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Cell Structure and Function > Exam 4 - Lecture 7 > Flashcards

Exam 4 - Lecture 7 Flashcards

1
Q

The cytoskeleton is a_______and plays a role in _______? Two features are_________.

A

network of
interconnected filaments and tubules
extending through the cytosol
 It plays roles in cell movement and division
 It is dynamic and changeable

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2
Q

The major structural
elements of the
cytoskeleton are

A

Microtubules
 Microfilaments
 Intermediate
filaments

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3
Q

Microtubules are
composed of

A

tubulin
subunits and are about
25 nm in diameter

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4
Q

Microfilaments subunits and size

A

7 nm
wide, are composed of
actin subunits

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5
Q

Intermediate filaments
-size and composition

A

8–12 nm, are variable in
composition

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6
Q

what is a Mechanically Integrated Structure

A

cytoskeleton

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7
Q

MTs resist

A

bending when a cell is compressed

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8
Q

MFs serve as

A

contractile elements that generate tension

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9
Q

IFs are

A

elastic and can withstand tensile forces

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10
Q

connect IFs, MFs, and MTs

A

linker proteins

Example: plectin, found at sites
where intermediate filaments connect to Mts and MTF

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11
Q

the largest structural
elements of the cytoskeleton

A

Microtubules (MTs)
 They are involved in a variety of functions in the
cell

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12
Q

what are the two main types of microtubules

A

Cytoplasmic microtubules

Axonemal microtubules

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13
Q

Cytoplasmic microtubules

A

pervade the cytosol and
are responsible for a variety of functions:
 Formation of mitotic and meiotic spindles
 Maintaining or altering cell shape
 Placement and movement of vesicles

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14
Q

Axonemal microtubules

A

Axonemal microtubules include the organized and
stable microtubules found in structures such as Cilia
and Flagella

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15
Q

Describe the strucutre of MTs

A

MTs are straight, hollow cylinders of varied length that consist of
longitudinal arrays of polymers called protofilaments
 The basic subunit of a protofilament is a heterodimer of tubulin, one
α-tubulin and one β-tubulin
 These bind non-covalently to form an αβ-heterodimer, which does
not normally dissociate
 Microtubules can form as Singlets, Doublets, or Triplets

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16
Q

Describe Microtubule Assembly Graph

A

MT formation is slow at first
because the process of
nucleation is slow; this period
is known as the lag phase
 The elongation phase is
much faster
 Plateau phase: the mass of
MTs reaches a point where the
amount of free tubulin is
diminished.

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17
Q

Describe the lag phase of MT assembly

A

MT formation is slow at first
because the process of
nucleation is slow; this period
is known as the lag phase

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18
Q

Drugs Affecting Cytoskeleton

A

Colchicine
Nocodazole

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19
Q

Colchicine

A

binds to tubulin monomers, inhibiting their assembly into MTs
and promoting MT disassembly
 Vinblastine, vincristine are related compounds

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20
Q

Nocodazole

A

inhibits MT assembly, and its effects are more easily reversed
than those of colchicine

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21
Q

MTs originate from

A

a microtubule-organizing
center (MTOC)

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22
Q

Many cells have an MTOC called a

A

centrosome near the nucleus

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23
Q

In animal cells, the centrosome is associated
with

A

two centrioles surrounded by
pericentriolar material

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24
Q

Centriole walls are formed by

A

9 pairs of triplet
microtubules
 oriented at right angles to each other
 involved in basal body formation for cilia and flagella
 cells without centrioles have poorly organized mitotic
spindles

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25
Q

describe γ-Tubulin

A

Centrosomes have large
ring-shaped protein
complexes in them; these
contain γ-tubulin
 γ-tubulin is found only in
centrosomes

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26
Q

proteins promote depolarization of MTs

A

Stathmin/Op18
Catastrophins

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27
Q

Microtubule Stability - MAPs

A

Cells regulate MTs with great precision
 Others regulate MT structure
 MAPs, microtubule-associated proteins, bind along a
microtubule wall, allowing for interaction with other cellular
structures and filaments

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28
Q

Some MT-binding proteins use ATP to

A

to drive vesicle or
organelle transport or to generate sliding forces between MTs

29
Q

Stathmin/Op18

A

depolarizes MTs by binding to tubulin heterodimers and prevents
their polymerization

30
Q

Catastrophins

A

depolarizes Mts by acting at the ends of MTs and promote the
peeling of subunits from the ends

31
Q

Microfilaments
1. size
2. best known role
3. 3 main involvements

A

are the smallest of the
cytoskeletal filaments
 Best known for their role in muscle
contraction
 Involved in cell migration, amoeboid
movement, and cytoplasmic streaming

32
Q

What is actin?
What are the various types?

A

the Protein Building Block of Microfilamens

Actin is a very abundant protein in all
eukaryotic cells
 Actins can be broadly divided into
muscle-specific actins (α-actins) and
nonmuscle actins (β- and
γ-actins)

33
Q

actin assembly

A

Once synthesized, it folds into
a globular-shaped molecule
that can bind ATP or ADP (G-
actin; globular actin)
 G-actin molecules polymerize
to form microfilaments: F-actin
 All the actin monomers in the
filament have the same
orientation

34
Q

Drugs Affecting Microfilaments

A

Cytochalasins
Latrunculin A

35
Q

Cytochalasins

A

are fungal metabolites that prevent
the addition of new monomers to existing MFs

36
Q

Latrunculin A

A

is a toxin that sequesters actin
monomers and prevents their addition to MFs

37
Q

Actin-Binding Proteins role + example

A

Actin-binding proteins: used
by cells to precisely control
where actin assembles and
the structure of the resulting
network
 Example: Capping
proteins bind the ends of a
filament to prevent further
loss or addition of subunits

38
Q

Microvilli

A

Actin bundles in microvilli
are the best-studied
examples of ordered actin
structures
 Microvilli are prominent
features of intestinal
mucosal cells; they increase
the surface area of the cells
 The core of a microvillus
consists of a tight bundle of
MFs with the ends pointed
toward the tip

39
Q

Intermediate filaments (IFs)
where are they found?
Common example
stability and solubility?
important function

A

are not
found in cytosol of plant cells but are
abundant in many animal cells
 An IF is keratin, an important
component of structures that grow from
skin in animals
 IFs are the most stable and least soluble
components of the cytoskeleton
 They likely support the entire
cytoskeleton

40
Q

what is unique about IF proteins

A

IF Proteins Are Tissue Specific
IFs differ greatly in amino acid composition from tissue to tissue

41
Q

6 classes of IFs

A

class 1 - 6

42
Q

describe class 1

A

Class I: acidic keratins

43
Q

describe class 2

A

Class II: basic or neutral keratins
* Proteins of classes I and II make up the keratins found in epithelial
surfaces covering the body and lining its cavities

44
Q

class 3

A

connective tissue, muscle cells, and glial cells

45
Q

class 4

A

nerve cells

46
Q

class 5

A

inner surface of the nuclear membrane

47
Q

class 6

A

nerve cells of embryos

48
Q

IF assembly

A

The fundamental subunits of
IF proteins are dimers
 IF proteins are fibrous rather
than globular
 Each has a homologous
central rodlike domain
 Flanking the central helical
domain are N- and C-
terminal domains that differ
greatly among IF proteins
IFs Assembly
 Two IF polypeptides
intertwined into a coiled-coil
 Two dimers align laterally to
form a tetrameric protofilament
 Protofilaments overlap to build
up a filamentous structure
about eight protofilaments thick

49
Q

Cell motility can be

A

Movement of a cell or organism through the
environment
 Movement of the environment past or through a
cell
 Movement of components in the cel

50
Q

Contractility

A

used to describe shortening of
muscle cells, is a specialized form of motility

51
Q

Two Eukaryotic Motility Systems

A

Microtubule-based
motility
Microfilament-based
motility

52
Q

Microtubule-based
motility example

A

examples: fast axonal transport
in neurons; the sliding of MTs in
cilia and flagella

53
Q

Microfilament-based
motility example

A

Example: muscle contraction

54
Q

Microtubule-Based Movement Inside Cell requires what two proteins and whaat is the role of MT

A

Kinesins and Dyneins
MTs provide a rigid set of tracks for transport of a variety of
organelles and vesicles

55
Q

Microtubule-associated motor proteins…

A

Microtubule-associated motor proteins—kinesins and
dyneins—walk along the MTs and provide the force needed for
movemen

56
Q

Kinesin I

A

is involved in ATP-dependent transport
toward the plus ends (away from the centrosome),
called anterograde axonal transport

57
Q

Cytoplasmic dynein

A

moves particles (cargo) in the
opposite direction, called retrograde axonal transport

58
Q

Kinesin Movement Along MTs

A

Kinesin movement looks like “walking,”
with the two globular head domains
taking turns as the front foot
 It can move long distances along an MT
before detaching from it by releasing
bound ADP and acquiring a new ATP,
so that the cycle repeats

59
Q

ATP-dependent motors,
the large superfamily
called

A

myosins

60
Q

ATP-dependent motors =

A

myosins
the large superfamily
myosins, interact
with and exert force on
actin microfilaments
 Currently there are 24
known classes of myosins

61
Q

Myosin Functions

A

Myosins function in a wide range of cellular events,
including
 Muscle contraction
 Cell movement
 Phagocytosis
 Vesicle transport

62
Q

Muscle contraction

A

is the most familiar example of mechanical
work mediated by intracellular filaments

63
Q

Mammals have what types of muscle

A

skeletal, cardiac, and smooth muscle

64
Q

Skeletal Muscle Cells contain what two filaments?

A

muscle fibers contain thin
filaments containing actin
and thick filaments
containing myosin

65
Q

Thick Filaments

A

Each thick filament consists of
hundreds of molecules of myosin,
oriented in opposite directions in
the two halves of the filament
 The myosin is arranged in
staggered fashion
 Protruding heads of myosin
molecules contact the adjacent
thin filaments, forming cross-bridges

66
Q

Thin Filamentsand the three proteins it contains

A

Thin filaments interdigitate (interlock) with the thick
filaments
 Thin filaments contain three proteins: F-actin,
intertwined with tropomyosin and troponin

67
Q

The Sliding-Filament Model Explains Muscle
Contraction

A

The sliding filament model was proposed in 1954
 According to the model, muscle contraction is due to thin
filaments sliding past thick filaments, with no change in length
of either

68
Q

give some functions of MTs, MFS, IF

A

MT ( varies per type, but Axonemal = cell motility, and cytosoolic varies)

MF - muscle contractions, cell locomotion, cyoplasmic steaming, cell shape, intracellulat transport

IF - structural support, animal cell shape, stregth of nerve cell axons

Cell Structure and Function (8 decks)

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