Eukaryotic Cell - Physical Characteristics, Membranes, Proteins And Membrane Transport, Signal Transduction, Metabolism, Mitochondrion, Chloroplast
cells specialized prokaryotic nucleus
All living organisms are composed of cells. A eukaryotic cell is a cell with a nucleus, which contains the cell's chromosomes. Plants, animals, protists, and fungi have eukaryotic cells, unlike the Eubacteria and Archaea, whose cells do not have nuclei and are therefore termed prokaryotic. In addition to having a nucleus, eukaryotic cells differ from prokaryotic cells in being larger and much more structurally and functionally complex. Eukaryotic cells contain subcompartments called organelles, which carry out specialized reactions within their boundaries. A eukaryotic cell may be an individual organism, such as the amoeba, or a highly specialized part of a multicellular organism, such as a neuron.
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A typical eukaryotic cell is about 25 micrometers in diameter, but this average hides a large range of sizes. The smallest cell is a type of green algae, Ostreococcus tauri, with a diameter of only 0.8 micrometers, about the size of a typical bacterium. The human sperm is about 4 micrometers wide, but 40 micrometers long, while the egg is about 100 micrometers in diameter. Single neurons can be a …
Proteins are long chains of amino acids. They have unique shapes and chemical properties that dictate their diverse functions. Proteins govern the range of materials that enter and leave the cell, relay signals from the environment to the interior, and participate in many metabolic reactions, harvesting or harnessing energy to transform raw materials into the molecules needed by the cell for growt…
Proteins, including membrane proteins, also play critical roles in signal transduction, or relay. Signals can include hormones, ions, environmental changes such as odors or light, or mechanical disturbances such as stretching. A hormone is a small molecule released by one cell in the body to influence the behavior of another. A hormone exerts its influence by binding to a protein receptor in the t…
Metabolism refers to the entire set of reactions within the cell. Most reactions can be classified as either anabolic or catabolic. Anabolic reactions use stored energy to build more complex molecules from simpler ones. Protein synthesis is an example. Catabolic reactions break down complex molecules to simpler ones, releasing energy in the process that may be harvested and stored by the cell. Glu…
Glucose breakdown begins in the cytosol, but the majority of the process occurs in the mitochondrion, the energy-harvesting organelle of the cell. In addition to participating in the breakdown of glucose (and making ATP in the process), the mitochondrion is also involved in breaking down fats and amino acids. All these fuels are processed in two major steps, termed the Krebs cycle and the electron…
Messenger RNA exported from the nucleus binds to a ribosome in the cytosol, which then proceeds to translate the genetic message into a protein. Some proteins, with their ribosomes, remain free in the cytosol throughout translation, but others do not. Those that do not remain free carry a special sequence of amino acids at their leading end, called a signal peptide. This sequence directs the growi…
Cells must reproduce in order for the organism to grow or repair damage. For single-celled organisms, cellular reproduction creates a new organism. Each new cell must get a complete set of chromosomes, which therefore must be duplicated and evenly divided between the two daughter cells. The orderly series of events involving cell growth and division is termed the cell cycle. Immediately following …
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