellular eukaryotes include Paramecium, Euglena, Trypanosoma, and Dinoflagellates, while plants and animals represent multicellular eukaryotes.

Q2. What is the most important characteristic of eukaryotic cells that distinguishes it from prokaryotic cells?

The most significant distinction is that eukaryotic cells have a membrane-bound nucleus, whereas prokaryotic cells lack a true nucleus, lacking a nuclear membrane. Additionally, eukaryotic cells possess organelles like mitochondria, chloroplasts, and endoplasmic reticulum, which are absent in prokaryotic cells.

Q3. Are viruses eukaryotes?

Viruses do not fall into the categories of eukaryotes or prokaryotes. Given that viruses exist as a bridge between living and non-living entities, they are not classified within either category.

Q4. What are the salient features of a eukaryotic cell?

Key features of a eukaryotic cell include:

  • Nuclear membrane
  • The presence of mitochondria, Golgi bodies, and cell wall
  • Locomotory organs such as cilia and flagella
  • Nucleus containing DNA carrying genetic information

Q5. How does a eukaryotic cell divide?

Eukaryotic cells divide through the process of mitosis, involving stages like prophase, metaphase, anaphase, telophase, and cytokinesis.

Q6. When did the first eukaryotic cell evolve?

The first eukaryotic cells are estimated to have evolved around 2 billion years ago, according to the endosymbiotic theory, which suggests the origin of eukaryotic cells from prokaryotic organisms.


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