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Tropomyosin

Definition

noun

A long protein strand composed of two fully alpha helical chains in a coiled-coil dimmer, and binds along the length of the actin filament. It is also bound to bead-like protein complex (troponin) in which, together, they regulate the actin-myosin interations in muscle contraction.


Supplement

The tropomyosin, together with troponin, acts like a "molecular switch" that controls the interaction of actin and myosin.

In the absence of a nerve impulse, the tropomyosin lies fittingly on the groove of the actin filament, blocking the myosin-binding sites in actin. At this point the muscle is said to be relaxed or at rest. In the presence of nerve impulse, a cascade of reactions occurs that causes the release of calcium ions (from the sarcoplasmic reticulum). The calcium then binds to troponin, which causes a shift in the position of tropomyosin-troponin on the actin filament, unblocking the myosin-binding sites. This allows the myosin heads to bind with actin molecules, resulting in muscle shortening and contraction. Soon, the calcium levels become low again that the troponin-tropomyosin shifts back, blocking the myosin-binding sites again.


See also: troponin, actin filament


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Re: Muscle Contractions

... stimulates Ca2+ release from the sarcoplasmic reticulum to stimulate contraction (second messenger). The myosin fibers (on actin) are blocked by tropomyosin which is anchored by troponin. Ca2+ binds to troponin causing a conformational change thus moving tropomyosin allowing the myosin binding ...

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by Jpoley
Tue Mar 01, 2011 2:42 am
 
Forum: Human Biology
Topic: Muscle Contractions
Replies: 1
Views: 6713

Re: Cross Bridge Formation

... B, C Although you might get by saying calcium is the true regulator, its really calcium's presence and its interaction with troponin that allows tropomyosin to moved off the actin binding site.

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by wushufanatic
Fri Oct 23, 2009 10:13 pm
 
Forum: Human Biology
Topic: Cross Bridge Formation
Replies: 1
Views: 4323

Cross Bridge Formation

... incorrect but I disagree with my professor, so I was hoping to get some other opinions. Regulation of cross-bridge formation is accomplished by a. tropomyosin b. troponin c. calcium ions d. A and B e. A, B, and C

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by ArsenalV17btk
Fri Oct 23, 2009 6:35 pm
 
Forum: Human Biology
Topic: Cross Bridge Formation
Replies: 1
Views: 4323

MOTOR PROTIENS

look it up? Myosin, tropomyosin, and the like? Look up sarcomeres.... etc.

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by plasmodesmata11
Wed Mar 25, 2009 2:55 am
 
Forum: Cell Biology
Topic: MOTOR PROTIENS
Replies: 1
Views: 1986

Gene giving rise to Protein

The old dogma “one gene—one protein” is not always true for eucaryotic genes. For example, a single a-tropomyosin gene can produces multiple distinct mRNAs which then give rise to variant (but related) proteins. How does this occur? PLease can anyone answer this question?

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by Lurrena
Tue Mar 24, 2009 12:38 am
 
Forum: Cell Biology
Topic: Gene giving rise to Protein
Replies: 2
Views: 3235
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