sliding filament

• The width of the H zone _______ during a contraction and _______ during relaxation.

Decreases, increases

Where is myosin found in skeletal muscle cells? a. in the thin filaments b. in the thick filaments c. in the sarcoplasmic reticulum d. in the terminal cisternae e. in the T tubules

b. thick filaments

What happens after the tropomyosin moves over, exposing the binding sites on the actin?

cross bridge can happen

During relaxation, the myosin heads _______ and the ____________.

detach from the actin, thin filaments slide back to their resting position

what happens during step 1 of the cross bridge

Presence of an action potential in the muscle cell membrane. Release of calcium ions from the terminal cisternae. Calcium ions rush into the cytosol and bind to the troponin. There is a change in the conformation of the troponin-tropomyosin complex. This tropomyosin slides over, exposing the binding sites on actin

Many or little power strokes occur to bring the Z lines of the sarcomere closer together during the contraction of a muscle cell.

many

During the contraction of a sarcomere about half of the ________ and about_______ . If all the myosin heads detached at the same time, then ________

myosin heads are attached to actin,half are bound at any given time,the thin filament would slide back on the thick filament.

If these six steps occurred exactly as shown in the animation, the sarcomere would.....? so what happens due to this?

not move very far - it would only shorten about 1%. In the contraction of a typical sarcomere, step 1 occurs then steps 2-5 repeat themselves over and over again, before step 6 occurs. This allows the thin filament to slide all the way inward. Steps 2-5 repeat themselves over and over as long as both ATP and calcium ions are present.

Two binding sites of myosin

one of top of the head for actin an one under the head for ATP

• The length of the sarcomere _____ during a contraction, but the thin and thick filaments do or do not shorten, they just ________.

shortens, do not, they just slide by each other

What causes the myosin binding sites on actin to be exposed?

the calcium ions that cause the chang ein conformation of troponin and tropomyosin

What happens during step 2 of cross bridge

the hinge on the tail of the myosin bending and the energized myosin head binding into the actin. Note during this entire step, the myosin head is in its high energy, upright position. If it was tilted backward, in its low energy position, the actin binding site would not be in the proper position to bind the actin.

What does it mean when the terminal cisternae and the sarcoplasmic reticulum are continuous

the pumping of calcium ions back into the sarcoplasmic reticulum causes an increase in calcium ions within the terminal cisternae as well. This animation shows the calcium ions being pumped back into the terminal cisternae, but they are really pumped back in along the length of the sarcoplasmic reticulum.

where is myosin found

thick filaments

According to the sliding filament theory, when a muscle cell contracts, the __________ filaments slide past the ___________ filaments and the ____________ shortens.

thin filaments thick and the sacromere

When a muscle cell contracts, the ____ slide past the _____ and the ________ .

thin filaments,thick filaments,sarcomere shortens

Thin filaments are made of these three protein molecules:

1. actin 2. tropomyosin 3. troponin

whats the cycle of the myosin head

1.ATP binds to myosin heads when they are tilted back in their low energy position. When ATP is hydrolyzed into ADP and phosphate, the energy is released and transferred to the myosin head.(cross bridge) 2. the tail hinges and allowing the mysoin to come into contact with actin 3. the ADP and Pi are released from the head, and the head tilst back to create the power stroke. cross bridge goes from high energy to low energy 4. myosin head is now in low energy conformation 5. to repeat process, ATP binds to head but does not transfer the energy to the head yet

What happens during step 4 of cross bridge

ATP binding to the myosin head, allowing the myosin head to disconnect from the actin. Note that even though the ATP has bound, the energy has not yet been transferred from the ATP to the cross bridge since the head is still tilted backward.

What happens during step 5 of cross bridge

ATP is hydrolyzed into ADP and phosphate. The energy (yellow glow) is transferred from the ATP to the myosin head, which points upward

What three protein molecules are the thin filaments made of?

Actin 3. Tropomyosin 4. Troponin

Muscle Contraction summary:

Action Potential Occurs -> Calcium Ions are Released from the Terminal Cisternae -> Calcium Ions then Bind to Troponin -> Tropomyosin Moves Away from the Myosin Binding Sites on Actin

What happens during step 6 of cross bridge

Calcium ions fall off the troponin. Calcium is taken back up into the sarcoplasmic reticulum. Tropomyosin covers the binding sites on actin

What is actin

The major component of the thin filament, actin is composed of a double strand of actin subunits each of which contain myosin binding sites.

What is tropomyosin

The regulatory protein, tropomyosin, is also part of the thin filament. Tropomyosin twists around the actin. When the sarcomere is not shortening, the position of the tropomyosin covers the binding sites on the actin subunits and prevents myosin head binding.

Review of bidns to what Participant 1. Myosin 2. Actin 3. Tropomyosin 4. Troponin 5. ATP 6. Calcium ions

Will bind to: 1.ATP, Actin 2.Myosin, Troponin 3.Troponin 4.Calcium, Tropomyosin, Actin 5.myosin 6. tropnin

List the six most important chemicals involved in muscle contraction

1. Myosin 2. Actin 3. Tropomyosin 4. Troponin 5. ATP 6. Calcium ions

parts of mysoin and what they do

Myosin has a tail and two heads and binding site, which will move back and forth, providing the power stroke for muscle contraction. • The tail of myosin has a hinge which allows vertical movement so that the myosin head can bind to actin. The myosin head has a binding site for ATP.

What causes the release of calcium ions into the cytosol from the terminal cisternae?

The action potential, which is the electrical signal consisting of the depolarization and subsequent re-polarization of a nerve or muscle which travels along the membrane and functions as a signal to initiate an activity

6 basic steps of cross bridge cycle

Step 1: Exposure of Binding Sites on Actin Step 2: Binding of Myosin to Actin Step 3: Power Stroke of the Cross Bridge Step 4: Disconnecting the Myosin Head Step 5: Re-energizing the Myosin Head Step 6 Removal of Calcium Ions

what happens during step 3 of the cross bridge

The ADP and Pi are released from the actin. The myosin head tilts backward. The power stroke occurs as the thin filament is pulled inward toward the center of the sarcomere. -There has been a transfer of energy from the myosin head to the movement of the thin filament.

What is troponin

Troponin, which is found periodically along the tropomyosin strand, functions to move the tropomyosin aside, exposing the myosin binding sites.