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- Nucleus. In eukaryotic organisms, the nucleus (plural: nuclei) is known to be the control center of the cell. It houses the cell’s genome (genetic material), where the processes such as DNA replication, transcription, and RNA processing occur.
- Cell Membrane (also Plasma Membrane) Like any other membranes, the cell membrane is composed of a phospholipid bilayer (also described as the Fluid Mosaic Model) that creates a rigid barrier between the inside of the cell and its outside environment.
- Cytoplasm. By definition, the cytoplasm is the fluid that fills the cell up and is surrounded by the cell membrane. The cytoplasm is mainly composed of salts and proteins dissolved in water.
- Cell Wall. The outer covering of cells (plants, fungi, algae, bacteria, and archaea) located next to the cell membranes is called the cell wall. While the cell membrane is made up of phospholipids, the cell wall is made up of sturdier compounds – polysaccharides, usually cellulose (in plants) and peptidoglycan (in bacteria).
Learn about the different levels of cellular organization, such as cell membrane, cell wall, nucleus, and organelles. Find out how they function and how they are related to endosymbiosis and energy production.
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Aug 31, 2023 · Based on the organization of their cellular structures, all living cells can be divided into two groups: prokaryotic and eukaryotic (also spelled procaryotic and eucaryotic). Animals, plants, fungi, protozoans, and algae all possess eukaryotic cell types.
Learn how cells are organized into tissues, organs, and organ systems in multicellular organisms. Explore the evolution and diversity of cellular organization from single-celled to colonial to multicellular forms.
- Overview
- The nature and function of cells
- The molecules of cells
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A cell is a mass of cytoplasm that is bound externally by a cell membrane. Usually microscopic in size, cells are the smallest structural units of living matter and compose all living things. Most cells have one or more nuclei and other organelles that carry out a variety of tasks. Some single cells are complete organisms, such as a bacterium or yeast. Others are specialized building blocks of multicellular organisms, such as plants and animals.
What is cell theory?
Cell theory states that the cell is the fundamental structural and functional unit of living matter. In 1839 German physiologist Theodor Schwann and German botanist Matthias Schleiden promulgated that cells are the “elementary particles of organisms” in both plants and animals and recognized that some organisms are unicellular and others multicellular. This theory marked a great conceptual advance in biology and resulted in renewed attention to the living processes that go on in cells.
What do cell membranes do?
The cell membrane surrounds every living cell and delimits the cell from the surrounding environment. It serves as a barrier to keep the contents of the cell in and unwanted substances out. It also functions as a gate to both actively and passively move essential nutrients into the cell and waste products out of it. Certain proteins in the cell membrane are involved with cell-to-cell communication and help the cell to respond to changes in its environment.
cell, in biology, the basic membrane-bound unit that contains the fundamental molecules of life and of which all living things are composed. A single cell is often a complete organism in itself, such as a bacterium or yeast. Other cells acquire specialized functions as they mature. These cells cooperate with other specialized cells and become the building blocks of large multicellular organisms, such as humans and other animals. Although cells are much larger than atoms, they are still very small. The smallest known cells are a group of tiny bacteria called mycoplasmas; some of these single-celled organisms are spheres as small as 0.2 μm in diameter (1μm = about 0.000039 inch), with a total mass of 10−14 gram—equal to that of 8,000,000,000 hydrogen atoms. Cells of humans typically have a mass 400,000 times larger than the mass of a single mycoplasma bacterium, but even human cells are only about 20 μm across. It would require a sheet of about 10,000 human cells to cover the head of a pin, and each human organism is composed of more than 30,000,000,000,000 cells.
A cell is enclosed by a plasma membrane, which forms a selective barrier that allows nutrients to enter and waste products to leave. The interior of the cell is organized into many specialized compartments, or organelles, each surrounded by a separate membrane. One major organelle, the nucleus, contains the genetic information necessary for cell growth and reproduction. Each cell contains only one nucleus, whereas other types of organelles are present in multiple copies in the cellular contents, or cytoplasm. Organelles include mitochondria, which are responsible for the energy transactions necessary for cell survival; lysosomes, which digest unwanted materials within the cell; and the endoplasmic reticulum and the Golgi apparatus, which play important roles in the internal organization of the cell by synthesizing selected molecules and then processing, sorting, and directing them to their proper locations. In addition, plant cells contain chloroplasts, which are responsible for photosynthesis, whereby the energy of sunlight is used to convert molecules of carbon dioxide (CO2) and water (H2O) into carbohydrates. Between all these organelles is the space in the cytoplasm called the cytosol. The cytosol contains an organized framework of fibrous molecules that constitute the cytoskeleton, which gives a cell its shape, enables organelles to move within the cell, and provides a mechanism by which the cell itself can move. The cytosol also contains more than 10,000 different kinds of molecules that are involved in cellular biosynthesis, the process of making large biological molecules from small ones.
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Specialized organelles are a characteristic of cells of organisms known as eukaryotes. In contrast, cells of organisms known as prokaryotes do not contain organelles and are generally smaller than eukaryotic cells. However, all cells share strong similarities in biochemical function.
Cells contain a special collection of molecules that are enclosed by a membrane. These molecules give cells the ability to grow and reproduce. The overall process of cellular reproduction occurs in two steps: cell growth and cell division. During cell growth, the cell ingests certain molecules from its surroundings by selectively carrying them through its cell membrane. Once inside the cell, these molecules are subjected to the action of highly specialized, large, elaborately folded molecules called enzymes. Enzymes act as catalysts by binding to ingested molecules and regulating the rate at which they are chemically altered. These chemical alterations make the molecules more useful to the cell. Unlike the ingested molecules, catalysts are not chemically altered themselves during the reaction, allowing one catalyst to regulate a specific chemical reaction in many molecules.
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Biological catalysts create chains of reactions. In other words, a molecule chemically transformed by one catalyst serves as the starting material, or substrate, of a second catalyst and so on. In this way, catalysts use the small molecules brought into the cell from the outside environment to create increasingly complex reaction products. These products are used for cell growth and the replication of genetic material. Once the genetic material has been copied and there are sufficient molecules to support cell division, the cell divides to create two daughter cells. Through many such cycles of cell growth and division, each parent cell can give rise to millions of daughter cells, in the process converting large amounts of inanimate matter into biologically active molecules.
Learn about the basic unit of life, the cell, and its structure, functions, and diversity. Explore the similarities and differences between animal and plant cells, and the organelles and processes that enable them to survive and reproduce.
Learn about the structure and functions of the cell membrane, cytoplasm, nucleus, and cytoskeleton. Explore the roles of cilia, flagella, microtubules, microfilaments, and intermediate filaments in cellular processes.
Feb 28, 2021 · Learn about the structure and function of cells, the basic units of life, and how they differentiate and perform homeostasis. Explore the cell membrane, cytoplasm, nucleus, cell cycle, and cell types in the human body.
