Study hint: Read chapter 2 in your textbook. Follow the outlines in your syllabus carefully as you memorize the structure and function of each major organelle and the description of the major cellular processes.

In this lecture, definitions or important images are located in pop-up windows. Students who already studied the cell extensively in other courses may choose to ignore the opportunities to view this material. Read these lectures with your Syllabus beside you. Record descriptions included in the pop-up windows in the outlines in your syllabus.
I am indebted to the LifeArt Collection, copyright 1994, TechPool Studios Corporation, for the images used in this lecture.

Key Structures of the Eucaryotic Cell

• The Plasmalemma
• Membranous Organelles
• Tubular organelles
• Ribosomes
• Inclusions

Important Cellular Functions

• Organelle-dependent Functions
• Diffusion and other Passive Processes
• Active Transport
• Endocytosis
• Exocytosis
• Mitosis
• Meiosis in Gametes

Key Structures of the Eucaryotic Cell

We must begin our discussion of the key structures of the animal cell with a look at the "limiting membrane" of the cell--the Plasmalemma aka plasma membrane aka cell membrane. This membrane separates two "rooms" called compartments--the intracellular fluid (ICF) compartment from the extracellular fluid (ECF) compartment. Substances moving into or out of the cell must cross it using either an active or passive process.

Let's stop a moment and consider the extracellular environment of the cell. Without getting into topics we will discuss at length in "Human Physiology", think about the numerous molecules traveling in the ECF. One very important class of substances traveling in the ECF is called a ligand. In fact, the cell surface is very complicated. Attached to the external face of the plasma membrane are sugars called glycolipids and glycoproteins. When I was in school many years ago ;-) , these molecules were called the "cell coat". These substances help cells identify one another-- that is, they are important in the process of cell recognition. Integral proteins are embedded in only the external face, only the internal face, or pass through both sides of the membrane. These transmembrane proteins act as channels that move some materials into the cell under certain conditions. Peripheral proteins are not attached to the plasmalemma.

The drawing of the generalized animal cell on page 29 of your textbook is a good place to begin a careful study of both membranous and tubular organelles. One word of caution: this diagram shows all organelles found in all the cells in the body. No cell in the body contains both microvilli and microtubules!! Notice that the membranous organelles contain "membrane" similar in structure to the plasmalemma. Membranes surround spaces or compartments that may have specific names. Look at a mitochondrion (plural--mitochondria). Identify the two spaces inside this unusual organelle.

Tubular organelles are part of the cytoskeleton. They always contain a characteristic protein and are small (about 5 nm), intermediate (around 10 nm), or large (greater than 15 nm) in size. Whereas microfilaments contain actin, microtubules contain the protein tubulin. The protein found in intermediate filaments varies depending upon the cell type under study. "Coronin" is also a protein that is important in the cytoskeleton, and is a topic of ongoing research.

Important Cellular Functions

Memorize the organelle-dependent functions listed for each organelle in chapter 2. The information written inside the functions boxes included with the figures in this chapter is vital to your understanding of the cell. Do not skip this information.

I already noted that the plasmalemma separates the extracellular fluid space from the intracellular fluid space which contains the cytosol. Substances in the extracellular fluid enter the cell under certain conditions; and substances inside the cell may be "secreted" into the extracellular space. Your textbook considers passive and active processes in detail in the beginning of chapter 2. One question that has always bothered me is what happens to the cytoskeleton during a process like phagocytosis. Think about it. Phagocytosis must severely deform the cytoskeleton. This process makes me appreciate how flexible the cytoskeleton really is. It is definitely not as rigid as a human skeleton!

I would like to add another very important concept to your thinking. We usually consider active and passive processes when we are talking about the plasmalemma. However, once a substance enters the cell--through diffusion, facilitated diffusion, active transport or endocytosis--that substance may be used by a membranous, cellular organelle in a series of chemical reactions that I have referred to as organelle-dependent functions. If a substance must enter an organelle to participate in a chemical reaction, the substance must cross at least one, and many times, two membranes to move inside the organelle. As you think about these processes, remember that some of these same processes must occur to move substances into mitochondria or even into the nucleus of the cell. Passive and active processes are the only way across a membrane. More about this in Physiology!

Mitosis

Meiosis