Biochemsitry Books

Wednesday, March 5, 2008

Connective Tissue

Connective Tissue
Structure
Connective tissue is formed primarily of extracellular matrix,
consisting of ground substance, extracellular fluid, and fibers, in
which various connective tissue cells are embedded.
Function
Connective tissue supports organs and cells, acts as a medium for
exchange of nutrients and wastes between the blood and tissues,
protects against microorganisms, repairs damaged tissues, and stores
fat.
Extracellular Matrix.
The extracellular matrix provides a medium for the transfer of
nutrients and waste materials between connective tissue cells and the
bloodstream.
Ground substance
Ground substance is a colorless, transparent, gel-like material in
which the cells and fibers of connective tissue are embedded.
• It is a complex mixture of glycosaminoglycans, proteoglycans, and
Glycoproteins (see Chapter 4 for details on these components).
• Ground substance is a lubricant, helps prevent invasion of tissues
by foreign agents, and resists forces of compression.
Fibers
(collagen, reticular, and elastic) are long, slender protein polymers
present in different proportions in different types of connective
tissue.
Collagen fibers.
• There are at least 19 molecular types of collagen. The most common
collagen types in connective tissue proper are type I and type III
collagen, both consisting of many closely packed tropocollagen
fibrils. The average diameter of type I collagen fibrils is 75
nanometers (nm)
o Collagen fibers are produced in a two-stage process involving
intracellular events (within fibroblasts) and extracellular events.
o Collagen fibers have great tensile strength, which imparts both
flexibility and strength to tissues containing them.
o c. Bone, skin, cartilage, tendon, and many other structures of the
body contain collagen fibers.
Reticular fibers
• These are extremely thin [0.5-2.0 micrometers (um) in diameter] and
are composed primarily of type III collagen; they have a higher
carbohydrate content than other collagen fibers.
o Type III collagen fibers constitute the architectural framework of
certain organs and glands.
o Because of their high carbohydrate content, they stain black with
silver salts.
Elastic fibers
• These are coiled, branching fibers 0.2-1.0 um in diameter that
sometimes form loose networks.
o These fibers may be stretched up to 150% of their resting length.
o They are composed of microfibrils of elastin and fibrillin embedded
in amorphous elastin (see Chapter 4 III B).
o Elastic fibers require special staining in order to be observed by
light microscopy.

Myofibrils

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From: Text Books <rijuebook@gmail.com>
Date: Wed, 5 Mar 2008 21:50:48 +0530
Subject: Myofibrils
To: rijuebook.bscnursing@blogger.com
Myofilaments
Thin filaments
Thin filaments are composed of F-actin, tropomyosin, troponin, and
associated proteins.
F-actin
It is a polymer of G-actin monomers arranged in a double helix.
• Each monomer possesses an active site that can interact with mYOSIn.
• F-actin is present as filaments (with a diameter of5 nm) that
exhibit polarity, having a (+) and (-) end.
Tropomyosin
Tropomyosin molecules are 41 nm in length. They bind head-to-tail,
forming filaments that are located in the grooves of the F -actin
helix.
Troponin
Troponin is associated with each tropomyosin molecule and is composed of:
• Troponin T (TnT), which forms the tail of the molecule and functions
in binding the troponin complex to tropomyosin.
• Troponin C (TnC), which possesses four binding sites for calcium. It
may be related to calmodulin.
• Troponin I (TnI), which binds to actin, inhibiting interaction of
myosin and actin.
Nebulin
Nebulin is a long inelastic protein. Two nebulin molecules wrap around
each thin filament and assist in anchoring it to the Z disk.
• Each nebulin molecule is embedded in the Z disk by its carboxy
terminal, but does not span the entire Z disk.
• The amino terminal of each nebulin molecule ends in the A band, at
or near the free end of its thin filament.
• Nebulin in skeletal muscle is thought to determine the length of its
associated thin filament, although in cardiac muscle it extends only
one quarter of the length of the thin filament.
Thick filaments
Thick filaments each contain about 250 myosin molecules arranged in an
anti parallel fashion and three associated proteins-myomesin, titin,
and C protein.
Myosin
Myosin is composed of two identical heavy chains and two pairs of
light chains. The myosin molecule resembles a double-headed golf club.
• Myosin heavy chains consist of a long rod-like "tail" and a globular
"head." The tails of the heavy chains wind around each other in an
a-helical configuration.
o Tails function in the self-assembly of myosin molecules into bipolar
thick filaments.
o Actin-binding sites of the heads function in contraction.
• Myosin light chains are of two types; one molecule of each type is
associated with the globular head of each heavy chain.