Muscle Contraction Flashcards
What is the optimum length of the sarcomere?
2.25 um
What happens when a sarcomere is too long or short?
Too short and myosinruns into z disks, too long and myosin cannot reach the actin filaments.
What is the z disk made out of?
CapZ and alpha-actinin
Which end of the actin anchors to the z disk
the barbed (plus) end
What does tropomodulin do?
It caps the - end of the actin filaments, in the sarcomere
Nebulin:
Is the same length as the actin filament. It is a moleculer ruler
Titan:
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.
Compare the half life of actin subunits in the sarcomere to those without
several days in sarcomere
minutes outside a sarcomere
What are the steps of myosin in muscle contraction?
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
What does tropomyosin do?
It blocks the binding site for myosin
How does tropomyosin relate to troponin C?
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.
What are the three proteins of troponin and their function.
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+
Sarcoplasmic reticulum relates to muscle contraction how?
It stores the Ca2+ needed for contraction.
What are T tubules?
What are transverse T tubules?
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.
Electro-Mechanical coupling of action potential the L-type Ca2+ channel refers to what?
The mechanism and process of converting an action potential into the opening of L-type Ca2+ channel in the SR
abut means:
come into very close contact with.
What is the purpose of having SR wrapped T tubule associated myofibrils?
We have cut down the diffusion distance that Ca2+ has to travel in order to make it the center of the myofibril.
I band:
A band:
I band: The actin
A band: The myosin
Triads:
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)
What are ryanodine receptors?
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
What are L-type cav1.1 channels?
They are voltage gated calcium channels which reside in t-tubules. Four of these channels bind mechanically to each Ryanodine receptor (RYR1).
How many cav1.1 proteins make contact with a RyR1 tetramer?
4
RyRs does what?
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.
L type Cav1.1 is also known as the
Dihydropyridine receptor (DHPR) because it binds dihydropyridine-class drugs used to treat hypertension and heart failure.
Is extracellular Ca2+ necessary for skeletal muscles to fire?
Is extracellular Ca2+ necessary for cardiac muscles to fire?
No
Yes
What brings Ca2+ back into the cell?
Ca2+ ATPases (ca2+ pumps), aka SERCA (sarcoplasmic-Endoplasmic Reticulum Ca2+ ATPases.
Serca’s run
Constantly
What is resting Ca2+ levels?
100 nM
What is excitatory Ca2+ levels?
10-100uM
A point mutation in Arg403 –> Gln403 causes what?
Heart enlargement and death
Cardiac muscle cells are connected by _______
located at _______.
GAP JUNCTIONS
INTERCALATED DISCS.
What is a a gap junction composed of?
- 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
Connexons have sulfur linkages in the extracellular space, why do these not exist in the cytoplasm?
The pH is lower in the cytoplasm so….
S-S –> S-H + H-S
RyR2 is present where?
Ryanodine receptor two is present in cardiac muscle cells.
Is Ca2+ influx required for the heart E-C coupling of cardiac cells?
Yes
Cav1.2 is present where?
Cav1.2 is a L-type channel, that is located in the cardiac muscle.
Smooth muscle cells are ______ and ______.
spindle-shape
mononucleated.
The inner layer of smooth muscle is ______.
The outer layer of smooth muscle is ______.
circular
longitudinal
Both are used in peristalsis
What is different about myosin arrangement in smooth cells?
Myosin is arranged in a grid/lattice connected by dense bodies. Causes the cell to ‘shrink’ when contracted
In smooth muscle
Most of the Ca2+ needed comes from ______. So there is less ______.
Extracellular space
SR
Explain the steps of smooth muscle contraction.
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.
Where does myosin light chain kinase phosphorylate?
The light chain of Myosin II.
How do G protein coupled receptors play into smooth muscle contraction?
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
What is a bipolar arrangement of myosin?
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.
Are myosin filaments longer in skeletal or smooth muscle?
Skeletal muscle.
