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Questions and Answers
What are sarcomeres?
What are sarcomeres?
Repeating units of myofilaments that are found along the length of myofibrils
What is the function of a sarcomere?
What is the function of a sarcomere?
Muscle contraction and relaxation
What are four things that make up a sarcomere?
What are four things that make up a sarcomere?
Thick filaments, thin filaments, proteins that stabilize the position of the myofilaments, proteins that regulate interactions between the myofilaments
What is the main protein that makes up the thick filament of the sarcomere?
What is the main protein that makes up the thick filament of the sarcomere?
What is the main protein that makes up the thin filament of the sarcomere?
What is the main protein that makes up the thin filament of the sarcomere?
What are the two divisions of a sarcomere?
What are the two divisions of a sarcomere?
The A band is the ____ band?
The A band is the ____ band?
The I band is the ____ band?
The I band is the ____ band?
What are the three subdivisions of the A band?
What are the three subdivisions of the A band?
Where is the M line located?
Where is the M line located?
What are the two functions of the M line?
What are the two functions of the M line?
Where is the H band located?
Where is the H band located?
What types of filaments are found in the H band?
What types of filaments are found in the H band?
Where is the zone of overlap located?
Where is the zone of overlap located?
What types of filaments are found in the zone of overlap?
What types of filaments are found in the zone of overlap?
What types of filaments are found in the I band?
What types of filaments are found in the I band?
What structure bisects the I band?
What structure bisects the I band?
What are two proteins found at the Z line?
What are two proteins found at the Z line?
What is the function of actinin?
What is the function of actinin?
What is the function of titin?
What is the function of titin?
What are the four proteins that make up a thin filament?
What are the four proteins that make up a thin filament?
What does F-actin stand for?
What does F-actin stand for?
What protein is F-actin made up of?
What protein is F-actin made up of?
What is a structure found on G-actin?
What is a structure found on G-actin?
What is the active site on G-actin?
What is the active site on G-actin?
What is the function of nebulin?
What is the function of nebulin?
What is the function of tropomyosin?
What is the function of tropomyosin?
How many active sites can one molecule of tropomyosin cover?
How many active sites can one molecule of tropomyosin cover?
What other molecule is tropomyosin bound to?
What other molecule is tropomyosin bound to?
How many subunits does troponin contain?
How many subunits does troponin contain?
What are the functions of the three subunits of troponin?
What are the functions of the three subunits of troponin?
How many calcium ions can one troponin bind?
How many calcium ions can one troponin bind?
What type of molecules is a thick filament composed of?
What type of molecules is a thick filament composed of?
About how many myosin molecules make up a thick filament?
About how many myosin molecules make up a thick filament?
Describe the structure of a myosin molecule.
Describe the structure of a myosin molecule.
What is the function of the myosin tail?
What is the function of the myosin tail?
What is the function of the myosin head?
What is the function of the myosin head?
The ____ of a myosin molecule points toward the M line?
The ____ of a myosin molecule points toward the M line?
What is the connection between a myosin head and the active site on a thin filament called?
What is the connection between a myosin head and the active site on a thin filament called?
What protein is found at the core of a thick filament?
What protein is found at the core of a thick filament?
How do sarcomeres shorten?
How do sarcomeres shorten?
What is the sliding filament theory?
What is the sliding filament theory?
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Study Notes
Sarcomere Overview
- Sarcomeres are the basic structural units of muscle fibers, composed of myofilaments.
- Key functions include muscle contraction and relaxation.
Components of Sarcomeres
- Comprised of thick filaments (myosin) and thin filaments (actin).
- Stabilizing proteins maintain myofilament structure.
- Regulatory proteins oversee interactions between myofilaments.
Structural Divisions
- Two main divisions: A bands (dark) and I bands (light).
- A bands consist of three subdivisions: M line, H band, and zone of overlap.
M Line
- Located at the center of the A band.
- Connects and stabilizes neighboring thick filaments.
H Band
- Found on either side of the M line, contains only thick filaments.
Zone of Overlap
- Positioned at the outer edges of the A band, contains both thick and thin filaments.
I Band
- Contains only thin filaments and is bisected by the Z line, which features actinin and titin proteins.
Function of Z line Proteins
- Actinin connects adjacent thin filaments.
- Titin stabilizes filament positions and helps return sarcomere to resting length post-contraction.
Thin Filament Structure
- Made up of F-actin (filamentous actin), nebulin, tropomyosin, and troponin.
- F-actin consists of polymerized G-actin (globular actin), featuring an active site for myosin binding.
Troponin Complex
- Composed of three subunits: one binds tropomyosin, one binds G-actin, and one has a calcium receptor.
- Can bind two calcium ions, initiating contraction by moving tropomyosin and exposing active sites on G-actin.
Thick Filament Composition
- Composed primarily of 300 myosin molecules.
- Each myosin consists of a long tail and a head with two globular subunits.
Myosin Functionality
- Myosin tails bind to one another, forming thick filaments, while heads interact with active sites on thin filaments to form cross-bridges.
- Myosin heads facilitate muscle contraction by pulling on actin.
Muscle Contraction Mechanism
- Contraction occurs when myosin heads form cross-bridges with actin, pulling thin filaments towards the sarcomere’s center, leading to sarcomere shortening.
- This process is encapsulated in the sliding filament theory, asserting that thin filaments slide inward during contraction.
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