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Instruction 1-5

Cell Membrane | Enzymes | Prokaryotic and Eukaryotic Cells | RNA's Role | The Role of the Endoplasmic Reticulum and the Golgi Apparatus | Energy Capture and Storage | Mitochondria | Macromolecules | What Determines the Eukaryotic Cell's Shape? | Summary

The Role of the Endoplasmic Reticulum and the Golgi Apparatus
CA GR.9-12 Biology 1.e.

Cell Structure

Plant cellLet’s do a little review of basic cell structure. The three main parts of a cell are:

Every cell is contained within a membrane. But plant cells also have an extra cell wall around the outside of the membrane while animal cells do not.

Inside the cell membrane there is the cytoplasm (also called “cell fluid” or cytosol). This cytoplasm is actually not just “fluid" -- it is a complex system of fibers, tubes, membranes, particles and organelles (little organs), all of which have very specific functions.

At the center of it all is the nucleus, which contains DNA, the genetic material we learned about in our last Instruction.


These are relatively tiny organelles. There are two different kinds of ribosomes: free ribosomes (which float “free” in the cytoplasm) and bound ribosomes (which are attached, to something called the endoplasmic reticulum).

Ribosomes are so important because they assemble (“sequence”) amino acids into proteins (as we also learned in our last Instruction). If a protein is going to be used inside the cytoplasm of a cell, it is generally built by free ribosomes and not by ones bound to the endoplasmic reticulum.


The Endoplasmic Reticulum

This brings us to an organelle called the Endoplasmic Reticulum. Scientists call it “ER” (like the TV show).

There are two different kinds of ER:

  • Smooth ER
  • Rough ER

Smooth ER is not involved in protein synthesis. It is the site of the synthesis of fatty acids and phospholipids. It is called “smooth” because it has no ribosomes on its surface. It is shaped like little tubes, as you can see in this illustration:

Smooth ER creates steroids and stores ions so that the cell can have them when it needs them. Don’t get hung up on words like ions, we will talk about those in a later lesson. The word ion just means that a molecule has a charge. The storage of steroids and ions is kind of like keeping extra money in a savings account for when you need it later.

Smooth ER’s enzymes catalyze lots of different reactions. It detoxifies poisonous substances in the liver, for example. Smooth ER actually has an association with drug tolerance. Alcoholics have a lot more Smooth ER than people who don’t drink.

As people consume more alcohol, they realize that they have to continue to drink more to get the same effect. This happens because more inactivating enzymes are being produced.

These inactivating enzymes are responsible for helping to detoxify the liver. A body’s production of more Smooth ER is just an example of how it tries to protect you from the toxic effects of alcohol. 

Rough ER

Rough ER gets its name because its surface is studded (covered) with ribosomes, which make it look bumpy or “rough” under a microscope.

These ribosomes are said to be “bound” to the ER. The largest number of bound ribosomes is found in cells that produce secretory products.

These secretory proteins (enzymes) are manufactured here. The term secretory just means that these proteins are made for secretion, or delivery outside the cell, into the body.

Once a protein has been synthesized (made), Rough ER creates a bubble around it by pinching off a portion of its own membrane. This bubble is called a “transition vesicle.”
The transition vesicle then moves either to the cell membrane or to the Golgi Apparatus.

The Golgi Apparatus

What’s the Golgi Apparatus?

First, you need to learn to pronounce it.  The first three letters, G-O-L are pronounced “goal” and the last two
letters, G-I, are pronounced “gee.” So Golgi is pronounced goal-gee.

The Golgi Apparatus was named for Camillo Golgi, the Italian physician who discovered it. It is sometimes also called the Golgi Body, the Golgi Region or the Golgi Complex (probably just to confuse us).

The Golgi Apparatus looks like a loose stack of pancakes. Plant cells contain many of these stacks, while animal cells have just a few.

The Golgi takes simple molecules it gets from the Rough ER and makes them bigger. Remember the transition vesicles? Well, these little transported packages, or vesicles have their contents modified inside the Golgi apparatus. Not only do these little packages get modified, they get “addressed” for delivery to their next destination. The packages that now carry the modified contents are called secretory vesicles.  You might want to look back it will make this a lot easier to understand.

Here's how it works:

  • Rough ER sends simple protein molecules to the Golgi Apparatus. As you already learned, these molecules are called transition vesicles.
  • The Golgi Apparatus absorbs these transition vesicles though one side of its membrane.
  • It then converts the simple molecules into larger ones. These  larger molecules get packaged into  secretion vesicles.
  • The Golgi Apparatus then releases these secretion vesicles out of the other side of its membrane into the cytoplasm.
  • From there, the secretion vesicles move on to the cell membrane and are released out of the cell. This helps the transition work more smoothly.

In many cases, the Rough ER, the Smooth ER and the Golgi Apparatus are actually attached to one other. This helps them work easily together -- even if what they do does sound pretty complicated to us.

Video Instruction
*Availability of You Tube video links may vary. eTAP has no control of these materials.

Experiments for Home and Classroom

On this web site, called The Virtual Cell, students are invited to take a self-guided tour of various organelles within a cell. Click on the appropriate organelle for the tour and information. Then (virtually) cut the organelle in half to see what's inside. Click on the strange pink folded thing in the upper part of the Cell diagram -- it represents the Rough ER, the Smooth ER and the Golgi Apparatus. Go to:

In this activity, students are invited to build a model of a cell and then see how it divides. Each student starts out with a bowl of Jell-O™ -- and various edible objects are added to represent various organelles. The endoplastic reticulum (ER) and the Golgi Apparatus are represented by Fruit Roll-Ups™. At the end of activity, the "cell" can be eaten. Scroll down to "Make a Cell." Click: 


Reading List
from the California Department of Education
  Jones, Charlotte Foltz: Fingerprints and Talking Bones: How Real-Life Crimes Are Solved


for Students, Parents and Teachers

Now let's do Practice Exercise 1-5(top).


Next Page:  Energy Capture and Storage (top)