Exam 4 - Lecture 7

Question 1

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

Answer 1

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

Question 2

The major structural
elements of the
cytoskeleton are

Answer 2

Microtubules
 Microfilaments
 Intermediate
filaments

Question 3

Microtubules are
composed of

Answer 3

tubulin
subunits and are about
25 nm in diameter

Question 4

Microfilaments subunits and size

Answer 4

7 nm
wide, are composed of
actin subunits

Question 5

Intermediate filaments
-size and composition

Answer 5

8–12 nm, are variable in
composition

Question 6

what is a Mechanically Integrated Structure

Answer 6

cytoskeleton

Question 7

MTs resist

Answer 7

bending when a cell is compressed

Question 8

MFs serve as

Answer 8

contractile elements that generate tension

Question 9

IFs are

Answer 9

elastic and can withstand tensile forces

Question 10

connect IFs, MFs, and MTs

Answer 10

linker proteins

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

Question 11

the largest structural
elements of the cytoskeleton

Answer 11

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

Question 12

what are the two main types of microtubules

Answer 12

Cytoplasmic microtubules

Axonemal microtubules

Question 13

Cytoplasmic microtubules

Answer 13

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

Question 14

Axonemal microtubules

Answer 14

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

Question 15

Describe the strucutre of MTs

Answer 15

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

Question 16

Describe Microtubule Assembly Graph

Answer 16

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.

Question 17

Describe the lag phase of MT assembly

Answer 17

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

Question 18

Drugs Affecting Cytoskeleton

Answer 18

Colchicine
Nocodazole

Question 19

Colchicine

Answer 19

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

Question 20

Nocodazole

Answer 20

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

Question 21

MTs originate from

Answer 21

a microtubule-organizing
center (MTOC)

Question 22

Many cells have an MTOC called a

Answer 22

centrosome near the nucleus

Question 23

In animal cells, the centrosome is associated
with

Answer 23

two centrioles surrounded by
pericentriolar material

Question 24

Centriole walls are formed by

Answer 24

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

Question 25

describe γ-Tubulin

Answer 25

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

Question 26

proteins promote depolarization of MTs

Answer 26

Stathmin/Op18 Catastrophins

Question 27

Microtubule Stability - MAPs

Answer 27

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

Question 28

Some MT-binding proteins use ATP to

Answer 28

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

Question 29

Stathmin/Op18

Answer 29

depolarizes MTs by binding to tubulin heterodimers and prevents their polymerization

Question 30

Catastrophins

Answer 30

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

Question 31

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

Answer 31

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

Question 32

What is actin? What are the various types?

Answer 32

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)

Question 33

actin assembly

Answer 33

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

Question 34

Drugs Affecting Microfilaments

Answer 34

Cytochalasins Latrunculin A

Question 35

Cytochalasins

Answer 35

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

Question 36

Latrunculin A

Answer 36

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

Question 37

Actin-Binding Proteins role + example

Answer 37

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

Question 38

Microvilli

Answer 38

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

Question 39

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

Answer 39

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

Question 40

what is unique about IF proteins

Answer 40

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

Question 41

6 classes of IFs

Answer 41

class 1 - 6

Question 42

describe class 1

Answer 42

Class I: acidic keratins

Question 43

describe class 2

Answer 43

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

Question 44

class 3

Answer 44

connective tissue, muscle cells, and glial cells

Question 45

class 4

Answer 45

nerve cells

Question 46

class 5

Answer 46

inner surface of the nuclear membrane

Question 47

class 6

Answer 47

nerve cells of embryos

Question 48

IF assembly

Answer 48

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

Question 49

Cell motility can be

Answer 49

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

Question 50

Contractility

Answer 50

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

Question 51

Two Eukaryotic Motility Systems

Answer 51

Microtubule-based motility Microfilament-based motility

Question 52

Microtubule-based motility example

Answer 52

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

Question 53

Microfilament-based motility example

Answer 53

Example: muscle contraction

Question 54

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

Answer 54

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

Question 55

Microtubule-associated motor proteins...

Answer 55

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

Question 56

Kinesin I

Answer 56

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

Question 57

Cytoplasmic dynein

Answer 57

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

Question 58

Kinesin Movement Along MTs

Answer 58

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

Question 59

ATP-dependent motors, the large superfamily called

Answer 59

myosins

Question 60

ATP-dependent motors =

Answer 60

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

Question 61

Myosin Functions

Answer 61

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

Question 62

Muscle contraction

Answer 62

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

Question 63

Mammals have what types of muscle

Answer 63

skeletal, cardiac, and smooth muscle

Question 64

Skeletal Muscle Cells contain what two filaments?

Answer 64

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

Question 65

Thick Filaments

Answer 65

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

Question 66

Thin Filamentsand the three proteins it contains

Answer 66

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

Question 67

The Sliding-Filament Model Explains Muscle Contraction

Answer 67

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

Question 68

give some functions of MTs, MFS, IF

Answer 68

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