Module 4 Section 1 Flashcards
Describe the distinctive features of the sarcomere as seen under a light microscope.
…
Describe the functions of the skeletal muscle contractile proteins.
Thick filaments
- Myosin = motor protein that uses ATP to move along actin filaments
Thin filaments
- Actin
- Tropomyosin
- Troponin
What type of neurotransmitter innervates the muscle at the neuromuscular junction?
ACh
Describe the various structures of the skeletal muscle.
1) Muscle: a whole skeletal muscle is made up of individual muscle fibres, each of which runs the entire length of the muscle.
2) Muscle fibre: they run parallel to each other and are surrounded by connective tissues. It’s actually a single muscle cell. These cells are multinucleated and have a very large number of mitochondria.
3) Myofibrils: along the length of a muscle fibre, the cell is divided into discrete contractile elements called myofibrils.
4) Myofibril (sideview): when viewed from the side using a light microscope, a myofibril displays a pattern of light and dark bands that give the muscle fibre a striated pattern, which is why skeletal muscle is sometimes called striated muscle.
5) Myofibril (cross section): you can see a highly organized cytoskeletal pattern of thick and thin filaments, which are myosin and actin, respectively.
Describe the 5 features of myofibrils.
A band
- Also called dark bands
- Made up of stacked thick and thin filaments that’re aligned parallel to each other and its borders are defined by the length of the thick filaments
- The middle of the A band is slightly lighter (H zone) since the thin filaments don’t reach this far from the ends
- The thin filaments (actin) = blue
- Thick filaments (myosin) = red
I band
- Also called the light bands
- Made up of the portion of the thin filaments that don’t extend into the A band
- In the middle of the I band is the Z line
- dArk = A band; LIght = I band
H zone
- Slightly lighter portion of the A band
- Only contains proteins that hold the thick filaments (myosin) together in a stack
- Myosin is composed of 2 heavy chains and 2 light ones
- It contines the heavy ones
M line
- The proteins that hold the thick filaments together in a stack
- It runs down the centre of the H zone
Z line
- In the middle of the I band is a vertical line called the Z line
- Sarcomere = the distance from one Z line to the next; it’s the functional unit of skeletal muscle
True or false: when relaxed, a sarcomere is about 2.5um in width
True
True or false: when muscles are growing, they extend the length of the muscle fibre by adding new sarcomeres onto the ends
True
What are cross-bridges?
It’s the connection formed when mobile myosin heads bind to actin molecules in muscles
Fill in the blanks:
The area in the ___ where the thick and thin filaments overlap contains ___, that extend from the ___ filaments and form when ___ filaments bind
The area in the A band where the thick and thin filaments overlap contains cross-bridges, that extend from the thick filaments and form when thin filaments bind
What are thick filaments composed of?
It’s composed of myosin which is a motor protein that uses ATP to move along actin filaments.
Describe the structure of myosin
- Each molecule of myosin is a dimer with 2 subunits. Each subunit looks like a golf club (long shaft and a globular head)
- When the dimers come together, the “shaft” portions wrap around together
- Within thick filaments, 2 dimers come together in a tail-to-tail formation and then these stack up w/ other myosin molecules
- The heads stick out and contain 2 important sites: an actin binding site and a myosin ATPase site
What are thin filaments composed of?
- They are made up of the proteins actin, propomyosin and troponin
- The main structural component is 2 actin filaments
What is actin?
Actin filaments are made up of individual spherical actin molecules that come together to form a double helix structure
What is tropomyosin?
Tropomyosin is a thin, double helix protein that lies end to end along the actin helix structure. It’s a regulatory protein that covers the active binding sites, preventing the interaction of actin and myosin
What is troponin?
Troponin is a regulatory protein complex made of 3 polypeptides. One binds to tropomyosin, one binds to actin and one binds to Ca
What is the correct order (from biggest to largest) for muscle fibre, myofibril and muscle?
Muscle -> muscle fibre -> myofibril
Label the sarcomere with the following:
- M line
- A band
- Z line
- H zone
- I band
---1--- --5-- 2 4 ------------------------------------- | | | | || | | | | | | | || | | | | | | | || | | | | | | | || | | | | | | | || | | | | -------------------------------------- --3--
1) A band
2) M line
3) H zone
4) Z line
5) I band
