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bmsc 220 > Lecture #7 > Flashcards

Lecture #7 Flashcards

1
Q

The cytoskeleton is composed of three filamentous structures: ?

A

Microtubules (MT)
Intermediate filaments (IFs)
Actin filaments (F-actin or microfilaments)

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2
Q

________ _________: Strong, flexible, ropelike fibers (10 – 12 nm in dia) that provide mechanical strength to cells that are subjected to physical stress (neurons, muscle, epithelial)

A

Intermediate Filaments

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3
Q

Intermediate Filaments are chemically _________ group of structures (70 different genes)

A

heterogeneous

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4
Q

Intermediate filaments are divided into five major classes:
4 classes are ______
1 is associated with the _____ ______ (Lamins)

A

cytoplasmic, nuclear envelope

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5
Q

Intermediate filaments are often interconnected to other cytoskeletal filaments by thin, wispy cross-bridges consisting of a dimeric protein called ______.

A

plectin

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6
Q

Each _____ dimer has a binding site for an IF at one end and a binding site for another intermediate filament, F-actin, or microtubule at the other end

A

plectin

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7
Q

Common Intermediate Filament architecture:
1. Each monomer has a ____ of globular terminal domains separated by a long fibrous alpha-helical region (polar)
2. Pairs of _________ are associated in parallel orientation to form dimers (polar)
3. Dimers associate in an anti-______, staggered fashion to form tetramers (none polar)
4. 8 _______ associate to form a unit length of the IF (none polar)
5. These unit lengths associate with one another in an end-to-end fashion to form the _______ intermediate filament (none polar)

A

pair, monomers, parallel, tetramers, elongated

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8
Q

Unlike microtubules and F-actin, none of the assembly steps of IFs require the direct involvement of either ____ or ____. Once assembled, the subunits are not incorporated at one end of the filament but into the filament’s _______.

A

ATP, GTP, interior

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9
Q

Unlike the other two major cytoskeletal elements, assembly and disassembly of IFs are controlled primarily by subunit phosphorylation and ____________.

A

dephosphorylation

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10
Q

________ containing IFs – structural proteins of epithelial cells

A

Keratin

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11
Q

IF radiate through the ______, tethered to the nuclear envelope in the _____ of the cell, and anchored at the outer edge of the cell by desmosomes and hemidesmosomes. IFs are also connected to microtubules and F-actin. They function to organize and maintain cellular _______ and absorb mechanical _____

A

cytoplasm, center, architecture, stress

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12
Q

___________ (NFs) – Bundles of IFs are located in the cytoplasm of mature neurons – oriented parallel to the axon

A

Neurofilaments

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13
Q

___________ of NFs is seen in several human neurodegenerative disorders such as Parkinson’s disease. These NF aggregates may block axonal transport on microtubules leading to neurons _______

A

Aggregation, death

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14
Q

______ filaments (F-actin, microfilament) are the third major type of cytoskeletal element that is involved in intracellular motility

A

Actin

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15
Q

__-_____ is a flexible, helical filament composed of actin monomers (the most abundant protein in most cells) and is a two-stranded structure with two ______ grooves running along its length.

A

F-actin, helical

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16
Q

Actin filaments help determine: ?

A

Cell shape
Intracellular mobility of organelles (vesicles)
Cell motility (growing axon)

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17
Q

Depending on their activity, actin filaments can be organized into: ?

A

ordered arrays
highly branched networks
tightly anchored bundles

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18
Q

All actin monomers within an actin filament are pointed in the ____ direction, resulting in a _____ filament with so-called “barbed” or (+) end and “pointed” or (-) end.

A

same, polar

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19
Q

Actin protein is
- A major contractile muscle ______
- A major protein in every _______ cell

A

protein, eukaryotic

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20
Q

Before it is incorporated into a filament, an _____ monomer binds an ATP molecule

A

actin

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21
Q

_____ is an ATPase, just as ________ is a GTPase

A

Actin, tubulinβ

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22
Q

The _____ nucleation event in filament formation occurs slowly in vitro, whereas the subsequent stage of filament elongation occurs much more ______. (just like microtubules

A

initial, rapidly

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23
Q

Both ends of a filament become labeled, but the fast-growing ______ end incorporates the monomers at a rate about 10 times that of the _______ end

A

barbed, pointed

24
Q

Actin assembly/disassembly in vitro:
1. Preformed _____ filaments (seed) are added in the presence of ATP-actin
2. As long as the concentration of ATP-actin monomers remain _____, subunits are added to both ends
3. As ATP-actin monomers are consumed by addition to the ends of the filaments the concentration of free ATP-actin drops, until a point is reached where net addition of monomers continues at the ______ end but stops at the _______ end
4. As filament elongation continues, the free monomer concentration _____, such that monomers continue to be added to the ______ (+) ends of the filaments, but a net loss of subunits occurs at their _______ (-) end.
5. A point is reached where the two reactions at opposite ends of the filaments are balanced, such that both the lengths of the filaments (assembly = disassembly) and the concentration of free monomers remain constant, this leads to F-actin moving in the direction of assembly, known as “________.”

A

actin, high, barbed, pointed, drops, barbed, pointed, treadmilling

25
Q

By controlling this dynamic behavior, the cell can rapidly reorganize its actin cytoskeleton, required for dynamic processes such as: ?

A

cell locomotion
changes in cell shape
phagocytosis
cytokinesis

26
Q

Myosins are generally divided into two broad groups: ?

A

Conventional (or type II): muscle cells
Unconventional: most other cells

27
Q

______ function as molecular motors that operate in conjunction with actin filaments

A

Myosins

28
Q

Myosins move toward the _______ (+) end of an actin filament (with one exception)

A

barbed

29
Q

All Myosins share a characteristic _____ (head) domain

A

motor

30
Q

The head domain of myosins contains two sites: ?

A

a site that binds an actin filament
a site that binds and hydrolyzes ATP to drive the myosin motor

31
Q

Whereas the head domains of various myosins are similar, the _____ domains are highly divergent

A

tail

32
Q

__________ myosins: Primary motors for muscle contraction, but are also found in a variety in nonmuscle cells

A

Conventional (Type II)

33
Q

Among their nonmuscle activities, type II myosins are required for: ?

A

splitting a cell in two during cell division
generating tension at focal adhesions
cell migration

34
Q

Myosin II consists of:
1. a pair of ______ heads that contain the catalytic site of the molecule (binds to ATP)
2. a pair of necks, each consisting of a single, uninterrupted α _____ and two associated ____ chains
3. a single, long, rod-shaped ____ formed by the intertwining of long α-helical sections of the two ______ chains.

A

globular, helix, light, tail, heavy

35
Q

The fibrous tail portion of myosin II plays a structural role so it can form _______

A

filaments

36
Q

Myosin II molecules assemble so that the ends of the tails point toward the _____ of the filament and the globular heads point _____ from the center. As a result, the filament is _____, indicating a reversal of polarity at the filament’s center.

A

center, away, bipolar

37
Q

Because they are bipolar, the myosin heads at the opposite ends of a myosin filament have the ability to pull actin filaments ______ one another

A

toward

38
Q

Myosin II filaments can assemble ________ when and where they are needed

A

transiently

39
Q

Myosin ___ moves processively in a hand-over-hand fashion similar to that of the kinesin and dynein, so at least one of the _____ heads must be bound to its polarized track at all times

A

V, two

40
Q

Several ________ myosins (including myosin I, V, and VI) transport various types of cytoplasmic vesicles and organelles

A

unconventional

41
Q

A skeletal muscle fiber is a ________ cell. Each muscle fiber contains hundreds of cylindrical strands called __________. Each myofibril consists of a repeating linear array of contractile units called ________.

A

multinucleate, myofibrils, sarcomeres

42
Q

A _________ extends from one Z line to the next Z line and has a densely staining M line that lies in the center of the H zone

A

sarcomere

43
Q

The I band contains only _____ filaments. The H zone contains only _____ filaments. The part of the A band on either side of the H zone represents the region of ______ and contains both types of filaments.

A

thin, thick, overlap

44
Q

_________ of sarcomeres results from the thin and thick filaments sliding over one another

A

Shortening

45
Q

As a sarcomere shortens:
The __ band remains constant in length. The __ band and __ bands decrease in width and then disappears altogether. The __ lines on both ends of the sarcomere move inward until they contact the outer edges of the __ band.

A

A, H, I, Z, A

46
Q

Thin filaments of a skeletal muscle contain _____, ________, and ______

A

actin, tropomyosin, troponin

47
Q

_________ is an elongated molecule (approximately 40 nm long) that fits securely into the grooves within the thin filament and is associated with seven actin subunits

A

Tropomyosin

48
Q

_______ is a globular protein complex composed of three subunits, spaced about 40 nm apart along the thin filament, and contact both actin and tropomyosin

A

Troponin

49
Q

Actin filaments of each half sarcomere are aligned, with barbed ends linked to the __ line

A

Z

50
Q

During a contraction:
Each myosin head extends outward and binds tightly to a ____ filament, forming across-bridge between the two types of filaments. When bound to the _____ filament, myosin head undergoes a conformational change that moves the thin actin filament towards the sarcomere _____. Since each thin filament is contacted by a team of a hundred or so myosin heads that beat out of synchrony with one another; it undergoes _________ motion during each contractile cycle.

A

thin, actin, center, continuous

51
Q

The organization and behavior of actin filaments inside cells are determined by the interaction of actin with a variety of actin-binding _______

A

proteins

52
Q

Actin-binding proteins can be divided into categories based on their presumed function in the cell: (8 possibilities) ?

A

Nucleating
Monomer-sequestering
End-blocking (capping)
Monomer-polymerizing
Actin filament depolymerizing
Cross-linking and bundling
Filament-severing
Membrane-binding

53
Q

Cell locomotion is required for many activities in higher vertebrates, including: ?

A

tissue and organ development
formation of blood vessels
development of axons
wound healing
spread of cancerous tumors

54
Q

Cell locomotion, as exhibited by the ________, shares properties with other types of locomotion. As it moves, it flattens itself close to the substratum and becomes fan-shaped, with a broadened _____ end and a narrow “tail.”

A

fibroblast, frontal

55
Q

Fibroblast locomotion is seen by examining its ______ edge, it is extended out from the cell as a broad, flattened, veil-like protrusion and is called a ________

A

leading, lamellipodium

56
Q

As a lamellipodium is extended from the cell, it adheres to the underlying substratum at _______ points (focal adhesions), providing temporary _____ sites for the cell to pull itself forward

A

specific, anchor

bmsc 220 (22 decks)

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