The Cell

Prokaryotic vs. Eukaryotic Features

In biology, a cell is the basic structural, functional, and biological unit of all known living organisms. A cell is the smallest unit of life that can replicate independently, and can carry genetic material, which is in the form of DNA. Most commonly a cell is the smallest unit of a multicellular organism, however, unicellular organisms such as bacteria are also cells. The study of cells is called cell biology.

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The Cell

The Nucleus

The nucleus is the very dense region consisting of protons and neutrons at the center of an atom.

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The Cell

Ribosomes

In biology, a ribosome is a complex molecular machine, found within all living cells, that serves as the site of biological protein synthesis (translation). Ribosomes link amino acids together in the order specified by messenger RNA (mRNA) molecules. Ribosomes consist of two major components: the small ribosomal subunits and the large ribosomal subunits. Ribosomes are found in all domains of life, including archaea, bacteria and eukaryotes. The ribosome is often described as the central molecule of life, because it is the site of synthesis of proteins, which are essential for all cellular functions.

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The Cell

The Endomembrane System

The endomembrane system is a complex network of cell membranes that form sacs, tubes, and vesicles. It is responsible for transport of solutes, water, and macromolecules such as proteins and nucleic acids. It is composed of the endoplasmic reticulum, Golgi apparatus, lysosomes, peroxisomes, vacuoles, and the cytoskeleton. The endomembrane system is involved in many cellular processes such as secretion, cell signaling, cell motility, cell division, and cytokinesis.

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The Cell

Mitochondria and Chloroplasts

Mitochondria are organelles found in most eukaryotic organisms. They are the site of the Krebs cycle, where the oxidation of organic molecules releases usable energy. In addition to their importance in energy production, mitochondria are involved in other tasks, such as signaling, cellular differentiation, and cell death. Mitochondria have been implicated in several human diseases, including mitochondrial disorders, cardiac dysfunction, and cancer. Chloroplasts are the organelles in plant cells where photosynthesis takes place.

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The Cell

The Cytoskeleton

In cell biology, the cytoskeleton is a dynamic structure, composed of interlinking filaments, which extends throughout the cytoplasm. The cytoskeletal systems of different organisms are composed of similar proteins. These proteins include tubulin, actin and the various intermediate filaments. These proteins are highly dynamic and can interact to form structures such as filopodia, lamellipodia and podosomes.

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The Cell

The Extracellular World

In biology, the extracellular matrix (ECM) is a three-dimensional network of extracellular macromolecules, including collagens, proteoglycans, glycoproteins, and fibrous proteins, that provides structural and biochemical support to cells and tissues. It is composed of a heterogeneous mixture of macromolecules secreted by cells that is then assembled into a scaffold-like structure. The ECM is an integral part of the tissue structure and it provides the cells with support and a matrix for cell migration. The ECM is composed of structural and biochemical components including collagens, proteoglycans, glycosaminoglycans, fibronectin, laminins, nidogens, tenascins, and hyaluronan, among others. The ECM is composed of a matrix of macromolecules including proteins, glycoproteins, and polysaccharides.

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The Cell

Membrane Composition

The cell membrane is a lipid bilayer that separates the cell contents from the outside environment. It can be described as a selectively permeable membrane, because it allows some molecules to pass through it by diffusion and prevents others from doing so by being impermeable to them.

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The Cell

Membrane Proteins and Carbohydrates

A membrane protein is a protein that is embedded in a biological membrane. They are vital to many cellular functions such as cell signaling, transport of molecules and ions across the membrane, and other vital processes.

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The Cell

Membranes as Cellular Traffic Control

In cell biology, a membrane is a biological membrane, a lipid bilayer comprising a lipid membrane together with its associated proteins and carbohydrate constituents. It can be simple or complex, and can be of one or multiple layers. It can be of any size, and can be a single cell membrane or be part of a multicellular organism. It can form a protective barrier or be used as a filter. It can be involved in the transport of materials across it, by means of various transport proteins. In most cases, the membrane is a double layer, with different properties on each side. In animals, the two most common types are the plasma membrane and the nuclear membrane. The plasma membrane is the cell's outermost layer and is involved in maintaining the integrity of the cell. The nuclear membrane is a double membrane that envelops the cell nucleus and separates its contents from the cytoplasm.

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The Cell

Tool Talk - Microscopy

In cognitive linguistics, tool-being is the study of the conceptualization of tools in language. The term was coined by cognitive linguist George Lakoff and philosopher Mark Johnson in their book "Metaphors We Live By" (1980). Lakoff and Johnson argue that the conceptualization of tools in language is metaphorical, and that the metaphors that are used to conceptualize tools are based on the conceptualization of the human body, and of the human mind. The concept of tool-being is an important concept in cognitive linguistics, and is related to the concept of conceptual metaphor.

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