Module 4: Lecture 2 Flashcards
True or False
Titin is the largest protein in the body
True
Titin contains how many amino acids?
27,000
What is the molecular weight of Titin?
3 million daltons
Which description of the sarcomere organization is correct?
a) The A- band contains no thin filaments
b) The H-zone contains no thin filaments
c) The z-discs are contained within the A-band
d) The I-band contains some thick filaments
B
How is your A-band defined?
based on the length of your thick filaments however there is an overlap of thin filaments as well
The Z-discs are contained in which band A or I?
I
What does your I-band contain?
it goes from one thick filament of one sarcomere to another thick filament of a second sarcomere
- z-line is included
What is the H-band
- From M-line to thick filaments where there is no overlap of thin filaments
- ONLY THICK FILAMENTS
True or False
Muscle contraction does not necessarily cause “shortening” of the muscle
True because of isometric contractions
What does the state of contraction refer to?
state in which your actin and myosin are forming cross bridges and generating force
What happens after a contraction of a muscle
relaxation of a muscle
True or False
The overlap for your thick and thin filaments in necessary for your cross-bridges to actually form
True
What is the signal that allows for the process of muscle contraction?
- the action potential from the neuromuscular junction
What molecule is the key that signals your actin and myosin cross-bridges to form?
increase in cytosolic calcium
What are your thin filaments made up of?
- quaternary structure (made up of multiple different protein chains)
- Globular actin
If we polymerize G-actin into a long chain we will form what?
- Filamentous actin
- aka F-actin
If we take 2 F-actin filaments and intertwine them what do we get?
Actin helix
How do we regulate the binding site on the actin filaments?
- tropomyosin
(regulatory protein) - they are intertwined on that actin helix physically blocking the binding site for myosin
What does troponin do?
regulates tropomyosin
- sensor about when the muscles is activated or not
What are the 2 key regulatory molecules that will allow muscles to contract or not?
- Troponin
- Tropomyosin
A single tropomyosin molecule can block how many actin molecules?
about 7 actin molecules
How many troponin molecules is needed to regulate a single tropomyosin
1
Troponin has 3 subunits which are what?
- T, Tropomyosin
- I, Inhibitory
- C, Calcium
What does the first subunit of troponin (T) do?
physically interacting with the tropomyosin molecule itself
- holding it in close proximity to the actual tropomyosin molecule
What does the second subunit of troponin (I) do?
keeps it in that inhibitory state and ensures that those binding sites are blocked
What does the third subunit of troponin (C) do?
responsible for sensing when a muscle contraction should be occurring
- calcium binds to troponin C and induces the conformational change, which removes inhibition
What is the thick filament made up of?
- lots of myosin molecules
A single myosin molecule is made up of what?
- 2 heavy chains
- 4 light chains
what does dimer mean?
composed of two heavy chains that are intertwined with their tail regions in this helical form
Within the head of a myosin molecule what are the 2 binding sites?
- Actin binding site
- binds to the thin filament to form the cross-bridge - ATP binding site
- where we hydrolyze ATP to perform a cross-bridge cycle
True or False
The myosin heads are coming out from both directions away from the M-line
True
One heavy chain contains what?
- 1 tail
- 1 head
What do light chain contain?
specialized protein that stabilize the head
(also a site for regulation)
- essential light chain
- regulatory light chain
One heavy chain has how many accompanying light chains?
2
What enzyme is also found at the ATP binding site?
ATPase
What are the 4 steps of the cross-bridge cycle?
- Binding between the myosin head and the thin filament
- Movement of the cross-bridges (Power stroke)
- Detachment of the cross-bridges: detach myosin from thin filament
- Re-energize the myosin head so it can re-attach to a thin filament repeating the cycle
What is a Power Stroke?
step in which the myosin head physically pulls the myofilament inwards towards the M-line
From rest to contracted sarcomere, what happens to the A-band, I-band, H-zone and overall sarcomere length?
A-band: no change
- pull thin filaments towards M-line
I-band: Shorten
- will decrease as the thin filaments are being pulled the thick filaments will get closer to the z-line
H-zone: Shorten
- as thin filaments come closer to M-line the H-zone will decrease as thin filaments overlap thick filaments
Sarcomere: Shorten
- Z-lines are getting closer to eachother
True or False
When we are contracting our thin and thick filaments will not actually change in length but their overlapping distances will be affected
True
