A Tour of the Cell

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10

Slide 81

Fig. 6-24

0.1 µm

Triplet

(c) Cross section of basal body

(a)

Longitudinal section of cilium

0.5 µm

Plasma membrane

Basal body

Microtubules

(b)

Cross section of cilium

Plasma membrane

Outer microtubule doublet

Dynein proteins

Central microtubule

Radial spoke

Protein cross-linking outer doublets

0.1 µm

Slide 82

How dynein “walking” moves flagella and cilia:

Dynein arms alternately grab, move, and release the outer microtubules

Protein cross-links limit sliding

Forces exerted by dynein arms cause doublets to curve, bending the cilium or flagellum

Slide 83

Fig. 6-25

Microtubule

doublets

Dynein

protein

ATP

ATP

(a) Effect of unrestrained dynein movement

Cross-linking proteins

inside outer doublets

Anchorage

in cell

(b) Effect of cross-linking proteins

1

3

2

(c) Wavelike motion

Slide 84

Fig. 6-25a

Microtubule doublets

Dynein protein

(a) Effect of unrestrained dynein movement

ATP

Slide 85

Fig. 6-25b

Cross-linking proteins inside outer doublets

Anchorage in cell

ATP

(b) Effect of cross-linking proteins

(c) Wavelike motion

1

3

2

Slide 86

Microfilaments (Actin Filaments)

Microfilaments are solid rods about 7 nm in diameter, built as a twisted double chain of actin subunits

The structural role of microfilaments is to bear tension, resisting pulling forces within the cell

They form a 3-D network called the cortex just inside the plasma membrane to help support the cell’s shape

Bundles of microfilaments make up the core of microvilli of intestinal cells

Slide 87

Fig. 6-26

Microvillus

Plasma membrane

Microfilaments (actin filaments)

Intermediate filaments

0.25 µm

Slide 88

Microfilaments that function in cellular motility contain the protein myosin in addition to actin

In muscle cells, thousands of actin filaments are arranged parallel to one another

Thicker filaments composed of myosin interdigitate with the thinner actin fibers

Slide 89

Fig. 6-27

Muscle cell