Biology (Holt)

Packaging and Distribution of Proteins

Vesicles that contain newly made proteins move through the cytoplasm

from the ER to an organelle called the Golgi apparatus. The

(GOHL jee) is a set of flattened, membrane-bound sacs that

serves as the packaging and distribution center of the cell. Enzymes

inside the Golgi apparatus modify the proteins that are received in

vesicles from the ER. The modified proteins are then enclosed in new

vesicles that bud from the surface of the Golgi apparatus. Some of

these vesicles include (LIE seh sohms), which are small,

spherical organelles that contain the cell’s digestive enzymes. The ER,

the Golgi apparatus, and lysosomes work together in the production,

packaging, and distribution of proteins, as summarized in Figure 15.

Step Ribosomes make proteins on the rough ER. The proteins

are packaged into vesicles.

Step The vesicles transport the newly made proteins from the

rough ER to the Golgi apparatus.

Step In the Golgi apparatus, proteins are processed and then

packaged into new vesicles.

Step Many of these vesicles move to the cell membrane and

release their contents outside the cell.

Step Other vesicles, including lysosomes, remain within the

cytoplasm. Lysosomes digest and recycle the cell’s used

components by breaking down proteins, nucleic acids,

lipids, and carbohydrates.

lysosomes

apparatus

Golgi

64 CHAPTER 3Cell Structure

BIO

graphic

CHAPTER 10 How Proteins Are Made

ribosomes on the

rough ER.

Processing of Proteins

1

Vesicles carry proteins

from the rough ER to

the Golgi apparatus.

Proteins are modified in the Golgi apparatus and 2

enter new vesicles.

3

Some vesicles release

their proteins outside

the cell.

4

Other vesicles remain in

the cell and become

lysosomes.

5

Nucleus

Proteins are processed by an internal system of membranes.

Figure 15

Interpreting Graphics

As you read, use Steps 1–5

in the text, shown in red, to

help you follow the same

numbered steps shown in

Figure 15.