CHAPTER 2
Cell Structure and Function
13
characteristic of the basal surfaces of epithelia, but they are not
restricted to epithelia. Examples of other cells with basal lami-
nae are muscle cells and the Schwann cells that enshroud the
axons of peripheral nerves.
Cytoskeleton (Fig. 2-1)
Actin
f
laments
: These are thin (6 nm) F laments that form a
feltwork (cortex) beneath the plasmalemma of many cells. They
form a skeletal core of microvilli, and they also function in the
movement of motile cells. In contractile cells, actin F
laments
interact with myosin (thick) F laments.
Intermediate
f
laments
: These are relatively stable 10-nm to
12-nm F laments that provide structural support for the cell.
Different speciF
c proteins that form these F laments are charac-
teristic of particular groups of cell types.
Microtubules
: These are hollow tubes about 25 nm in diameter.
In conjunction with other proteins, particularly kinesin and
dynein, they serve as tracks for movement of materials within
the cytoplasm. Microtubules also form centrioles and the basal
bodies and axonemes (cores) of cilia.
Centrosome
: This is composed of a pair of centrioles embedded
in amorphous material. The two centrioles are oriented at right
angles to each other, and each is composed of nine triplet sets of
microtubules. The centrosome functions in organizing the array
of microtubules in the cell’s cytoplasm and in
developing the
spindle apparatus during cell division.
SYNOPSIS 2-1
Functions of Major Cell Components
Nucleus
Nucleus
:
Synthesizes all types of RNA; replicates its DNA.
Heterochromatin
:
Condenses inactive DNA.
Euchromatin
:
Renders DNA accessible to transcription.
Nucleolus
:
Produces ribosomal RNA; assembles ribosome particles.
Nuclear envelope
:
Segregates DNA from cytoplasmic constituents.
Nuclear pore
:
Controls access of molecules that move between the nucleus and the cytoplasm.
Cell Surface
Microvillus
:
Increases the area of plasmalemma at a free (apical) surface of an epithelial cell.
Basal or basolateral Fold
:
Increases the area of plasmalemma at the basolateral surface of an epithelial cell.
Cilium
:
Moves the material along the apical surface of an epithelial cell.
Basal lamina
:
Contributes to the boundary between a cell and its surrounding interstitium.
Cytoskeleton
Actin f
lament
:
Contributes to contraction, cell motility, and cell stiffness.
Myosin f
lament
:
Interacts with actin to produce contraction.
Intermediate f
lament
:
Contributes to structural (mechanical) strength of a cell
.
Microtubule
:
Provides tracks for intracellular movement of molecules and particles; generates movement of cilia and
movement of chromosomes during cell division.
Cytoplasm
Mitochondria
:
Generate ATP and contribute to synthesis of some molecules.
Ribosome
:
Translates mRNA to polypeptides.
Rough endoplasmic reticulum
(
RER
)
:
Synthesizes proteins to be conF
ned by or associated with membranes.
Smooth endoplasmic reticulum
(
SER
)
:
Contributes to lipid metabolism, drug detoxiF
cation, and calcium regulation.
Golgi complex
:
ModiF es, packages, and trafF
cs proteins.
Lysosome
:
Degrades extraneous material.
Vesicles
:
Segregate molecules from cytosol.
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