L4 - Skeletal Muscle Contraction (Chapters 6-7) Flashcards
Be able to label this diagram
Myofiber
- elongated muscle cell
- size is due to fusion of myoblasts
- many nuclei along the periphery
Myofibril
- filament like structure that contains the contractile components actin and myosin
- component of myofibers
Sarcolemma
plasma membrane of muscle cells
Sarcoplasm
cytoplasm of muscle cells
Sarcoplasmic reticulum
modified smooth endoplasmic reticulum, storage site for intracellular calcium
What other specializations to skeletal muscle cells possess?
- many mitochondria (muscle need a lot of ATP to function)
- glycosomes - cellular inclusion (molecules that form large complexes)
- myoglobin - carries O2 (similar to hemoglobin, but can only carry 1 or 2 molecules of oxygen)
- SR/T tubule system
Be able to label the structure of a myofibril
What is a sarcomere?
- basic contractile unit of myofibrils
- cause of striated appearance in skeletal and cardiac muscle
What are the parts of a sarcomere?
- Z discs border the sarcomere
- M line goes down the center of each sarcomere
- H zone surrounds the M line
- A band is isotropic
- I band is anisotropic
What proteins are found in each part of the sarcomere? Which regions contain actin, which contain myosin, and which contain both? Can you draw a myofibril in cross-section? How many actin filaments surround each myosin filament?
- thick filaments are made of myosin (motor protein)
- thin filaments are made of actin
- I band is made of actin
- A band is made of both actin and myosin
- H zone only has myosin
What is the structure of the myosin filaments? Can you draw one?
- a.k.a. thick filaments
- 6 total peptides - 2 heavy chains and 4 light chains
What are the two major parts of myosin filaments? Which part contains the actin binding site? Which part contains the ATPase?
- Head - composed of 2 light chains and a heavy chain
- Tail - contains two heavy chains wound helically around each other
- Head contains both the actin binding site and ATPase
What is the purpose of the actin binding site and ATPase located in/on the head of myosin?
- ATPase breaks down ATP, allows for phosphate via hydrolyzing to be freed and used to power functions
- actin binding sites are for binding actin… duh
What are myosin crossbridges?
- the arm and head of myosin that interact with each other during contraction
- involved in the walk-along theory of contraction (ratcheting motion of head towards arm after binding to actin pulls the actin along)
What are the hinges of myosin crossbridges? What is their function?
- extends away from myosin tail in the form of a hinge
- connection point btwn head and arm of crossbridge
- allows for dynamic action like a ratcheting motion
What is the structure of the actin filaments? Can you draw one?
also called thin filaments
F-actin
- filamentous component of actin
- found of microtubules
- polymer of G-actin
G-actin
- globular component of actin
- reserve pool of actin used to make microtubules
- contains binding sites for myosin, tropomyosin and troponin
How are G-actin and F-actin related?
G-actin is the monomer of F-actin, and F-actin is the polymer of G-actin
Where are the myosin binding sites located? How are they arranged along F-actin?
- located on G-actin
- offset to point out radially from F-actin helix
What two other proteins associate with F-actin in sarcomeres? How are these proteins arranged along F-actin?
- Troponin is located on top of tropomyosin
- Tropomyosin is located on the myosin binding sites
What is the function of troponin and tropomyosin on actin filaments?
- Tropomyosin blocks the binding of myosin to actin bc it has a higher affinity for myosin binding sites – imp for when muscle is relaxed, there is no binding
- Troponin moves tropomyosin out of the way when muscle needs to contract so that myosin can bind to actin
Titin
- also called connectin
- largest know protein
- extends from Z disc to M line
- more likely to collect mutations bc the gene sequence of this protein is large
- present in striated muscle only
What does a mutation of titin cause?
- dilating cardiomyopathy - dilation of ventricles that can result in an overall weakening of the myocardium
- can also cause skeletal myopathies