Chapter 48 Flashcards
How does dynein in cause movement in micro tubules?
Dynein is very large multimeric protein with MW exceeding 1,000,000 and is an ATPase
The splitting of ATP causes the dynein to change conformation and move individual micro tubules past one another
How is micro tubule composed?
Is composed of individual tublin components
Each of the tublin components is a dimer, composed of monomers of alpha-tublin and beta-tublin which are tightly associated
What are micro filaments?
In addition to micro tubules, cells also have microfilaments
-are formed by protein actine (ex: microvilli)
Microvilli are on the brush border cells of the small intestine
What is amoebic movement?
Actin with myosin can drive the movement of cells.
Occurs not only in the protozoan Amoeba but in many cells in the body
Contraction of actin and myosin pushes out the protrusions from the cell called pseudopods
Where else are actin and myosin found in the body?
Also found in muscle.
- cardiac muscle: cells electrically coupled, tightly joined to one another
- smooth muscle: cells arranged in sheets
- skeletal muscle: note striations
What causes myosin to change conformation?
Myosin filament consists of 6 molecules: 2 long coiled, alpha helic tails, and 4 smaller molecules that make 2 distinct heads at the end of tails. These heads have ATPase activity and the splitting of ATP provides the energy for a change in head conformation
How is action potential triggered in muscle?
Action potential releases ACh, this opens postsynaptic ACh channels in muscle membrane. Na+ flows into cell , muscle membrane depolarizes and triggers action potential down muscle
How do myosin and actin cause muscle movement?
1) action potential causes the release of Ca2+ from the SR and the Ca2+ binds to troponin. This causes a change in conformation if troponin and twisting of tropomyosin that leads to the exposing of myosin-binding sites on actin
2) the myosin head now attaches to the actin molecule
3) the Pi(HPO4-2) falls off the myosin get head and this part of the molecule undergoes a large change in conformation called the power stroke. The filaments slide past one another
4) ATP is hydrolyzed and myosin head returns to its resting position
5) now ATP binds to the myosin head in exchange for ADP, causing myosin to release from the actin
How does the sliding filament model or muscle contraction work?
Change in polarity is essential so that filaments slide pass one another on opposite directions on either side of the M band.
Thick filaments reverse polarity at the midline of sacromere, going opposite direction of the thin filaments
How does muscle attach to bone and bone attach to other bone?
Tendons attach muscle to bone
Ligaments attach bone to bone
Flexor and extensor muscle work antagonistically to operate the joint
Cartilage (between bones) is stiffer than tendons or ligaments because it is mostly collagen
What is the structure of collagen?
Consists of triple helix of 3 alpha-chains wrapped around one another. In each alpha-chain, every third amino acid is a glycine, the only amino acid small enough to occupy the crowded interior of the helix
What is ossification?
The process that turns cartilage (how bones begin) to bones.
Adds calcium phosphate to the cartilage to create hardened bone
Bones are storage centers for calcium in the body and are constantly remodeled during the life of the organism
What is the relation between osteoblasts and osteocytes?
In mature bone, the osteoclasts continue to burrow in the structure forming small cavities.
The osteoblasts the follow the osteoclasts and lay down new bone matrix
The interplay between osteoclasts and osteoblasts continually remodels the bone tissue
