Introduction to cell biology – Its types and structure


                   Cell biology is the branch of biology that deals with the study of cells. It is also termed “cytology.” Cell structure, function, and behavior all come under cell biology.


         A cell is the first level of living organization. It is the fundamental building block of life. It comprises all species referred to as “multicellular organisms” A cell is the smallest and essential life unit that carries life’s importance in various activities. Cells are said to be building blocks of life as they replicate themselves independently.


                                Cell biology began with the discovery of the cell. Many scientists played a major role in discovering cells. The cell was discovered by Robert Hook in 1665 by using dead plant material and examined it under the microscope and found compartments which is a space he named “CELLS”. In 1831 Robert Brown reported that the cell nucleus is present, so Robert Hook’s perspective about empty spaces changed.


                  Theodor Schwann and Schleiden worked on “Cell theory”. They concluded their work that plants and animals were made up of cells. While another scientist Rudolph Virchow said that cells can produce new cells by cell division.


  1. Cells make up all living things.
  2. Cells are the structural and functional unit of all organisms.
  3. Cells can produce new cells by cell division.


                   Cells are in diverse forms like skin cells, nerve cells, bacterial cells, plant cells, etc. Our body has red blood cells, white blood cells, mast cells, etc. Cell diversity can be based on:

  • Number of cells
  • Size
  • Shape


           The number of cells may vary from organism to organism in the level of organization. They are unicellular and multicellular.


            Any organism which is composed of single-cell is unicellular like bacteria, yeast, paramecium, and amoeba. They are microscopic.


            Any organism which is composed of more than one cell is said to be multicellular. It includes eukaryotes only like plants, animals, humans, etc. They are macroscopic.


             They vary from cell to cell with the function of cells. They can be regular and irregular in shape, circular or rectangular, etc. The size of the cell can be as small as 0.0001mm and large as 12 inches.


  •  Prokaryotic cell
  •   Eukaryotic cell


            Prokaryotic cells lack membrane bound nuclei. They have genetic material DNA circular in shape which is present in the cytoplasm. structure of Bacteria, archaea, and blue-green algae(cyanobacteria) are different from eukaryotes. They consist of cell walls which help in protecting and maintaining the cell and its shape. The bacterial cell wall is made up of peptidoglycan as compared to archaea with no peptidoglycan. The cell size ranges from 0.1 to 0.5 micrometers. They can reproduce by binary fission.


              Eukaryotic cells consist of a well-defined membrane-bounded nucleus with linear shape DNA. Their size ranges from 10 to 100 micrometers. They have organelles present as compared to prokaryotes. They are more complex than prokaryotes and can reproduce sexually and asexually. Animals, plants, fungi, and protists are present in eukaryotic cells.


The cell consists of a Cell membrane, cytoplasm, cell wall, nucleus, and cell organelles.


                            The cell membrane also termed the plasma membrane is the outermost covering of a cell composed of lipids, proteins, and some carbohydrates. Cell membrane helps in protecting cells and in transportation. It also helps in the process of phagocytosis.


                            The cell wall is mainly present in plant cells composed of cellulose, hemicellulose, and pectin. It protects the cell membrane and maintains the cell shape.


                            The cytoplasm is present inside the plasma membrane. It consists of cytosol which is a jelly-like soluble part in the cytoplasm. Cytoplasm acts as a storage for different chemicals and with some metabolic reactions.


                            The nucleus is the largest membrane-enclosed organelle in the cell which contains the chromosomes and heredity material DNA. Its size ranges from 5 to 10 m. Its function possesses in cell division and protein synthesis.


Cell organelles with their respective functions are as follows:


          Ribosomes are the factory of proteins. They are found as tiny granules found in the cytosol of the cytoplasm. They are made of ribosomal RNA and proteins.


         ER is a network of connections or channels that is in contact with the plasma membrane and nuclear membrane. It consists of:

  • Rough ER gives a rough appearance when ribosomes are attached to membranes and act as protein synthesis.
  • Smooth ER act as lipid synthesis in the membrane and Functions as calcium storage. The attachment of ribosomes is few in smooth ER.


        Golgi bodies are membrane-bound organelles with a flattened stack-like structure. Its flattened part is called cisternae which is 4 to 8 in Golgi bodies. They function in transportation and secretions. They also help in granule formation. These bodies take protein from ER and transport them to their respective places. Golgi bodies’ main importance is that they modify the proteins and lipids into glycoproteins or glycolipids.


         Lysosomes are membrane-bound vesicles that consist of digestive enzymes. Their function is to digest all types of large molecules(macromolecules) with the help of phagocytosis. They contain hydrolytic enzymes like hydrolases.


           Mitochondria are also termed chondrocytes and it’s the essential organelle of eukaryotic cells. They are double bounded membranes, the outer membrane contains pores and is smooth while the inner membrane contains infoldings called cristae. It is a powerhouse of a cell as it forms ATP as an energy source. The function of mitochondria is to convert food into ATP.


            Microbodies is membrane-bound vesicles that contain several enzymes and are present in both animal and plant cell. They are peroxisomes and glyoxisomes.


                        Peroxisomes are organelles present in the cytoplasm which contains hydrogen peroxide. It produces oxidases and catalases in a cell. Its diameter is about 5 micrometers. Their function is to in lipids synthesis and the formation of hydrogen peroxide.


                 Glyoxisomes is plant organelle not present in animal cells. They contain glycolic acid oxidases and catalases. They are involved in the glycolate cycle. Glyoxisomes function in converting fatty acids into carbohydrates and in the seed germinating process.


                    Plant cells are eukaryotic cells and are surrounded by a cell wall. Similarly, there are organelles present with many cellular activities. The organelles are as follows:


           Vacuoles are present in both plant and animal cells but large in plant cells. Vacuoles are membrane-bounded organelles with space that is used for disposing of various substances. Their function is to store food, water, or other waste materials in cells for survival. The plant cell has a larger vacuole as they require a large number of nutrients for making the cell function properly.


            Plastids are membrane-bound organelles that have pigment bodies. They have their DNA. Plastids are only present in plant cells. There are three main types chloroplast, chromoplast, and leucoplast.


           Chloroplast is a green pigment membrane-bound structure which varies in shape and size with a diameter of 4 to 6 micrometers. They contain chlorophyll which is used to absorb light energy and utilizes to manufacture food. It mainly helps in photosynthesis. Its main components are the envelope, the stroma, and the thylakoid. The envelope is a double membrane while the stroma is fluid that surrounds the thylakoid. Chloroplast can self-replicate.


          Chromoplast is a colored plastid that functions to impart colors to plants other than green. They mainly provide color to flowers and ripened fruits. They play role in pollination and seed dispersal.


           Leucoplast is a non-photosynthetic organelle that is colorless. They are tubular and are helps in storing food.


            The cytoskeleton is one of the organelles of cell present inside the cytoplasm. They lack membranes and are formed of microtubules, microfilaments, and intermediate filaments. Their function is in maintaining cell shape, movement, and in cell division.


            The centriole is an animal organelle located near the outer surface of the nucleus. They play a major role in cell division and the formation of cilia. The cell division here is called Mitosis in which two daughter cells are genetically produced by one parent cell.


            Cell division is a process of dividing cells and making new cells. Cell division is a larger cell cycle consisting of two types.


            This is a bacterial cell division that helps in binary fission. Binary fission is a process of dividing two new identical cells by asexual reproduction.


             This cell division consists of Mitosis and Meiosis.


              Mitosis is a cell duplicating process in which two daughter cells are created by one single parent cell. Its function is to replace the damaged cells and the growth of cells


              Meiosis is a process of dividing a single cell into four cells with genetic information sexually. Egg cells and sperm are involved in meiosis.


               The cell cycle is a series of steps that are involved in cell duplication. The eukaryotic cell cycle consists of the Interphase and M phase.


                This is the resting step of the cell where the cell is preparing for replication. It has different phases which help metabolically in replication.

  • G1 phase
  • S phase
  • G2 phase


               M phase is the mitotic phase which consists of:

  • Prophase
  • Metaphase
  • Anaphase
  • Telophase


Mubashir Iqbal
Mubashir Iqbal

Mubashir Iqbal is a highly dedicated and motivated Microbiologist with an MPhil in Microbiology from the University of Veterinary and Animal Sciences. Currently, he is researching the efficacy of commercially available SARS Cov-2 vaccines to neutralize the omicron variant in Pakistan. He holds a Bachelor's degree in Microbiology and has experience in chemical and microbiological analysis of water samples, managing SOPs and documents according to standard ISO 17025. Additionally, he has worked as an internee in BSL 3, Institute of Microbiology, UVAS, where he gained experience in RNA extraction, sample processing, and microscopy.

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