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Eukaryotic cells are the ones with an ordered nucleus and organelles encircled by membrane-bound organelles.
- Eukaryotic cells have a number of organelles that perform different activities within the cell.
- "Eukaryotes" are organisms made up of eukaryotic cells, which include plants, animals, fungi, and protists.
- Eukaryotes make up a minuscule fraction of all life. Their total global biomass is estimated roughly equivalent to that of prokaryotes due to their typically considerably bigger size.
Also check: Fundamental Unit of Life
Key terms: Eukaryotic, cells, Eukaryote, Mitochondria, Mitosis, Cytokinesis, Cytoskeleton, Nucleus, Lysosomes, Ribosomes
What is a Eukaryotic Cell?
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Eukaryotes can be single-celled or multicellular in nature. Eukaryotes are distinguished from the prokaryotes group of organisms by the existence of internal membranes that divide some eukaryotic cell components from the remainder of the cytoplasm. These membrane-bound entities are referred to as organelles.
- Eukaryotic cells are those with complicated structures. They contain membrane-like organelles such as the Golgi apparatus, mitochondria, and chloroplasts found in algae and plants.
- Eukaryotes may reproduce both asexually and sexually via mitosis and gamete fusion.
- Mitosis is the process through which one cell splits into two genetically identical cells. There are two rounds of cell division in DNA replication. It is to create four haploid daughter cells in meiosis. They function as sex cells or gametes.
- Each gamete contains just one set of chromosomes that are a unique mixture of the matching pair of parental chromosomes, a consequence of genetic recombination during meiosis.
Also check: Prokaryotic and Eukaryotic Cells
Characteristics of Eukaryotic cell
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Eukaryotic cells have a more complex cellular structure that includes numerous membrane-bound organelles and a well-defined nucleus.It has the following characteristics.
- Eukaryotic cells are much bigger, with diameters ranging from 10-100 meters.
- The cytoskeletal structure is there in eukaryotic cells.
- Mitochondria are in eukaryotic cells.
- A complex nuclear membrane surrounds the nucleus of eukaryotic cells.
- DNA is the genetic substance of eukaryotic cells; it is linear and has numerous replication sources.
- Some eukaryotic cells have a cell wall composed of cellulose or other carbohydrates.
- Chromosomes in the nucleus are complexed with histone protein to create linear chromosomes.
- Some eukaryotic cells, such as yeast cells, reproduce asexually by mitosis or fission, whereas others reproduce sexually.
- The form of eukaryotic cells varies greatly depending on the kind of cell. Some cells, like Amoeba, are pleiomorphic, but others, like plant cells, have a distinct form. Environmental variables, as well as other functional adaptations, have an impact on cell shape.
Also check: Characteristics Of Organisms
Structure of Eukaryotic Cell
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The eukaryotic cell structure includes the following eukaryotic cell parts:
Eukaryotic cell Diagram
Plasma Membrane
The plasma membrane, also known as the cell membrane, is a thin sheet found in all cells. It is needed for separating the interior of the cell from its exterior.
Structure of Plasma membrane
- It shields the cells from trauma and shock.
- Proteins, carbohydrates, and two layers of phospholipids make up the plasma membrane of eukaryotic cells.
- It has specially inserted proteins that aid in the flow of chemicals within and outside the cell.
Cell Wall
A cell wall is an exterior wall layer that surrounds certain types of cells.It might be tough, flexible, or even rigid.
- A cell wall is a non-living component that covers the cell's outer layer. Its makeup varies per organism and is permeable.
- It protects the contents of the cell from the outside environment. It also gives the cell and its organelles form, support, and protection.
- Cellulose, hemicellulose, pectin, protein, and other substances are abundantly found in the cell wall.
Also read: Difference between Cell Membrane and Plasma Membrane
Cytoskeleton
The cytoskeleton is a component of the cytoplasm that offers internal support as well as aids in many forms of movement. It consists of a network of microtubules, microfilaments, and intermediate filaments that help with mechanical support and motility.
- Eukaryotic cells have a cytoskeleton composed of filamentous proteins giving mechanical support to the cell.
- It is inside the cytoplasm.
- All cytoskeletons are of three primary types of components that vary in size and protein content. These are microfilaments, microtubules, and fibres.
Endoplasmic Reticulum
The Endoplasmic Reticulum is a large organelle made up of tubules and membranous sheets that originate near the nucleus and extend throughout the cell. Many of a cell's products and packages are made and secreted by the endoplasmic reticulum.
Rough and Smooth Endoplasmic Reticulum
- The rough endoplasmic reticulum has a ribosome-studded surface, while the smooth endoplasmic reticulum has a smooth surface.
- These membranes fold continuously, finally connecting the nuclear membrane's outer layer. It is in every kind of eukaryotic cell except sperm cells and red blood cells.
Nucleus
The cell nucleus is a membrane-bound organelle present in eukaryotic cells. Usually, eukaryotic cells have a single nucleus
- Nearly the whole cell's genome is located in the nucleus.
- It appears that DNA and proteins make up the nucleoplasm in the nucleus.
- The nuclear envelope is of two membranes: the outer membrane and the inner membrane. These membranes allow molecules, ions, and RNA material to pass through.
- Ribosome formation also occurs within the nucleus.
Golgi Apparatus
The Golgi apparatus known as the Golgi complex or the Golgi body. They are membrane-bound organelles found in the cell's cytoplasm.
Structure of Golgi apparatus
- It is of flat, disc-shaped structures known as cisternae.
- They are deficient in plant sieve cells and human red blood cells.
- It is parallel and concentrically, near the nucleus.
- It is an ideal location for the production of glycoproteins and glycolipids.
Ribosomes
The Ribosome is a complicated structural molecular component found in cells.They can be found in both prokaryotic and eukaryotic cells.
- Ribosomes are found in eukaryotic cells either connected to the endoplasmic reticulum or in the cytoplasm.
- A ribosome is an intercellular structure composed of both RNA and protein that serves as the cell's centre of protein synthesis.
- The messenger RNA (mRNA) sequence is read by the ribosome, which then converts the genetic code into a specific string of amino acids that develop into extended chains and fold to make proteins.
Mitochondria
Mitochondria is a double membrane-bound organelle present in the cytoplasm of the cells of most Eukaryotic organisms.
Mitochondria
- Mitochondria have a double membrane structure and employ aerobic respiration to produce adenosine triphosphate (ATP).
- The adenosine triphosphate serves as a source of chemical energy throughout the cell due to which the mitochondria are also called the powerhouse of the cell.
- It is of an outer and an inner membrane. Folds are the inner membrane split by cristae.
- They aid in the control of cell metabolism.
Lysosomes
Lysosomes are membrane-enclosed organelles that contain an array of enzymes capable of degrading all biological polymers, including proteins, nucleic acids, carbohydrates, and lipids.
- Due to the presence of digesting enzymes, lysosomes are referred to as "suicidal bags."
- Lysosomes serve as the cell's digestive system, breaking down substances brought in from the outside and breaking down unused parts of the cell.
Also read: Difference between Lysosome and Ribosome
Plastids
The primary locations of photosynthesis in eukaryotic cells are organelles known as plastids. These are double-membrane structures found in plant cells. There are three kinds of these:
- Chloroplast is a chloroplast that contains chlorophyll and participates in photosynthesis.
- Chromoplasts contain carotene, a pigment that gives plants their yellow, red, or orange colours.
- Colourless leucoplasts store oil, fats, carbs, or proteins.
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Eukaryotic Cell Cycle
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During the cell cycle, eukaryotic cells divide. During the cell cycle, the cell goes through several phases. There are several checkpoints in between each stage.
Quiescence (G0)
The cell does not divide during this period, which is known as the resting phase. At this point, the cell cycle begins. Cells from the liver, kidney, neurons, and stomach all reach this stage. They can stay there for extended periods. Many cells never reach this stage and continue to divide forever throughout their lifespan.
Interphase
The cell goes through regular operations during interphase while simultaneously preparing for cell division. Many internal and external parameters must be satisfied for a cell to go from the interphase to the mitotic phase. The three interphase phases are known as G1, S, and G2.
- Gap 1 (G1) - The cell enlarges here. Protein levels rise as well.
- Synthesis (S) - DNA replication occurs at this step.
- Gap 2 (G2) - The cells grow even more in preparation for mitotic division.
Mitosis
Mitosis is a cell division stage of the cell cycle in which DNA in the nucleus cell is separated into two equal chromosome sets. As a result of cell division, genetically identical cells with the same number of chromosomes are created.
Mitosis involves the following stages.
- Prophase: The nuclear envelope begins to break into minute vesicles, and the membranous organelles fracture and spread toward the cell's borders during the first phase.
- Prometaphase: Prometaphase is the second phase of mitosis. The process by which the duplicated genetic material carried in the nucleus of a parent cell gets separated into two identical daughter cells. The nuclear envelope, the physical barrier that encloses nuclei, breaks away during prometaphase.
- Metaphase: The chromosomes condense and become distinct during mitosis or meiosis when they align in the middle of the dividing cell during metaphase. During karyotyping, these chromosomes are used.
- Anaphase: At the centromere, the cohesion proteins break down, and the sister chromatids split. Each chromatid, known as a chromosome, is drawn toward the centrosome linked to the microtubule. The cell grows noticeably longer (oval-shaped).
- Telophase: When the chromosomes reach the opposing poles, they begin to unravel, allowing them to relax into a chromatin structure. The mitotic spindles are depolymerized into tubulin monomers. These assemble into cytoskeletal components for each daughter cell.
- Cytokinesis: The second major step of the mitotic phase in cell division is accomplished by physically separating the cytoplasmic components into two daughter cells. The division is not complete until the cell components have been split and segregated into the two daughter cells.
Eukaryotic Cell Examples
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Protozoa, plants, fungi, and animals are examples of organisms based on the eukaryotic cell.
- Plant cells: The plant's cell wall is of cellulose, which provides support. It possesses a large vacuole that keeps the turgor pressure constant. Photosynthesis occurs in plant cells because they include chloroplasts.
Plant Cell Diagram
- Animal cells: They lack a cell wall because they have a cell membrane. It is because different animals have different forms. They can perform phagocytosis and pinocytosis.
Animal Cell Diagram
- Protozoa: Protozoans are unicellular organisms. Some protozoa have cilia for movement. A tiny coating of protection known as a pellicle protects the cell.
- Fungal cells: Chitin is present in the cell wall of fungus cells. Many fungi have holes called septa that allow cytoplasm and organelles to flow through.
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Things to Remember
- Eukaryotic cells include membrane-bound organelles and act as the basis for both unicellular and multicellular organisms.
- Eukaryotic cells primarily fall into two categories: animal cells and plant cells. Neurons, intestinal cells, and blood cells are examples of eukaryotic cells found in the human body.
- DNA is kept in double-stranded chromosomes that are compressed by histones in eukaryotic cells.
- Every eukaryote goes through a similar, but complicated process known as mitosis.
- The nucleus is referred to as the cell's control centre. It is a spherical structure with a membrane-bound that is present in eukaryotic cells.
Sample Questions
Ques. Are Eukaryotic cells unicellular or multicellular? (3 marks)
Ans. Eukaryotes are organisms whose cells have membrane-bound organelles in addition to a nucleus.
- Eukaryotic organisms come in a great variety, including most algae, all animals, plants, fungi, and protists.
- Eukaryotes can be single-celled or multicellular.
- Eukaryotes are distinguished from the prokaryotes group of organisms by the presence of internal membranes that divide certain eukaryotic cell components from the remainder of the cytoplasm.
- Organelles are the name for these membrane-bound structures.
Ques. Where are proteins synthesised inside the cell? (2 marks)
Ans. The proteins are produced on the Rough Endoplasmic Reticulum, which also houses the ribosomes. Protein synthesis takes place in ribosomes within a cell. One of the most important processes in a cell's life is protein synthesis since it not only creates the structural elements of the cell but also the enzymes that catalyse the production of the remaining organic macromolecules needed for life.
Ques. What is the endomembrane system? (3 marks)
Ans. A eukaryotic cell's endomembrane system is made up of several membranes (endomembranes) suspended in the cytoplasm.
These membranes separate the cell into organelles, which are structural and functional compartments. The nuclear membrane, the endoplasmic reticulum, the Golgi apparatus, lysosomes, vesicles, endosomes, and plasma (cell) membrane are among the organelles of the endomembrane system in eukaryotes.
A more precise definition of the system is the collection of membranes that together form a single functional and developmental unit and exchange materials directly or via vesicle transport.
Ques. What are the different types of protein elements present in the cytoskeleton? (3 marks)
Ans. Protein elements in the cytoskeleton are classified into three kinds.
- Microfilaments help cells move more easily by giving them stiffness and structure.
- Intermediate filaments carry tension and serve as anchors for the nucleus and other organelles.
- Microtubules assist the cell in resisting compression, act as vesicle-moving pathways for motor proteins, and pull replicated chromosomes to the opposite ends of dividing cells. Additionally, they make up the structural components of cilia, flagella, and centrioles.
Ques. How does a eukaryotic cell divide? (3 marks)
Ans. Eukaryotic cells, in particular, divide through the processes of mitosis and meiosis.
- Mitosis is a process shared by all eukaryotes in which a parent cell divides into two genetically identical daughter cells, each with the same number of chromosomes as the parent cell. During cell division, it passes through the following stages: Prophase, Metaphase, Anaphase, Telophase, and Cytokinesis.
- Meiosis, on the other hand, occurs solely in sexually reproducing eukaryotic creatures. The cells required for sexual reproduction divide during meiosis to form new cells known as gametes. Gametes have half the number of chromosomes as the other cells in the organism, and each gamete is genetically distinct because the parent cell's DNA is jumbled before the cell divides. This contributes to the uniqueness of the new organisms generated as a result of sexual reproduction.
Ques. What would happen to the life of a cell if there was no Golgi apparatus? (3 marks)
Ans. The Golgi apparatus is responsible for storing, modifying, and packaging products in vesicles.
- If there were no Golgi bodies, cells' proteins would float around randomly. Other cells and organs in the body would not function normally if the Golgi body did not distribute chemicals.
- There would be no lysosome production and the cell would eventually die as a result of a buildup of dead and damaged molecules and organelles.
- If the Golgi apparatus is not present, materials could not be packaged or delivered. Secretory functions in the cell would likewise stop.
- Without the Golgi apparatus, acrosome synthesis is impossible.
Ques. What would happen if the plasma membrane ruptures or breaks down? (3marks)
Ans. The plasma membrane acts as a selectively permeable wall between the inside of the cell and its environment. It keeps the inside of the cell intact by allowing only certain materials to enter and exit the cell. If the plasma membrane ruptures or breaks down, the cell will not exchange material with its surroundings through diffusion or osmosis. The protoplasmic substance will then vanish, and the cell will die.
Ques. Differentiate between the Rough Endoplasmic Reticulum and the Smooth Endoplasmic Reticulum. (5 marks)
Ans. The Rough endoplasmic reticulum and Smooth endoplasmic reticulum are differentiated on the following basis.
| Basis | Rough Endoplasmic Reticulum (RER) | Smooth Endoplasmic Reticulum (SER) |
|---|---|---|
| Meaning | Ribosomes are present in the rough endoplasmic reticulum's membrane. | Ribosomes are absent in the smooth endoplasmic reticulum's membrane. |
| Structure | Cisternae and a few tubules make up its structure. | Vesicles and tubules make up its structure. |
| Present | It is present close to the cytoplasm. | It is present close to the cell membrane. |
| Produces | Lysosomes are produced with the help of RER. | Spherosomes and oleosomes are produced by SER. |
| Made of | It is made up of cisternae. | It is made up of tubules. |
| Synthesise | Synthesise proteins and enzymes | Synthesise glycogen, lipids, and steroids. |
| Ribophorins | Ribophorins are absent. | It contains ribophorins and enables ribosome attachment to ER. |
Ques.Which Organelle is called the powerhouse of the cell and what is its function? (5 marks)
Ans. The cellular organelles known as mitochondria are responsible for releasing energy from food. This is referred to as cellular respiration. Because of this, mitochondria are frequently referred to as the cell's powerhouses. Cells that require a lot of energy, such as muscle cells, might have thousands of mitochondria.
- The cytoplasm undergoes several chemical events when the breakdown products from food digestion enter the cell. This enables some of the energy trapped in these products to be released and integrated into ATP, the cell's primary energy source (adenosine triphosphate).
- The remaining molecular pieces from this process then enter the mitochondria, where they undergo a lengthy process before being transformed into carbon dioxide and water. More ATP is created using the energy contained in these fragments. The cell can then employ the ATP molecules created in this way to provide the energy required to function.
Ques. How do cells track their development during the cell cycle? (5 marks)
Ans. A cell has to go through several checkpoints to transition from one stage of its life cycle to the next. Specialized proteins inspect each checkpoint to see if the required circumstances are there. If so, the cell can go on to the following stage. If not, the cell cycle stops moving forward. Errors in these checkpoints may result in cell death or cancer's uncontrolled development, both of which are devastating outcomes.
- For instance, the cell goes through a crucial checkpoint in the G1 phase that ensures the environment is favourable for replication. The cell could go into a resting stage known as G0 if circumstances are unfavourable. Some cells stay in G0 throughout the duration of the organism they are a part of. Mammal skeletal muscle cells and neurons, for instance, are normally in G0.
- In the final stages of the cell cycle, right before a cell enters mitosis from G2, there is another significant checkpoint. Here, a variety of proteins examine the DNA of the cell to make sure it is structurally sound and replicated appropriately. At this moment, the cell may stop to give the DNA time to repair itself, if necessary.
- Midway through mitosis, another crucial cell cycle checkpoint occurs. This examination evaluates if the cell's chromosomes are correctly linked to the spindle or the web of microtubules that will divide the cell when it divides. This procedure reduces the risk that the developing daughter cells may have aneuploidy, a condition in which the number of chromosomes is out of balance.
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