Protein synthesis
DNA, the carrier of hereditary information, is present in the nucleus. It contains the instructions necessary to manufacture all of our proteins. Since the precious DNA never leaves the nucleus, copies are made ( transcription) and directed towards the ribosomes, tiny factories, to be translated into proteins ( translation). Some of the proteins are then modified and assembled in the endoplasmic reticulum and transferred to the Golgi complex for further maturation, before being inserted in the cell membrane or excreted. The energy necessary to these processes is furnished by the mitochondria.
Visit the website Cells alive ! for details on cell components.
Example of animal cell: the mastocyte
Electron microscopy
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This white blood cell plays a role in allergy, wound healing and defence against pathogens. A: the whole cell. B: a section showing many granules rich in histamine and heparin.
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Mitochondrion
Electron microscopy
Golgi complex
Electron microscopy
Nucleus
Electron microscopy - © Kenneth M. Bart
The nucleolus is a specific region where ribosomes are produced. |
Chromosome
Electron microscopy
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Human cells contain 23 pairs of chromosomes, made of highly compacted DNA and proteins (chromatin).
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Chromosomes X and Y
Electron microscopy
The X and Y chromosomes are one of the 23 pairs of chromosomes of a human male cell. |
3D representation of a chromatin fibre,
made of compacted DNA and proteins
Courtesy of Joseph Roland
© 2003 - www.cytographica.com
3D representation of unpacked chromatin
Courtesy of Joseph Roland
© 2003 - www.cytographica.com
DNA double helix
The instructions contained in our DNA are assembled into “words” made of the “letters” A, T, G and C (bases). They will be “read” in order to elaborate the corresponding proteins. |
Tridimensional structure
of the DNA double helix
Molecular structure of DNA
The double helix is made of two identical backbones linked by pairs of complementary bases: adenine ⁄ thymine and guanine ⁄ cytosine. |
Transcription:
the messenger RNA factory
The enzyme RNA polymerase moves along the DNA strand and induces the formation of a complementary imprint, the messenger RNA (mRNA) molecule.
See a Flash movie on John Kyrk’s website. |
Migration of messenger RNA
The messenger RNA (mRNA) leaves the nucleus and enters the cytoplasm. The instructions it contains will be followed to make proteins.
3D model of a ribosome, the protein factory
Picture by K.Y. Sanbonmatsu, S. Joseph & C.-S. Tung
Translation: the protein factory
The instructions carried by the messenger RNA (mRNA) strand are “read” by a ribosome, a tiny protein factory. Each time a new “word” of 3 “letters” (bases) is read, a corresponding amino acid is brought by a specific transfer RNA (tRNA) and added to the growing protein. The empty tRNA then leaves and the ribosome moves 3 letters further.
See a Flash movie on John Kyrk’s website. |
“Ribbon” 3D model of a protein,
the enzyme RNA polymerase
The RNA polymerase (grey) is involved in the transcription process. It induces the synthesis of messenger RNA (blue) from DNA (red). |
Hemoglobin, a red blood cell protein
that carries oxygen
Membrane channel
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Proteins acting as channels allow molecules (red balls) to cross the cell membrane upon receiving a signal (green balls).
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3D model of an antibody
© Mike Clark
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The antibody binds an intruding virus or bacteria via its antigen binding sites.
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Cell skeleton
Fluorescent staining - Optical microscopy
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Tubulin (green) and actin (red) filaments are proteins of the cell “skeleton” (cytoskeleton). The DNA (blue) is in the nucleus.
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Main steps of the protein synthesis process.
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DNA from the Beginning |
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• Made at Cold Spring Harbor, provides extensive basics of DNA, genes and heredity. Small chapters with animations and illustrations offer a captivating introduction to a complex field. The French translation was made by scientists of the University of Geneva.
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Gene-ABC |
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• This website is proposed by the Swiss National Science Foundation in German, French and Italian. It's a playful exploration through all aspects of genetics. Here is the German version.
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John Kyrk |
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• John Kyrk is an american biologist, fond of animation and education. This website gathers together an exciting collection of Flash movies he made to demonstrate cell biology processes. A huge work, obviously.
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Cells alive ! |
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• This website represents 30 years of capturing film and computer-enhanced images of living cells and organisms for education and medical research. Thanks to Jim Sullivan, its owner.
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