Chapter 4
A Tour of the Cell
Overview
The cell is the fundamental unit of life and for many of the organisms on the planet it represents the highest
level of complexity. Cells may be grouped into two general categories: prokaryotes, or those lacking a nucleus
and internal membrane system, and eukaryotes, or those who possess a nucleus and membrane system. This
unit will examine the principles of the cell theory, the structure of the cell and the role of the major organelles of
the cell. In addition, we will examine the role of the plasma membrane (to be explored more fully in Chapter 5),
the internal "skeleton" of the cell and the methods by which cells join to form larger, more complex organisms.
We will also present a comparison of plant and animal cells which will be useful in later lectures.
Assigned Reading
Text, Pages 51-69
PowerPoint Presentation
Chapter Review, Page 70
Testing Your Knowledge, Page 71
Key Terms
 Cell
 Cell theory
 Plasma membrane
 DNA, chromatin
 Eukaryote, prokaryote
 Nucleus, nucleolus, nuclear membrane, nuclear pore
 Ribosome
 Endomembrane system (also called cytomembrane)
 Endoplasmic reticulum (smooth & rough)
 Golgi apparatus
 Vacuole, lysosome, peroxisome
 Mitochondria
 Chloroplast, amyloplast
 Microtubule, microfilament, intermediate filament
 Centriole
 Extracellular matrix
 Tight junction, anchoring junction, gap junction
 Plasmodesmata
Introduction
The study of cellular function is an extremely important aspect of biology. Since all organisms are comprised of
cells, and we have defined the cell as the basic unit of life, we must understand the structure and function of the
cell before proceeding into discussions of metabolism and genetics later.
To better visualize the cell, I suggest that you think of it as a biological factory. The purpose of this factory will
be to produce the materials needed for life, but our cellular factories are very similar to modern day structures.
For the sections below, you should focus on the major roles of the organelles in the cell.
Throughout this lesson, use your text to visualize the appearance and location of these structures.
Prokaryotic vs. Eukaryotic Cells
The PowerPoint presentation introduces two types of cells: prokaryotic and eukaryotic. While this course will
focus on the structure and function of a eukaryotic cell, we will spend a moment on the prokaryotes.
Prokaryotic cells are the simplest of all cells. They are typically small (less than 10 um) and do not possess a
nucleus or any membrane bound organelles. Bacteria are prokaryotic cells, and although simple they represent
one of the greatest threats to our species.
Eukaryotic cells are typically about 10x larger than prokaryotic cells (some border on the visible range) and have
a nucleus and other membrane bound organelles. This internal compartmentalization of the eukaryotic cell
results in the ability to specialize cellular functions as we will see in this chapter. The next chapter will discuss
the cell membrane in more detail, but these concepts are important.
For a comparison of the size difference between a prokaryotic and eukaryotic cell, click here
Nucleus
The nucleus is the command center of the cell. Surrounded by the nuclear envelope, it isolates the DNA from the
remainder of the cell. The nuclear envelope is made from a bilayer of the biomolecule called phospholipids. As
we will see, all of the internal membranes of a eukaryotic cell are made from phospholipids. Note the function
of the nucleolus is the manufacture of ribosomes. Ribosomes are involved in the synthesis of proteins, the
working molecules of the cell.
The nucleus houses the genetic material, DNA, and in this chapter we introduce the term chromosome. We will
explore chromosomes again later, but for now consider them to be the storage system for the DNA of the cell.
Endomembrane System
The Endomembrane system is an extensive network of membrane-bound organelles, all made from
phospholipids. This similarity in their construction material will become very important in a few moments.
Endoplasmic reticulum: Note the two different types of ER, smooth (SER) and rough (RER). Also note that each
has a different function for the cell. The ER is connected to the nucleus at the nuclear pores.
Golgi bodies (also known as the Golgi complex or Golgi apparatus): The processing center for the cell. Most
biomolecules pass through the Golgi before their final destination (either internal use or export). The
biomolecules made in the RER and SER are processed in the Golgi using the pathway described in your text.
Note how important it is that the ER, the vesicles that contain the biomolecules, and the Golgi, all be composed
of the same compounds. This allows for an interchangeability of the cytomembrane system. This gives the cell
the ability to adapt to changes rapidly.
Peroxisomes and lysosomes: Our biological factory has a need for processing incoming raw materials and
detoxifying waste materials. These organelles perform these tasks.
Special Organelles
The mitochondria and chloroplast presented in this section are independent of the cytomembrane system
presented above, although they are made from phospholipids as well. We will spend entire chapters on the role
of the mitochondria (cellular respiration) and chloroplast (photosynthesis). For now, understand their general
roles in the function of our biological factory.
Cytoskeleton
Just like in a factory, a cell requires an internal framework to organize the cellular functions, provide mobility if
needed and shape to the cell. The cytoskeleton provides that. There are three major parts to the cytoskeleton:
the microtubules, microfilaments and intermediate filaments. We will discuss each of these in considerable
detail in later chapters. Here you should get a general idea as to their function, but do not focus on their
structure at this time.
Cell Structure Factory Analogy—We talked about how the parts of a cell are like the areas of a factory. Let’s
expand that a bit and explore how a factory (cell) manufactures and ships a product. A factory’s main control
center is the office building where the managers work (nucleus). Information comes into this building from the
rest of the factory and from outside, letting the managers know what needs to be done within the factory. Our
factory/cell needs to make a certain widget, so the office/nucleus looks at blueprints (DNA) for the widget, makes
a copy (RNA), and sends it through the mail chutes (nuclear pores). These blueprints then go to the factory floor
(endoplasmic reticulum) where automated machinery (ribosomes) assemble the parts (amino acids) into the
completed widget (protein). The widget then goes to the shipping room (Golgi apparatus) for packaging and
mailing. The packaged widgets get sent to other parts of the factory, or out of the factory building to other
locations. The factory itself is built on a specific framework (cytoskeleton) that holds the various departments
and internal shipping roads or corridors. The factory needs electricity to fuel its machinery, and has several
power plants (mitochondria) on-site to provide this energy.
Movement
Not all cells move, but those which do use one of three methods: pseudopods, flagella or cilia. These may all be
considered extensions of the cytoskeleton from above.
To see the cells moving, click here (requires a downloading of a .mov file)
For a more detailed explanation of cilia and flagella (and the cytoskeleton system), click here.
Concepts
 Know the principles of the cell theory.
 Know the differences between prokaryotic and eukaryotic cells
 Know the differences between plant and animal cells.
 Know the function, cellular location, and importance of the organelles of a cell.
 Understand the endomembrane system, what components are included, and how things move between
them.
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Understand the role of the cytoskeleton to the cell and the key terms associated with it.
Understand the process of cellular mobility.
Recognize the types of junctions between cells, as well as their function.
Links of Interest
Cells Alive—a well presented site exploring the inner workings of cells.
Review Material
MyBiology.com—Study guides and resource for this text. Specifically look at MP3 Tutor and all Web Activities