MODULE 5: Chapter 6.4 Flashcards
What is the breakthrough idea regarding muscle contraction proposed in 1954?
The sliding filament model, explaining how muscle fibers slide past one another during contraction
Proposed by Andrew Huxley and Rolf Niedergerke, and by Hugh Huxley and Jean Hanson.
What are the two primary proteins involved in muscle contraction?
- Actin
- Myosin
What does the sliding filament model state?
Muscle filaments, consisting of actin and myosin proteins, slide over one another during muscle contraction using chemical energy from ATP hydrolysis.
What are myoblasts?
Large fused cells that make up muscle tissue, containing many nuclei and sharing a common plasma membrane.
What is the sarcolemma?
The common plasma membrane shared by myoblasts in muscle cells.
What is the role of T tubules in muscle cells?
They provide the necessary exchange of extracellular O2 and nutrients required for muscle contraction.
What is the primary active transporter in the sarcoplasmic reticulum?
SERCA, which is critical for modulating intracellular Ca2⁺ levels.
What is a sarcomere?
The repeating unit in skeletal muscle formed by the overlapping arrangement of thick and thin filaments.
What proteins are found in thick filaments?
Myosin protein subunits.
What proteins are found in thin filaments?
- Actin
- Tropomyosin
- Troponin
What is the function of Z-disk proteins in muscle fibers?
They serve as anchors for thick and thin filaments to permit muscle contraction.
How do thick filaments form?
Individual thick filaments contain hundreds of myosin molecules arranged with fibrous tails in the middle and globular heads at either end.
What is tropomyosin’s role in thin filaments?
It is a coiled coil α-helical protein that associates with actin and regulates myosin binding.
What is the function of the troponin complex?
It regulates Ca2⁺ and mediates muscle contraction.
What does the I band in a sarcomere represent?
The locations of thin filaments.
What is the A band in a sarcomere?
A region consisting of thick filaments and overlapping thick and thin filaments.
What happens during muscle contraction in terms of Z disks?
The Z-disk proteins are brought closer together as thick and thin filaments slide past one another.
What initiates muscle contraction?
Neuronal stimulation of muscle cells at neuromuscular junctions, leading to Ca2⁺ release from the sarcoplasmic reticulum.
What is the role of Ca2⁺ in muscle contraction?
It binds to troponin, causing conformational changes that allow myosin binding to actin.
How does ATP hydrolysis affect muscle contraction?
It drives conformational changes in myosin, allowing it to bind to actin.
What are the five steps of the actin–myosin reaction cycle?
- Myosin heads bind to actin subunits
- Release of Pi causes power stroke
- ADP is released
- ATP binds to myosin, causing release from actin
- ATP hydrolysis induces recovery conformation
What happens during muscle relaxation?
Ca2⁺ levels decrease, blocking myosin binding sites on actin.
What causes myosin to disengage from the actin filament?
ATP binds to the myosin head
This binding causes a conformational change that leads to myosin detaching from actin.
What is the role of ATP hydrolysis in the myosin head?
Induces the recovery conformation
This prepares the myosin head for another round of the reaction cycle.
What leads to muscle relaxation?
Termination of neuromuscular signals and decrease in Ca2⁺ levels
This is facilitated by SERCA-mediated active transport.
What happens to myosin binding sites on actin during muscle relaxation?
They are blocked
This blocking occurs when Ca2⁺ levels decrease.
What occurs when the thick and thin filaments slip past one another?
The sarcomere returns to its elongated state
This process is aided by the uncoiling of the titin spring protein.
What are the distinct molecular events in the actin–myosin reaction cycle?
ATP binding, hydrolysis, dissociation of ADP and Pi
Each step has unique functions in muscle contraction.
What does ATP binding to the myosin head cause?
Dissociation from the actin thin filament
This is the first step in the actin–myosin reaction cycle.
What happens after ATP hydrolysis in the myosin head?
A conformational change occurs
This change positions the myosin head for the next contraction.
Under what condition are myosin binding sites on actin uncovered?
When Ca2⁺ levels in the cell are elevated
This is initiated by neuromuscular signaling.
What is released during the power-stroke conformation of the myosin head?
Pi (inorganic phosphate)
This release is crucial for muscle contraction.
What does the myosin head do during the power stroke?
Pulls the actin filament 70 Å along the myosin filament
This action is responsible for muscle contraction.
What happens to ADP in the myosin head after the power stroke?
ADP dissociates from the nucleotide binding site
This allows a new molecule of ATP to bind.
What is the sliding filament model?
A model of muscle contraction where actin and myosin slide over one another
This process uses chemical energy from ATP hydrolysis.
Define myoblast.
A large fused muscle cell containing many nuclei
Myoblasts share a common plasma membrane.
What is a myofibril?
A bundle of muscle fibers within a myoblast
Myofibrils are essential components of muscle tissue.
What is a sarcomere?
An overlapping arrangement of thick and thin filaments
Sarcomeres form a repeating structure in skeletal muscle.
What role does tropomyosin play in muscle contraction?
It is a thin filament protein that blocks myosin binding sites
Tropomyosin is arranged head-to-tail along actin polymers.
What is troponin?
A heterotrimeric protein complex that mediates Ca2⁺ regulation
Troponin plays a crucial role in muscle contraction regulation.
What is the function of titin in muscle fibers?
Acts as a flexible spring connecting myosin proteins to Z-disk proteins
Titin contributes to the elasticity of muscle fibers.
