BIOTECH100
A Resource Guide to Investing in Biotechnology
Directory - Encyclopedia - Stock Index - Pipeline Drugs 

Biotechnology Encyclopedia

Cytoskeleton

The cytoskeleton is a cellular "scaffolding" or "skeleton" contained, as all other organelles, within the cytoplasm. It is a dynamic structure that maintains cell shape, enables some cell motion (using structures such as flagella and cilia), and plays important roles in both intra-cellular transport (the movement of vesicles and organelles, for example) and cellular division.

The eukaryotic cytoskeleton

Eukaryotic cells contain three kinds of cytoskeletal filaments.

Actin Filaments

Around 7 nm. in diameter, this filament is composed of two actin chains oriented in an helicoidal shape. They are mostly concentrated just beneath the plasma membrane, as they keep cellular shape, form cytoplasmatic protuberancies (like pseudopods and microvillus), participate in some cell-to-cell or cell-to-matrix junctions and the transduction of signals. They are also important for cytokinesis and, along with myosin, muscular contraction.

See also: actin, microfilaments

Intermediate Filaments

These 8 to 11 nanometers in diameter filaments are the more stable (strongly bound) and heterogenous constitutents of the cytoskeleton. They organize the internal tridimensional structure of the cell (they are structural components of the nuclear envelope or the sarcomeres for example). They also participate in some cell-cell and cell-matrix junctions.

Different intermediate filaments are:

See also: intermediate filaments

Microtubules

They are hollow cylinders of about 25 nm., formed by 13 protofilaments which, in turn, are polymers of alpha and beta tubulin. They have a very dynamic behaviour, binding GTP for polymerization, they are organized by the centrosome.

They play key roles in:

See also: microtubules

The prokaryotic cytoskeleton

The cytoskeleton was previously considered to be a feature only of eukaryotic cells, but recent research has revealed that homologues to all the major proteins of the eukaryotic cytoskeleton can also be found in prokaryotes. Although the evolutionary relationships are so distant that they are not obvious from protein sequence comparisons alone, the similarity of their three-dimensional structures provides strong evidence that the eukaryotic and prokaryotic cytoskeletons are truly homologous.

FtsZ

FtsZ, a relative of the eukaryotic tubulin, was the first protein of the prokaryotic cytoskeleton to be identified. Like tubulin, FtsZ forms filaments in the presence of GTP, but these filaments do not group into tubules. During cell division, FtsZ is the first protein to move to the division site, and is essential for recruiting other proteins that produce a new cell wall between the dividing cells.

MreB and ParM

Prokaryotic actin-like proteins, such as MreB, are involved in the maintenance of cell shape. All non-spherical bacteria have genes encoding actin-like proteins, and these proteins form a helical network beneath the cell membrane that guides the proteins involved in cell wall biosynthesis.

Some plasmids encode a partitioning system that involves an actin-like protein ParM. Filaments of ParM exhibit dynamic instability, and may partition plasmid DNA into the dividing daughter cells by a mechanism analogous to that used by microtubules during eukaryotic mitosis.

Crescentin

The bacterium Caulobacter crescentus contains a third protein, crescentin, that is related to the intermediate filaments of eukaryotic cells. Crescentin is also involved in maintaining cell shape, but the mechanism by which it does this is currently unclear.

External links

 
Biotech100 Index
What are the Requirements to be listed in the Biotech100 Index?
 Biotech100 list of companies
Pipeline drugs for the Biotech100


Clinical Trials
What is a Clinical Trial?
Phase I ,-- Phase II, -- PhaseIII
What is Randomized Control?
 What is a Double Blind Experiment?
What is the role of the FDA?


Investing in Stocks
Small Cap Stocks
Stocks and Bonds
Biotech100 Index


Sponsored Links


Careers and Employment
Biotechnology and Pharmaceutical
What are the Fastest Growing Careers?

Key Biotech Terms


Google
 
Web www.biotech100.com
SEARCH THE BIOTECH100 WEBSITE
  
     

 
All text is available under the terms of the GNU Free Documentation License (see Copyrights for details). Disclaimers. Wikipedia is powered by MediaWiki, an open source wiki engine..
 


Copyright 2005 BIOTECH100.COM. All rights reserved.

email: info@biotech100.com