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Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• The largest organelle is usually the nucleus

• The nucleus is separated from the cytoplasm by the nuclear envelope

• The nucleus is the cellular control center

– It contains the DNA that directs the cell’s activities

4.6 The nucleus is the cell’s genetic control center

ORGANELLES OF THE ENDOMEMBRANE SYSTEM


Figure 4.6

Chromatin

Nucleolus

Pore

NUCLEUS

Two membranesof nuclearenvelope

ROUGHENDOPLASMICRETICULUM

Ribosomes


Ribosomes-non-membrane bound organelles

• Ribosomes are free or attached to the endomembranous system of endoplamic reticulum

• They are where proteins are built.


• The endomembrane system is a collection of membranous organelles

– These organelles manufacture and distribute cell products

– The endomembrane system divides the cell into compartments

– Endoplasmic reticulum (ER) is part of the endomembrane system

4.7 Overview: Many cell organelles are related through the endomembrane system


• The rough ER manufactures membranes• Ribosomes on its surface produce

proteins

4.8 Rough endoplasmic reticulum makes membrane and proteins

1 2

3

4Transport vesiclebuds off

Ribosome

Sugarchain

Glycoprotein

Secretory(glyco-) proteininside transportvesicle

ROUGH ER

PolypeptideFigure 4.8


• Smooth ER synthesizes lipids

• In some cells, it regulates carbohydrate metabolism and breaks down toxins and drugs

4.9 Smooth endoplasmic reticulum has a variety of functions


SMOOTH ER

ROUGHER

Nuclearenvelope

Ribosomes

SMOOTH ER ROUGH ER

Figure 4.9


• The Golgi apparatus consists of stacks of membranous sacs

– These receive and modify ER products, then send them on to other organelles or to the cell membrane

4.10 The Golgi apparatus finishes, sorts, and ships cell products


• The Golgi apparatus

Golgiapparatus

“Receiving” side ofGolgi apparatus

Transportvesiclefrom ER

Newvesicleforming

Transport vesiclefrom the Golgi

Golgi apparatus

“Shipping”side of Golgiapparatus Figure 4.10


• Lysosomes are sacs of digestive enzymes budded off the Golgi

4.11 Lysosomes digest the cell’s food and wastes

LYSOSOME

Nucleus

Figure 4.11A


• Lysosomal enzymes

– digest food

– destroy bacteria

– recycle damaged organelles

– function in embryonic development in animals


Figure 4.11B

Rough ER

Transport vesicle(containing inactivehydrolytic enzymes)

Golgiapparatus

Plasmamembrane

LYSOSOMES

“Food”

Engulfmentof particle

Foodvacuole

Digestion

Lysosomeengulfingdamagedorganelle


• Lysosomal storage diseases are hereditary

– They interfere with other cellular functions

– Examples: Pompe’s disease, Tay-Sachs disease

4.12 Connection: Abnormal lysosomes can cause fatal diseases


• Plant cells contain a large central vacuole

– The vacuole has lysosomal and storage functions

4.13 Vacuoles function in the general maintenance of the cell

Centralvacuole

Nucleus

Figure 4.13A


• Protists may have contractile vacuoles

Figure 4.13B

Nucleus

Contractilevacuoles

– These pump out excess water


• The various organelles of the endomembrane system are interconnected structurally and functionally

4.14 A review of the endomembrane system

Transport vesiclefrom ER

Rough ER

Transport vesiclefrom Golgi

Plasmamembrane

Vacuole

LysosomeGolgiapparatusNuclear

envelopeSmooth ER

Nucleus

Figure 4.14