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Cell biology > Muscle Contraction > Flashcards

Muscle Contraction Flashcards

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1
Q

What is the optimum length of the sarcomere?

A

2.25 um

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2
Q

What happens when a sarcomere is too long or short?

A

Too short and myosinruns into z disks, too long and myosin cannot reach the actin filaments.

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3
Q

What is the z disk made out of?

A

CapZ and alpha-actinin

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4
Q

Which end of the actin anchors to the z disk

A

the barbed (plus) end

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5
Q

What does tropomodulin do?

A

It caps the - end of the actin filaments, in the sarcomere

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6
Q

Nebulin:

A

Is the same length as the actin filament. It is a moleculer ruler

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7
Q

Titan:

A

Is a massive molecular spring (~1 um). It is thought to be a molecular ruler to determine the length of the overall sarcomere (two titan’s in length)
It is believed to act as a spring which pulls the myosin back to the actin filaments if they get disconnected.

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8
Q

Compare the half life of actin subunits in the sarcomere to those without

A

several days in sarcomere

minutes outside a sarcomere

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9
Q

What are the steps of myosin in muscle contraction?

A

1) Attached: Starts attached, bound in the rigor formation (already having pulled on actin)
- binding of ATP to nucleotide binding site
2) Released: makes it release
- ATP –> ADP + Pi both ADP and the Phosphate are still attached to myosin.
3) Cocked: This cocks myosin.
- Pi is removed from myosin
4) Force Generating: Myosin grabs actin
- ADP is detached (the power stroke)
5) Attached

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10
Q

What does tropomyosin do?

A

It blocks the binding site for myosin

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11
Q

How does tropomyosin relate to troponin C?

A

Troponin C is related to calmodulin. In the presence of Ca2+ it pulls on troponin T to cause tropomyosin to shift, exposing myosin’s binding site.

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12
Q

What are the three proteins of troponin and their function.

A

Troponin I: binds to Actin filament
Troponin C: Ca2+ binding site, transfers its conformational change to troponin T.
Troponin T: Shifts tropomyosin out of the way once troponin C binds Ca2+

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13
Q

Sarcoplasmic reticulum relates to muscle contraction how?

A

It stores the Ca2+ needed for contraction.

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14
Q

What are T tubules?

What are transverse T tubules?

A

T tubules: are invaginations of the plasma membrane

transverse T tubules: Are T tubules which run around myofibrils in close proximity to the TERMINAL CISTERNAE of the SR. They are transferring the signal to the SR.

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15
Q

Electro-Mechanical coupling of action potential the L-type Ca2+ channel refers to what?

A

The mechanism and process of converting an action potential into the opening of L-type Ca2+ channel in the SR

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16
Q

abut means:

A

come into very close contact with.

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17
Q

What is the purpose of having SR wrapped T tubule associated myofibrils?

A

We have cut down the diffusion distance that Ca2+ has to travel in order to make it the center of the myofibril.

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18
Q

I band:

A band:

A

I band: The actin

A band: The myosin

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19
Q

Triads:

A

Triad:

  • Consists of T tubules and the terminal cisternea of the SR.
  • Is the site of Electro-Mechanical coupled signaling (for cardiac and skeletal muscles)
20
Q

What are ryanodine receptors?

A

They are calcium channels with a tetromer within the cytosol. Each monomer of the tetromer is gated to L-type Cav1.1 channel (which reside in the ER). when these channels open it opens the Ryanodine receptors and releases Ca2+ into the cell

21
Q

What are L-type cav1.1 channels?

A

They are voltage gated calcium channels which reside in t-tubules. Four of these channels bind mechanically to each Ryanodine receptor (RYR1).

22
Q

How many cav1.1 proteins make contact with a RyR1 tetramer?

A

4

23
Q

RyRs does what?

A

It is a receptor for ryanodine (a plant alkaloid) that has been modified RYR1 receptor types seen in muscle, or both came from a common ancestor.

24
Q

L type Cav1.1 is also known as the

A

Dihydropyridine receptor (DHPR) because it binds dihydropyridine-class drugs used to treat hypertension and heart failure.

25
Q

Is extracellular Ca2+ necessary for skeletal muscles to fire?
Is extracellular Ca2+ necessary for cardiac muscles to fire?

A

No

Yes

26
Q

What brings Ca2+ back into the cell?

A

Ca2+ ATPases (ca2+ pumps), aka SERCA (sarcoplasmic-Endoplasmic Reticulum Ca2+ ATPases.

27
Q

Serca’s run

A

Constantly

28
Q

What is resting Ca2+ levels?

A

100 nM

29
Q

What is excitatory Ca2+ levels?

A

10-100uM

30
Q

A point mutation in Arg403 –> Gln403 causes what?

A

Heart enlargement and death

31
Q

Cardiac muscle cells are connected by _______

located at _______.

A

GAP JUNCTIONS

INTERCALATED DISCS.

32
Q

What is a a gap junction composed of?

A
  • A transmembrane channels called connexon.
  • They seem to have 6 subunits. - A connexon is cell1 is connected to a connexon in cell2.
  • they can open and close
33
Q

Connexons have sulfur linkages in the extracellular space, why do these not exist in the cytoplasm?

A

The pH is lower in the cytoplasm so….

S-S –> S-H + H-S

34
Q

RyR2 is present where?

A

Ryanodine receptor two is present in cardiac muscle cells.

35
Q

Is Ca2+ influx required for the heart E-C coupling of cardiac cells?

A

Yes

36
Q

Cav1.2 is present where?

A

Cav1.2 is a L-type channel, that is located in the cardiac muscle.

37
Q

Smooth muscle cells are ______ and ______.

A

spindle-shape

mononucleated.

38
Q

The inner layer of smooth muscle is ______.

The outer layer of smooth muscle is ______.

A

circular
longitudinal

Both are used in peristalsis

39
Q

What is different about myosin arrangement in smooth cells?

A

Myosin is arranged in a grid/lattice connected by dense bodies. Causes the cell to ‘shrink’ when contracted

40
Q

In smooth muscle

Most of the Ca2+ needed comes from ______. So there is less ______.

A

Extracellular space

SR

41
Q

Explain the steps of smooth muscle contraction.

A

1) extracellular ca2+ floods the cells
2) Calmodulin activates myosin light chain kinase (MLCK)
3) MLCK phosphorylates myson heads (cross bridges) causing contraction
4) myosin phosphatase dephosphorylates myosin, triggering
relaxation.

42
Q

Where does myosin light chain kinase phosphorylate?

A

The light chain of Myosin II.

43
Q

How do G protein coupled receptors play into smooth muscle contraction?

A

I ligand binds to GPCR. This in turn causes Ca2+ release from SR (likely IP3 2nd messenger), which activates calmodulin, which activates MLCK, which phosphorylates

44
Q

What is a bipolar arrangement of myosin?

A

An arrangement in which the filaments on one side pull a different direction then the filaments on the other side. The arrangement that is seen in really all sarcomeres.

45
Q

Are myosin filaments longer in skeletal or smooth muscle?

A

Skeletal muscle.

Cell biology (27 decks)

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