A Tour of the Cell

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Actin filament

Myosin filament

Myosin arm

(a) Myosin motors in muscle cell contraction

Cortex (outer cytoplasm):

gel with actin network

Inner cytoplasm: sol

with actin subunits

Extending

pseudopodium

(b) Amoeboid movement

Nonmoving cortical

cytoplasm (gel)

Chloroplast

Streaming

cytoplasm

(sol)

Vacuole

Cell wall

Parallel actin

filaments

(c) Cytoplasmic streaming in plant cells

Slide 90

Fig, 6-27a

Muscle cell

Actin filament

Myosin filament

Myosin arm

(a) Myosin motors in muscle cell contraction

Slide 91

Fig. 6-27bc

Cortex (outer cytoplasm): gel with actin network

Inner cytoplasm: sol with actin subunits

Extending pseudopodium

(b) Amoeboid movement

Nonmoving cortical cytoplasm (gel)

Chloroplast

Cell wall

Streaming cytoplasm (sol)

Parallel actin filaments

(c) Cytoplasmic streaming in plant cells

Vacuole

Slide 92

Localized contraction brought about by actin and myosin also drives amoeboid movement

Pseudopodia (cellular extensions) extend and contract through the reversible assembly and contraction of actin subunits into microfilaments

Slide 93

Cytoplasmic streaming is a circular flow of cytoplasm within cells

This streaming speeds distribution of materials within the cell

In plant cells, actin-myosin interactions and sol-gel transformations drive cytoplasmic streaming

Video: Cytoplasmic Streaming

Slide 94

Intermediate Filaments

Intermediate filaments range in diameter from 8–12 nanometers, larger than microfilaments but smaller than microtubules

They support cell shape and fix organelles in place

Intermediate filaments are more permanent cytoskeleton fixtures than the other two classes

Slide 95

Concept 6.7: Extracellular components and connections between cells help coordinate cellular activities

Most cells synthesize and secrete materials that are external to the plasma membrane

These extracellular structures include:

Cell walls of plants

The extracellular matrix (ECM) of animal cells

Intercellular junctions

Slide 96

Cell Walls of Plants

The cell wall is an extracellular structure that distinguishes plant cells from animal cells

Prokaryotes, fungi, and some protists also have cell walls