ZO 250 Exam II Chapter 6

Cytoskeleton

Cytoskeleton

Used for movement inside the cells 3 ways: road for motor protein carriers, reorganize the cytoskeletal network, motor proteins pull on the cytoskeletal rope

Microtubules

"roads" that motor proteins dynein and kinesin can transport subcellular component, hollow, hydrolysis of ATP fueled. They are polar, (-) and (+) end. When anchored on (-) end, does not degrade.

Microfilaments

Composed of actin. They are "roadways" for the motor protein myosin. The movement arises from actin polymerization and sliding filaments.

Kinesin

move in (+) beta direction toward membrane

Dynesin

moves in (-) direction, toward MTOC (microtubule organizing center), larger and faster than kinesin

Alpha

(-), disassembly

Beta

(+), assembly

Microtubule

Made of tubulin, larger than microfilaments

Microfilament

made of actin, double stranded, linked together by filamin when in tangled networks and by fascin when they are in bundles

Motor Protein Movement

Movement through actin polymerization and sliding filament model

ATP binds on mysosin head, detaches from actin, ATP is hydrolyzed, myosin head reattaches to actin, energy from hydrolysis converted to power stroke, phosphate released and actin moves, ADP is released, actin and myosin remain attached.

Microtubule Associated Proteins (MAPS)

proteins that anchor MTs to the cell membrane and to each other.

MTOC

also like the nucleus- is instructs the movement of things inside and out along the pathways and initiates formation of a MT.

Cilia

numerous and cause a wavelike motion, composed of microtubules arranged into axoneme (bundle of parallel microtubules).  asymmetric activation of dynein causes the moveme

Flagella

are single or in pairs and cause a whiplike motion, composed of microtubules arranged into axoneme (bundle of parallel microtubules). the combination of dynein and the MTs cause the whipping motion.

Treadmilling

when assembly and disassembly occur at the same time and the overall length of the MF is constant.

Microtubules in cytokinesis

ensure that chromosomes are equally divided.

Microtubules in axon structure

support the long axons

Microtubules in vesicle transport

carry hormones and neurohormones from sites of synthesis to sites of release

Microtubules in pigment dispersion

control the distribution of pigment granules throughout the cell to affect animal color

Filapodia

roadlike extensions of the cell membrane. They are used to connect nerve cells and increase the surface area of the small intestine (microvilli).

Lamellapodia

sheetlike extensions of the cell membrane. They allow cells to crawl by rapid assembly and disassembly of actin and how this pushes regions of the membrane outwards. (Leukocytes, macrophages, cancer cells)

Actin in sperm

battering ram, The actin rods grow and push through the jelly coat of the egg (lipid layer) and then disassemble so that the sperm DNA can be transferred into the egg.

Fascin

cross-link microfilaments when bundled

Filamin

link microfilaments together when they are tangled

Dystrophin

used when microfilaments are linked to the membrane

Myosin

actins motor protein partner, ATPase, head is where ATPase activity takes place/interacts, neck regulates the activity, tail binds to subcellular components (cargo binds here)

Duty Cycle

how long the myosin is attached to the actin. It is the cross-bridge time/cross-bridge cycle time (and is usually 0.5).

Unitary Displacement

the distance myosin steps during each cross-bridge cycle. It depends on the myosin neck length and location of the binding site on actin. how many actin forward has the myosin head moved.

Sliding Filament Model

like pulling yourself along a rope.

• In the chemical reaction, myosin binds to actin (cross-bridge).

• In the structural change, myosin bends (Powerstroke).

What happens in the sliding filament model if there is no ATP

ATP is needed to release and reattach to actin. Without ATP. myosin cannot bind to actin and rigor mortis occurs.

SFM Cross Bridge Cycle

the formation of the cross-bridge, the power stroke, the release, and then extension.

Steps of the sliding filament model

1. ATP is available, binds to binding site on head of myosin, which then detaches from actin. (ATP binds causing myosin to detach).

2. ATP is hydrolyzed, myosin head extends forward and reattaches to actin. (Myosin head extends and attaches to adjacent actin).

3. Energy produced from hydrolysis is converted into power stroke as P is removed - actin moves! (Release of phosphate promotes power stroke).

4. ADP is released, actin and myosin remain attached. (ADP is released).

Both MF and MTs

vesicle transport

Actin and Myosin in Biological Systems

 vesicle transport, microvilli, amoeboid movement, skeletal muscle contractions, cardiac muscle contractions, and smooth muscle contractions.

Parts of the Sarcomere

the z-disk, the a-band, the i-band, nebulin, and titin.

Z Disc

forms border of each sarcomere

Thin filaments are attached to it and extend from it towards the middle of the sarcomere

 a-band (anisotropic band)

the middle region of the sarcomere occupied by thick filaments (actin).

 i-bands (isotropic bands)

• are located on either side of the z-disk.

• They are occupied by thin filaments.

Nebulin

along the length of the thin filaments.

Titin

keeps the thick filaments centered and attaches the thick filaments to the z-disk

Sarcomere

the basic unit of a striated muscle cell.

Myocyte

 a type of muscle cell.

Thin Filaments

 are attached and extend towards the middle of the z disk, nebulin along the length MYOSIN

Thick Filaments

centered and attached to the z disk by titin ACTIN

Troponin

a small unit attached to tropomyosin made of 3 subunits: TnC, TnI, and TnT.

TnC

the Ca sensor

TnI

inhibitor that binds to actin and blocks myosin from binding.

TnT

interacts with tropomyosin to block several binding sites.

Tropomyosin

the "rope" that is over the actin binding sites making it so that myosin cannot bind.

Ca2+ in Contractions

triggers contraction by reaction with regulatory proteins that in the absence of calcium prevent interaction of actin and myosin.

Muscle Fibers

contain many myofibrils and contract by means of the sliding filament mechanism like skeletal muscle.

Cardiac Muscle Fibers

are shorter and interconnected which makes coordinate contractions possible without having individual innervation.

EC Coupling

regulates muscle contractions by depolarizing the muscle plasma membrane (sarcolemma), elevating intracellular Ca2+, and then a contraction happens (sliding filament model).

Sarcolemma

the muscle plasma membrane.

Sarcoplasmic Reticulum

 stores Ca2+ that is bound to protein sequestrin and has terminal cisternae that increase storage.

T-tubules (transverse tubules)

invaginations of the sarcolemma, enhance the penetration of an AP into the myocyte, and are more developed in larger and faster twitching muscles and less developed in cardiac muscles.

SR in cardiac muscles

have well-developed terminal cisternae in birds and mammals, but are poorly developed in lower vertebrates.

SR in skeletal muscles

the amount of terminal cisternae depends on the fiber type

Myogenic

beginning in muscles, spontaneous (ex. heart), f/funny channels,

Neurogenic

beginning in the nerve, excited by neurotransmitters from motor neurons (ex. skeletal muscles)

Pacemaker Cells

cells that depolarize the fastest and have an unstable resting potential.

Ca2+ Controlled to Regulate Contraction

AP is conducted down the sarcolemma to the t-tubules. Depolarization opens DHDR (a protein in the cell surface) wich causes Ca2+ to enter from the extracellular fluid.

• In the cardiac muscle, high Ca2+ causes RyR (a protein on the SR) to open and release Ca2+ from the stores.

  • This is called Ca2+ induced Ca2+ release.

• In skeletal muscles, change in DHDR shape causes RyR to open and release Ca2+.

  • This is called depolarization induced Ca2+ release.

Smooth Muscles

no sarcomeres/striations, thick and thin filaments scattered, no t-tubules, minimal SR, connected by gap junctions

Billfish Heater Eye

have specialized muscle cells w few myofibrils and abundant SR and mitochondria

• Futile cycle of Ca2+ in/out of SR

• High rate of ATP synthesis/consumption

• Muscle contraction is used to just generate heat