The Role of Cytoplasm in a Cell

ancreatic cancer cells, SEM
Pancreatic cancer cells. Coloured scanning electron micrograph (SEM) of pancreatic cancer cells. The cells are joined by a cytoplasmic bridge. The irregular shape of the cells, the cellular projections and blebs (nodules) are typical of cancer cells. Pancreatic cancer often causes no symptoms until it is well established and untreatable. Science Photo Library - STEVE GSCHMEISSNER/ Brand X Pictures/ Getty Images

Cytoplasm consists of all of the contents outside of the nucleus and enclosed within the cell membrane of a cell. It is clear in color and has a gel-like appearance. Cytoplasm is composed mainly of water but also contains enzymes, salts, organelles, and various organic molecules.

Function

The cytoplasm functions to support and suspend organelles and cellular molecules. Many cellular processes also occur in the cytoplasm.

Some of these processes include protein synthesis, the first stage of cellular respiration (known as glycolysis), mitosis, and meiosis. In addition, the cytoplasm helps to move materials, such as hormones, around the cell and also dissolves cellular waste.

Divisions

The cytoplasm can be divided into two primary parts: the endoplasm (endo-,-plasm) and ectoplasm (ecto-,-plasm). The endoplasm is the central area of the cytoplasm that contains the organelles. The ectoplasm is the more gel-like peripheral portion of the cytoplasm of a cell.

Components

Prokaryotic cells, such as bacteria and archaeans, do not have a membrane-bound nucleus. In these cells, the cytoplasm consists of all of the contents of the cell inside the plasma membrane. In euckaryotic cells, such as plant and animal cells, the cytoplasm consists of three main components. They are the cytosol, organelles, and various particles and granules called cytoplasmic inclusions.

  • Cytosol: The cytosol is the semi-fluid component or liquid medium of a cell's cytoplasm. It is located outside of the nucleus and within the cell membrane.
  • Organelles: Organelles are tiny cellular structures that perform specific functions within a cell. Examples of organelles include: mitochondria, ribosomes, nucleus, lysosomes, chloroplasts, endoplasmic reticulum, and Golgi apparatus. Also located within the cytoplasm is the cytoskeleton, a network of fibers that help the cell maintain its shape and provide support for organelles.
  • Cytoplasmic Inclusions: Cytoplasmic inclusions are particles that are temporarily suspended in the cytoplasm. Inclusions consist of macromolecules and granules. Three types of inclusions found in the cytoplasm are secretory inclusions, nutritive inclusions, and pigment granules. Examples of secretory inclusions are proteins, enzymes, and acids. Glycogen (glucose storage molecule) and lipids are examples of nutritive inclusions. Melanin found in skin cells is an example of a pigment granule inclusion.

Streaming

Cytoplasmic streaming, or cyclosis, is a process by which substances are circulated within a cell. Cytoplasmic streaming occurs in a number of cell types including plant cells, amoebae, protozoa, and fungi. Cytoplasmic movement may be influenced by several factors including the presence of certain chemicals, hormones, or changes in light or temperature.

Plants employ cyclosis to shuttle chloroplasts to areas receiving the most available sunlight. Chloroplasts are the plant organelles responsible for photosynthesis and require light for the process. In protists, such as amoebae and slime molds, cytoplasmic streaming is used for locomotion. Temporary extensions of the cytoplasm known as pseudopodia are generated that are valuable for movement and capturing food.

Cytoplasmic streaming is also required for cell division as the cytoplasm must be distributed among daughter cells formed in mitosis and meiosis.

Cell Membrane

The cell membrane or plasma membrane is the structure that keeps cytoplasm from spilling out of a cell. This membrane is composed of phospholipids, which form a lipid bilayer that separates the contents of a cell from the extracellular fluid. The lipid bilayer is semi-permeable, meaning that only certain molecules are able to diffuse across the membrane to enter or exit the cell. Extracellular fluid, proteins, lipids, and other molecules may be added to a cell's cytoplasm by endocytosis. In this process, molecules and extracellular fluid are internalized as the membrane turns inward forming a vesicle. The vesicle encloses the fluid and molecules and buds off from the cell membrane forming an endosome.

The endosome moves within the cell to deliver its contents to their appropriate destinations. Substances are removed from the cytoplasm by exocytosis. In this process, vesicles budding from Golgi bodies fuse with the cell membrane expelling their contents from the cell. The cell membrane also provides structural support for a cell by serving as a stable platform for the attachment of the cytoskeleton and cell wall (in plants).

Sources:

  • “Cytoplasmic inclusions.” The Free Dictionary, Farlex, medical-dictionary.thefreedictionary.com/cytoplasmic inclusions.
  • “Ectoplasm.” The Free Dictionary, Farlex, medical-dictionary.thefreedictionary.com/ectoplasm.
  • “Endoplasm.” The Free Dictionary, Farlex, medical-dictionary.thefreedictionary.com/endoplasm.
  • Goldstein, Raymond E., and Jan-Willem van de Meent. “A physical perspective on cytoplasmic streaming.” Interface Focus, The Royal Society, 6 Aug. 2015, www.ncbi.nlm.nih.gov/pmc/articles/PMC4590424/.
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Bailey, Regina. "The Role of Cytoplasm in a Cell." ThoughtCo, Mar. 16, 2018, thoughtco.com/cytoplasm-defined-373301. Bailey, Regina. (2018, March 16). The Role of Cytoplasm in a Cell. Retrieved from https://www.thoughtco.com/cytoplasm-defined-373301 Bailey, Regina. "The Role of Cytoplasm in a Cell." ThoughtCo. https://www.thoughtco.com/cytoplasm-defined-373301 (accessed May 24, 2018).