Effectors I

How do actin, tropomyosin and troponin work together?

Actin has binding sites for myosin attachment but they are blocked by strands of tropomyosin at rest. This tropomyosin strand will only be moved when troponin is activated by the binding of Calcium ions to troponin. It's moved because the calcium binding to the protein troponin causes a conformation change that moved the whole troponin tropomyosin complex. Now the actin can bind to the myosin attachment

Cardiac muscle

found only in the heart, striated , involuntary; pacemaker cells and intercalacated disks

Z discs/lines

structures at the end of sarcomeres that the actin filaments get anchored to; one sarcomere is the space between two Z lines

Pacemaker cells

that spontaneously initiate cardiac muscle contraction

Which stays the same length and which changes: actin filament, myosin filament and the sarcomere?

The sarcomere gets smaller as the filaments slide past each other but stay the same length

Do the thin or thick filaments move?

The thin filaments get pulled by the thick filaments. The thick stay in place (kind of)

How are flagella/cilia structured?

They have a 9+2 microtubule pattern, meaning that there are 9 pairs of microtubules in a ring and two in the middle. The pairs are connected via protein bridges and dyneins which generate the force to make it move

Muscle shortening is caused by (A) Movement of myosin motor proteins along actin filaments (B) Movement of actin motor proteins along myosin filaments (C) Shortening of actin filaments along myosin filaments (D) Shortening of myosin filaments along actin filaments (E) Combined shortening of myosin and actin filaments (F) Combined movement of myosin and actin filaments

A

Cilia, flagella, and muscle activity are all dependent upon (A) ATP (B) Motor proteins (C) Actin (D) Myosin (E) Tropomyosin (F) Neural stimulation

A and B

Which of the following statements correctly describe(s) T tubules and their role in conducting action potentials in muscle cells? All that apply (A) Without T tubules, the muscle cell would not be able to contract. (B) tubules have receptor proteins that bind neurotransmitters released from the synaptic terminal of the motor neuron. (C) tubules carry action potentials throughout the muscle cell

A and C T-tubules are specialized structures that propagate the action potential throughout the muscle cell, causing release of calcium from the sarcoplasmic reticulum. because calcium is required for muscle contraction, muscles would not be able to contract in the absence of functional T-tubules. receptors for neurotransmitters are located at the synapse between the neuron and muscle cell (the neuromuscular junction). binding of neurotransmitters to these receptors causes localized membrane depolarization in the muscle cell (fiber), when is the propagated throughout the muscle cell via the T-tubules.

What are three essential things for movement in muscles?

ATP, motor proteins, and actin microfilaments

What are three essential things for movement of cilia and flagella?

ATP, dynein motor proteins, and microtubule tracks

Describe the process of moving the troponin-tropomyosin complex from neural beginning to end

An action potential is sent down an efferent neuron which releases the neurotransmitter acetycholine into the synaptic cleft and binds to receptors on the muscle cell. This depolarizes it and sends out another action potential in the muscle. The action potential goes from T tubules to the SR. Depolarization of the SR causes the release of calcium. The calcium will bind to the troponin, causing the whole complex to shift and expose myosin binding sites on the actin filament. At the end of the action potential, calcium is rapidly pumped back into the SR.

Muscle contraction is controlled by (A) Movement of actin motor proteins along myosin filaments (B) Movement of myosin motor proteins along actin filaments (C) Shortening of actin filaments along myosin filaments (D) Shortening of myosin filaments along actin filaments

B

What is the role of tropomyosin in muscle contraction? (A) has binding site for motor protein head (B) protein that controls access to myosin-binding sites (C) filament that pulls the other filament towards the center of the sarcomere

B

Which of the following statements correctly describe(s) the relationship between Ca2+ concentration in the cytosol and the response in the sarcomere? (A) Increasing Ca2+ concentration causes troponin and tropomyosin to bind to actin. (B) Increasing Ca2+ concentration causes movement of tropomyosin, exposing myosin-binding sites on actin. (C) Decreasing Ca2+ concentration promotes interactions between actin and myosin.

B

What is the role of the actin (thin) filament in muscle contraction? All that apply (A) filament that pulls the other filament towards the center of the sarcomere (B) filament that is pulled towards the center of the sarcomere (C) binding sites for motor protein head (D) has motor protein heads that hydrolyze ATP

B and C the actin filament is the filament that is pulled toward the center of the sarcomere by myosin; actin which has binding sites for the myosin motor protein heads; the myosin filament has ATP-drivin motor protein heads that pull the actin filament toward the center of the sarcomere to cause contraction.

Smooth muscle differs from skeletal muscle as (A) Smooth muscle lacks troponin-tropomyosin complexes but does have myosin (B) Smooth muscle lacks the myosin and actin filaments present in skeletal muscle (C) Smooth muscle does not contract following neural stimulation unlike skeletal muscle (D) Smooth muscle has actin and myosin filaments but they are not organized like skeletal muscle (E) Smooth muscle contains more myoglobin than skeletal muscle and can thus sustain contractions for far longer

D

The calcium ions released into the cytosol during excitation of skeletal muscle bind to (A) actin (B) tropomyosin (C) myosin (D) troponin

D

Skeletal muscle

Voluntary muscle which is attached to bones or skin and controlled locomotion. They are long and cylindrical and striated. Multiple nuclei per one cell

What are the three components of the thin filaments in sarcomeres?

actin, tropomyosin and troponin

What does kinesin do and where is it?

associated with tubulin microtubules and is required for movement of vesicles and other intracellular cargoes

What does dynein do and where is it?

associated with tubulin microtubules and required for movement of cilia and flagella

Microfilaments (actin filaments)

double helix structure composed of actin protein subunits. They serve as tracks for motor protein myosin

What does myosin do and where is it?

it's associated with actin microfilaments and is required for movement of a muscle

Myofibrils

long cylindrical structures that run the entire length of a muscle fiber; contain many sarcomeres

Microtubules

made up of tubulin proteins arranged to form a follow, straw-like tub that serves as tracks for motor protiens kinesin and dyenin. important to cellular structural integrity and cell movement

Explain the cross bridge cycle

myosin binds to ATP, myosin hydrolyzes ATP into ADP and an inorganic phosphate and remains bound to both, if the tropomyosin-troponin complex has moved and exposed the myosin binding site (which is on the ACTIN filament) the myosin will bind there. After this binding, the myosin releases the inorganic phosphate and stays bound to the ADP molecule. The release of the inorganic phosphate molecule causes a powerstroke, which pulls the actin filament towards the M line. After this the ADP is released, the myosin will remain stuck to the actin filament until it can bind with another ATP molecule and start over

Smooth muscle

occurs in walls of hollow organs and tracts. Not under voluntary control, no striations

sarcoplasmic reticulum (SR)

the endoplasmic reticulum of a muscle cell that stores calcium

Sarcomeres

the functional groups that cause the contraction of a muscle; they give the muscle the striated appearance due to the alteration of actin and myosin. Myosin forms the thick dark bands and actin is the thin light bands

Motor Proteins

the proteins required to interact with cytoskeleton for cell motility; there are three types: myosin, dynein and kinesin

intercalated disks

which enable rapid passage of action potentials from one cardiac muscle cell to the next.