Chapter 17

Front 1

The plasma membrane of eukaryotic cells is supported by

Back 1

actin filaments

Front 2

Actin-binding proteins that generate actin filament bundles

Back 2

are short and inflexible

Front 3

Decoration of actin filaments with myosin S1 is commonly used to

Back 3

reveal the polarity of actin filaments

Front 4

Many actin cross-linking proteins contain

Back 4

a CH-domain.

Front 5

Within an actin filament, each actin subunit is surrounded by _______ neighboring actin subunits

Back 5

Four

Front 6

Which region of myosin interacts with actin filaments?

Back 6

the head domain

Front 7

What propertie is not shared by all myosins?

Back 7

The ability to form dimers.

Front 8

All myosins move towart the (+) end of actin filaments except

Back 8

myosin VI.

Front 9

In the operational model for movement of myosin along an actin filament, the power stroke occurs during

Back 9

release of phosphate (Pi)

Front 10

What is the function of CapZ and tropomodulin in the sacromere?

Back 10

to maintain a constant actin thin filament length

Front 11

Vesicle transport along actin filaments is driven by

Back 11

myosin I

Front 12

Multinucleated cells may result from a defect in

Back 12

myosin II

Front 13

How do actin filaments appear when viewed by negative stain electron microscopy?

Back 13

When viewed by negative-stain electron microscopy, an actin filament appears as a twisted string of beads with a diameter of 7–9 nm.

Front 14

What cellular components cause some actin filaments to form bundles and others to form networks?

Back 14

Different types of actin-binding proteins cause some actin filaments to form bundles and others to form networks. All have two actin-binding sites, and the proteins that promote bundle formation tend to be short and inflexible, whereas the proteins that promote network formation tend to be longer and more flexible.

Front 15

Describe the functional properties of the head, neck, and tail domains of myosin

Back 15

The head domain of myosin is a specialized ATPase that couples the hydrolysis of ATP with motion. The activity of the myosin-ATPase is activated by binding to actin. The neck is an -helical region that is critical for converting small conformational changes in the head domain into large movements of the molecule and for regulating the activity of the head domain. The tail domain contains the binding sites for other molecules such as the thick filament in muscle.

Front 16

What are the functions of the myosin head domain and tail domain, respectively?

Back 16

The myosin head domain is the portion of the motor protein that binds actin filaments and uses the energy of ATP hydrolysis to generate movement along the filament. All types of myosins have similar head domains. The myosin tail domain acts to recognize and bind cellular cargo. Each type of myosin has a different tail domain and thus can potentially move a different kind of cargo (although myosin II forms a bipolar filament).

Front 17

What contractile structure is essential for cell division?

Back 17

The contractile ring is a transient contractile bundle formed toward the end of mitosis. It is laterally attached to the cell membrane, and as the ring contracts, the plasma membrane is brought together between the spindle poles until the membrane fuses and two new cells are created.