39 Questions
What is the primary role of intermediate filaments in cytoplasm?
Provides tensile strength
In smooth muscle cells, what triggers the phosphorylation of myosin II?
An increase in Ca2+ levels
During muscle contraction, what is the primary mechanism by which actin filaments interact with myosin filaments?
Actin filaments slide over myosin filaments
What is the primary function of motor proteins like dynein and kinesin?
Organizing microtubules
What is the primary trigger for muscle contraction in skeletal muscle cells?
A sudden rise in cytosolic Ca2+
What is the distance of head displacement along the filament during a power stroke in muscle contraction?
5 nm
What is the role of voltage-sensitive proteins in muscle contraction?
Regulation of calcium channels in the T-tubules
What is the result of the sudden rise in Ca2+ in muscle contraction?
Triggering of muscle contraction
What is the mechanism by which myosin molecules walk along actin filaments?
Through a cycle of structural changes
What is the role of the sarcoplasmic reticulum in muscle contraction?
Storage of calcium ions
What is the primary mechanism by which Ca2+ triggers muscle contraction?
Ca2+ binding to troponin, leading to movement of tropomyosin away from the myosin-binding site
What is the role of the sarcoplasmic reticulum in muscle contraction?
To store and release Ca2+ ions in response to electrical signals
How do myosin molecules move along actin filaments during muscle contraction?
Through a cycle of structural changes, using ATP hydrolysis to generate force
What is the role of tropomyosin in regulating muscle contraction?
To regulate the binding of myosin to actin filaments
What is the initial event that triggers muscle contraction?
Action potential spreading through the T-tubules
What is a characteristic feature of myosin II molecules?
It has two ATPase heads and a tail
What is the functional unit of contraction in a skeletal muscle cell?
Sarcomere
During muscle contraction, what is the movement of actin filaments relative to myosin filaments?
Actin filaments slide against myosin filaments
What is the organization of myosin II molecules in skeletal muscle cells?
They form clusters through their tails
What is the structure that makes up the bulk of the cytoplasm in a skeletal muscle cell?
Myofibrils
Microtubules are involved in the organization of which structure in the cytoplasm?
Cilia and flagella
What is the primary mechanism of motor protein movement?
Conformational change driven by ATP hydrolysis
What is the function of motor proteins like dynein and kinesin?
To transport different types of cargo along microtubules
What is the primary function of myosin motor proteins?
To drive contraction in muscle cells
What is the primary mechanism of microtubule dynamics?
Dynamic instability driven by GTP hydrolysis
What is the effect of actin monomer binding with ATP to ADP?
Reduces binding between monomers, thus decreasing polymer stability
What is the function of phalloidin?
Binds and stabilizes actin filaments
What is the characteristic of actin filaments in treadmilling?
The rates of addition and loss are equal
What is the function of cytochalasin?
Caps filament plus ends, preventing polymerization
What is the function of latrunculin?
Binds actin monomers and prevents their polymerization
What is the characteristic of actin filaments in eukaryotic cells?
They are thin and flexible
What is the role of actin filaments in animal cells?
They allow cells to migrate
What is the location of actin filaments in eukaryotic cells?
Underlying the plasma membrane
What is the similarity between actin and tubulin?
They polymerize by similar mechanisms
What is the characteristic of actin filaments in cell migration?
They are dynamic and flexible
What is the primary function of α-actinin molecules in the Z-disc?
To crosslink actin filaments from adjacent sarcomeres
During muscle contraction, what is the primary consequence of the sliding filament mechanism?
The sarcomere shortens without a change in filament length
What is the primary direction of myosin head movement during muscle contraction?
Toward the plus end of the adjacent actin filament
What is the primary requirement for muscle contraction to occur?
The presence of calcium ions
Study Notes
Muscle Contraction
- Muscle contraction is triggered by a sudden rise in cytosolic Ca2+.
- Action potential traverses T-tubules, triggering the release of Ca2+ from the sarcoplasmic reticulum.
- Ca2+ binds to troponin, causing tropomyosin to move away from the myosin-binding site, allowing myosin to bind and walk along the actin filament.
- Muscle contraction depends on the interaction of actin and myosin II.
Skeletal Muscle Contraction
- Skeletal muscle contraction is controlled by troponin and tropomyosin complexes.
- Ca2+ binding to troponin leads to the movement of tropomyosin, allowing myosin to bind to actin.
- Myosin II molecules have two ATPase heads and a tail, and they cluster together to form bundles.
Muscle Cells
- A skeletal muscle is a huge single cell formed by the fusion of many smaller cells.
- The bulk of the cytoplasm is made up of myofibrils, which are the contractile elements of the muscle cell.
- Each myofibril is made up of sarcomeres, which are assemblies of actin filaments and myosin II filaments.
Actin Filaments
- Actin filaments are thin and flexible, and they are essential for cell movements and changing cell shape.
- Actin filaments associate with different proteins to form structures that depend on the type of protein.
- Many proteins bind to actin and modify its properties.
- Actin filaments can undergo treadmilling, where the rates of addition and loss are equal, and the filament stays the same length.
Microtubules
- Microtubules are hollow tubes with structurally distinct ends.
- The centrosome is the major microtubule-organizing center in animal cells.
- Microtubules display dynamic instability, which is driven by GTP hydrolysis.
- Microtubules organize the cell interior, and motor proteins drive intracellular transport along them.
Motor Proteins
- Motor proteins, such as dynein and kinesin, move along microtubules and drive intracellular transport.
- Myosin is a motor protein that is involved in muscle contraction.
- ATP hydrolysis and phosphate release drive the movement of motor proteins.
Cytoskeleton
- The cytoskeleton is supported by cytoskeleton filaments, including intermediate filaments, microtubules, and actin filaments.
- Intermediate filaments provide tensile strength, microtubules organize organelles and move them, and actin filaments are involved in cell movement.
- The cytoskeleton plays a crucial role in maintaining cell shape and allowing cells to move.
Learn how muscle contraction occurs through the sliding filament mechanism, triggered by a sudden rise in calcium ions. Understand the role of myosin II and actin filaments in muscle contraction.
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