M2 L2 Flashcards
Each unit from one z-disc to another is made up of what? How are they placed?
Made up of sarcomeres. They are placed in series along the myofbril
Looking at the internal structure of a sarcomere, what do you see?
Each sarcomere contains myofilaments (responsible for generating force). They can be either thin or thick filaments
Thick filaments:
* whats the length
* whats the diameter
* what made of
* whats their orientation to the force trajectory
- 1.6 micrometer length
- 11 nm in diameter
- made of myosin (300 myosin heavy chain (MHC) and 600 myosin light chain (MLC))
- parallel to force trajectory
Thin filaments:
* whats the length
* whats the diameter
* what made of
- 1.0 micromemeter
- 5 nm in diameter
- G-actin (primary constituent) at 350 and other regulatory girls like troponin and tropomyosin (50 and 50)
Label sarcomere regions. Which parts shorten?
I-band shortens and H-band
2 hypothesis about how muscles shorten + stretch
- Filament shortening: during contract thin filaments shorten (pull z-disc together)
- sliding filament theory: the thin filaments slide past the thick filaments and dont shorten which pulls the Z-discs closer together and shortens only the sarcomere.
How do muscles adapt?
By increasing sarcomere length by adding more sarcomeres at the end of myofibrils
Looking at the length tension curve, discuss the points 1.6, 2.0, 2.2, and 3.6
1.6: at lengths less than 2, thin filaments will start to collide together which takes more energy to push them together which means less force. the thick filaments also hit z discs
2.0: thin filaments run into each other but still possible to generate good force
2.2: this is the optimal length and has the most force because of a lot of thin/thick filament overlap
3.6: too stretched = no force. this happens bc thick filament is 1.6 the the 1.0 - they add up to 3.6 so once you pull apart fully they can’t overlap and they need to overlap to produce force.
What are cross-bridges?
Structures that pass between thick and thin filaments that increase force
How do the thin and thick filaments work together to produce force
The thin filament contains G-actin, along with regulatory proteins troponin and tropomyosin that control binding. The thick filament is made of myosin, with myosin heads that stick out and reach toward the thin filament.
Then, when contraction starts:
* Calcium binds to troponin, shifting tropomyosin and exposing binding sites on actin.
* Myosin heads attach to actin, forming cross-bridges.
What is the arrangement of a thin filament? List the components and their actions
made up of an alpha helix that contains 7 G-actin. Each actin subunit has a binding site for myosin.
- contains tropomyosin which wraps around actin, blocking myosin-binding sites in a resting muscle.
- Also has Troponin that’s attached to tropomyosin and has three parts (covered later)
What is the arrangement of a thick filament? List the components and their actions
The tails of myosin bind together and the heads stick out on opposite sides facing outwards.
Each myosin molecule has:
* MHC which forms the myosin head and tail.
* MLC which is small proteins that attach to the myosin head, helping regulate movement and force.
The tails of MHC join at the M (when sideways)
What now determines how force much can be generated?
How well the heads of myosin molecules are able to interact with thin filaments. More interactions mean more cross bridge formation
What is a cross bridge
cross-bridge is the temporary connection between a myosin head (on the thick filament) and actin (on the thin filament) during muscle contraction.
What enables force production?
An increase in Ca2+ in muscle and energy (ATP present) will cause a change in orientation of the myosin head (from rest) and they will make contact with the thin filaments
what is the cross bridge cycle
The cross-bridge cycle is the repeated process by which myosin heads bind to actin, generate force, and detach, driving muscle contraction. It is regulated by Ca2+
