Page 14 - Demo 1

STRUCTURE AND FUNCTION OF MAJOR SUBCELLULAR ORGANELLES

Organisms are composed of cells and these cells have specific
structures within them that allow them to carry out their funcons. As shown in
Figure 1B, a eukaryoc cell is highly compartmentalized. These compartments,
called organelles, perform specialized funcons that together allow the cell to
be more efficient and successful.

A eukaryoc cell can be viewed as a system of interconnected organelles
that work together to facilitate and control life processes. Under the
microscope, one of the most visible organelles is the nucleus. The nucleus is a
compartment that contains the genec material that carries hereditary
informaon. Inside the nucleus, the DNA is wound ghtly around proteins and
packaged into compact units called chromosomes.
The nucleus communicates with ribosomes in the cytoplasm, and the
organelles of the endomembrane system. The endomembrane system
consists of the nuclear envelope, the membranes of the endoplasmic reculum,
the Golgi apparatus, and several vesicles. The endoplasmic reculum (ER) is an
extensive system of membranous channels and interconnecons that is
connuous with the outer membrane of the nuclear envelope. The surface of
the ER, studded with ribosomes and called the rough ER, is the site where the
cell synthesizes proteins intended for export (such as enzymes secreted from
the cell surface). Regions of the ER that do not have aached ribosomes, called
the smooth ER, aid in the manufacture of lipids such as phospholipids and
steroids.

As new molecules are synthesized on the surface of the ER, they are
passed from the ER to flaened stacks of membrane called the Golgi apparatus.
The funcon of this organelle includes collecon, packaging, and distribuon of
molecules manufactured in the cell.
The rough ER, smooth ER, and Golgi apparatus work together as a
transport system in the cell (Figure 2). Proteins and lipids produced on the ER
membranes are transported throughout the channels of the ER and are
packaged into transport vesicles – small membrane-bound sacs that bud off
from the ER.

The endomembrane system works as shown in the illustraon that
follows: (1) the vesicles fuse with the membrane of the Golgi, dumping its
content into the organelle; (2) within the Golgi apparatus, the molecules
contained in the vesicles collect at the end of the membranous folds may take
one of many paths; (3) and (4) vesicles that disintegrate from the ends carry

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