10.3 Sarcomere Anatomy and Function Flashcards

Questions and Answers

What are sarcomeres?

Repeating units of myofilaments that are found along the length of myofibrils

What is the function of a sarcomere?

Muscle contraction and relaxation

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?

Myosin Signup and view all the answers

What is the main protein that makes up the thin filament of the sarcomere?

Actin Signup and view all the answers

What are the two divisions of a sarcomere?

A bands, I bands Signup and view all the answers

The A band is the ____ band?

Dark Signup and view all the answers

The I band is the ____ band?

Light Signup and view all the answers

What are the three subdivisions of the A band?

M line, H band, zone of overlap Signup and view all the answers

Where is the M line located?

The center of the A band Signup and view all the answers

What are the two functions of the M line?

Connects neighboring thick filaments together, stabilizes the positions of the thick filaments Signup and view all the answers

Where is the H band located?

On either side of the M line Signup and view all the answers

What types of filaments are found in the H band?

Only thick filaments Signup and view all the answers

Where is the zone of overlap located?

On the outer edges of the A band Signup and view all the answers

What types of filaments are found in the zone of overlap?

Thick and thin filaments Signup and view all the answers

What types of filaments are found in the I band?

Only thin filaments Signup and view all the answers

What structure bisects the I band?

The Z line Signup and view all the answers

What are two proteins found at the Z line?

Actinin, titin Signup and view all the answers

What is the function of actinin?

Connects the neighboring thin filaments together Signup and view all the answers

What is the function of titin?

Stabilizes the positions of the thick and thin filaments, restores resting sarcomere length after contraction Signup and view all the answers

What are the four proteins that make up a thin filament?

F-actin, nebulin, tropomyosin, troponin Signup and view all the answers

What does F-actin stand for?

Filamentous actin Signup and view all the answers

What protein is F-actin made up of?

G-actin Signup and view all the answers

What is a structure found on G-actin?

Active site Signup and view all the answers

What is the active site on G-actin?

It is the binding site for myosin from the thick filament Signup and view all the answers

What is the function of nebulin?

Holds the F-actin together Signup and view all the answers

What is the function of tropomyosin?

It blocks the active sites on G-actin and prevents myosin from binding Signup and view all the answers

How many active sites can one molecule of tropomyosin cover?

Seven Signup and view all the answers

What other molecule is tropomyosin bound to?

Troponin Signup and view all the answers

How many subunits does troponin contain?

Three Signup and view all the answers

What are the functions of the three subunits of troponin?

One subunit binds to tropomyosin, one subunit bonds to a G-actin, one subunit has a calcium receptor Signup and view all the answers

How many calcium ions can one troponin bind?

Two Signup and view all the answers

What type of molecules is a thick filament composed of?

Myosin molecules Signup and view all the answers

About how many myosin molecules make up a thick filament?

300 Signup and view all the answers

Describe the structure of a myosin molecule.

Composed of two subunits twisted around one another, has a long tail and a free head composed of two globular protein subunits Signup and view all the answers

What is the function of the myosin tail?

It binds to other myosin molecules in the thick filament Signup and view all the answers

What is the function of the myosin head?

Binds with the active site on a thin filament Signup and view all the answers

The ____ of a myosin molecule points toward the M line?

Tail Signup and view all the answers

What is the connection between a myosin head and the active site on a thin filament called?

Cross-bridge Signup and view all the answers

What protein is found at the core of a thick filament?

Titin Signup and view all the answers

How do sarcomeres shorten?

Myosin heads bind and form a cross-bridge with actin molecules. The myosin heads then pull on the actin molecules, causing them to slide along the myosin filaments. Thus, sarcomeres shorten. Signup and view all the answers

What is the sliding filament theory?

A theory that postulates that the thin filaments slide toward the center of a sarcomere during muscle contraction Signup and view all the answers

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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Description

Explore the essential components and functions of sarcomeres with this set of flashcards. Learn about the anatomy of these crucial myofilament units and their role in muscle contraction and relaxation. Great for students studying muscle physiology and anatomy.