Conservapedia - User contributions [en]

Ligand

2012-07-05T18:10:41Z

Nikolai: creating a ligand article

A ligand is a molecule that specifically binds to another molecule, often a larger one. Ligand binding usually causes a receptor protein to undergo a change of shape, which often activates the receptor. After activation, the receptor can then interact with other cellular molecules. <ref>Campbell, Neil A., and Jane B. Reece. Biology. San Francisco: Benjamin Cummings, 2002. Print.</ref>

==References==
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Cell signaling

2012-07-05T13:43:41Z

Nikolai: /* Long-distance signaling */

Cells in multicellular organisms usually communicate via chemical messengers targeted for cells that may or may not be immediately adjacent. This cell-cell communication is typically called cell signaling.

==Types of cell signaling==

There are two types of cell signaling -- local signaling and long distance signaling.

==Local signaling==

Local signaling occurs when cells communicate by direct contact. Plants and animals have cell junctions that directly connect the [[cytoplasm]] of adjacent cells. Thus, signaling substances may dissolve in the [[cytosol]] and pass freely between two cells.

Animal cells may also communicate through direct contact between membrane-bound molecules on a cell's surface, which occurs during a process called cell-cell recognition. This is important for embryonic development and the immune response.

In other cases, messenger molecules are secreted by the signaling cell. These [[local regulators]] travel only short distances and influence cells in their vicinity.

Ex: Growth factors, a type of local regular, stimulates nearby target cells to grow and divide. This type of local signaling is called [[paracrine signaling]].

==Long-distance signaling==

Chemicals called [[hormones]] are used for long-distance signaling. Hormones vary widely in molecular size and type, and usually travel via the circulatory system to target cells in other parts of the body.<ref>Campbell, Neil A., and Jane B. Reece. Biology. San Francisco: Benjamin Cummings, 2002. Print.</ref>

==References==
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Cell signaling

2012-07-05T13:42:45Z

Nikolai: creating a cell signaling artlces

Quorum sensing

2012-07-05T13:29:06Z

Nikolai: creating a quorum sensing article

Quorum sensing allows bacteria to sense the local density of bacterial cells. This is possible because cells of many bacterial species secrete small [[molecules]] that can be detected by other bacterial cells. The concentration of these signaling molecules is used in quorum sensing<ref>Campbell, Neil A., and Jane B. Reece. Biology. San Francisco: Benjamin Cummings, 2002. Print.</ref>

==References==
{{reflist}}

Light microscope

2012-07-05T13:20:22Z

Nikolai: reformatting

In a light microscope (LM), visible light is passed through the specimen and then through glass lenses. The lenses refract (bend) the light so that the image of the specimen is magnified. Light microscopes were first used by Renaissance scientists and are still widely used in biology.<ref>http://www.ruf.rice.edu/~bioslabs/methods/microscopy/microscopy.html</ref>

Some important parameters in [[microscopy]] are magnification and resolution. Magnification is the ratio of an object's image size to its real size. Resolution is a measure of the clarity of an object. Another important parameter is contrast, which accentuates differences in parts of the sample.<ref>Campbell, Neil A., and Jane B. Reece. Biology. San Francisco: Benjamin Cummings, 2002. Print.</ref>

The light microscope has a limited resolving power; it cannot resolve detail finer than .2 micrometers, or the size of a small [[bacterium]].

==References==
{{reflist}}

Light microscope

2012-07-05T13:19:34Z

Nikolai: creating a light microscope article

Light microscopes were first used by Renaissance scientists and are still widely used in biology.<ref>http://www.ruf.rice.edu/~bioslabs/methods/microscopy/microscopy.html</ref> In a light microscope (LM), visible light is passed through the specimen and then through glass lenses. The lenses refract(bend) the light so that the image of the specimen is magnified.

Some important parameters in [[microscopy]] are magnification and resolution. Magnification is the ratio of an object's image size to its real size. Resolution is a measure of the clarity of an object. Another important parameter is contrast, which accentuates differences in parts of the sample.<ref>Campbell, Neil A., and Jane B. Reece. Biology. San Francisco: Benjamin Cummings, 2002. Print.</ref>

The light microscope has a limited resolving power; it cannot resolve detail finer than .2 micrometers, or the size of a small [[bacterium]].

==References==
{{reflist}}

Compound

2012-07-05T13:09:50Z

Nikolai: fixing the footnote on my edit

A '''compound''' is a [[molecule]] which is composed of more than one [[element]].
<ref>A compound is a substance with a fixed ratio of elements which determines the composition, and a particular organization which determines chemical properties. [http://www.newworldencyclopedia.org/entry/Chemical#Compounds New World Encyclopedia] </ref> Table salt, for example, is sodium chloride (NaCl), a compound composed of the elements sodium (Na) and chlorine (Cl) in a 1:1 ratio. Pure sodiun is a metal, and pure chlorine is a poisonous gas. When chemically combined, however, sodium and chlorine form an edible compound. This is a simple example of organized [[matter]] having emergent properties: A compound has characteristics different from those of its elements.<ref>Reece, Jane B., and Neil A. Campbell. Campbell Biology / Jane B. Reece ... [et Al.].</ref>

Chemical compounds can be fairly simple, such as water (H2O), which is just one [[oxygen]] atom and two [[hydrogen]] atoms. Many are moderately complex, like sugars, which consist of no more than a few dozen [[carbon]], oxygen, and hydrogen atoms, e.g. C6H12O6. Some are relatively huge (still not visible to the naked eye), such as DNA, which can contain millions of atoms in one double helix crystal.

In general, compounds containing carbon are referred to as "[[organic chemistry|organic compounds]]".

==Notes==
<references/>

[[Category:Chemistry]]

Compound

2012-07-03T19:16:46Z

Nikolai: adding more detail

A '''compound''' is a [[molecule]] which is composed of more than one [[element]].
<ref>A compound is a substance with a fixed ratio of elements which determines the composition, and a particular organization which determines chemical properties. [http://www.newworldencyclopedia.org/entry/Chemical#Compounds New World Encyclopedia] </ref> Table salt, for example, is sodium chloride (NaCl), a compound composed of the elements sodium (Na) and chlorine (Cl) in a 1:1 ratio. Pure sodiun is a metal, and pure chlorine is a poisonous gas. When chemically combined, however, sodium and chlorine form an edible compound. This is a simple example of organized [[matter]] having emergent properties: A compound has characteristics different from those of its elements.[Reece, Jane B., and Neil A. Campbell. Campbell Biology / Jane B. Reece ... [et Al.].]</ref>

Chemical compounds can be fairly simple, such as water (H2O), which is just one [[oxygen]] atom and two [[hydrogen]] atoms. Many are moderately complex, like sugars, which consist of no more than a few dozen [[carbon]], oxygen, and hydrogen atoms, e.g. C6H12O6. Some are relatively huge (still not visible to the naked eye), such as DNA, which can contain millions of atoms in one double helix crystal.

In general, compounds containing carbon are referred to as "[[organic chemistry|organic compounds]]".

==Notes==
<references/>

[[Category:Chemistry]]