1. Chapter 3 The Cellular Level of Organization
Lecture slides prepared by Curtis DeFriez, Weber State University

2. The Cell A cell is the basic unit of all living things.
Prokaryotic cells are simple cells that are Pro (“before”) karyon (“nucleus”) – they have no nucleus.
Most are unicellular bacteria.
Eukaryotic cells are complex cells with a nucleus and subcellular structures (organelles).
All fungi, plants, and animals are eukaryotes.

3. A Generalized Cell
All eukaryotic cells are composed of three main parts:
Plasma membrane or “plasmalemma”
Cytoplasm - a gelatin-like substance, plus structural fibers and organelles (but
not the nucleus)
Nucleus - contains the
genetic library of the cell

4. A Generalized Cell
The plasma membrane forms the cell’s outer boundary and separates the cell’s internal environment from the outside environment.
It is a selectively permeable barrier,
allowing the passage of some
things and not others.
It plays a role in
cellular communication.

5. A Generalized Cell
The cytoplasm contains all the cellular contents between the plasma membrane and the nucleus.
The cytosol is the fluid portion (mostly water).
Organelles are subcellular
structures embedded
in the cytosol, having
characteristic shapes
and specific functions.

6. A Generalized Cell
The nucleus is a large organelle that contains DNA in molecules called chromosomes.
Each chromosome consists of
a single molecule of DNA and
associated packaging proteins.
A chromosome contains
thousands of hereditary
units called genes.

7. A Generalized Cell
Fig. 3.1 shows a generalized body cell labeled with the plasma membrane, cytoplasm (and organelles) and nucleus.

8. The Plasma Membrane
The plasma membrane is much more than just a “fence” – it is a flexible yet sturdy, “intelligent” semipermeable regulator that:
Covers and protects the cell
Controls what goes in and comes out
Links to other cells
Flies certain “flags” to tell
other cells “who” it is

9. The Plasma Membrane
The Fluid Mosaic Model describes the arrangement of molecules within the membrane: They resemble a sea of phospholipids with protein “icebergs” floating in it.
The lipids act as a barrier to certain polar substances.
The proteins act as
“gatekeepers”, allowing
passage of specific
molecules and ions.

10. The Plasma Membrane Interactions Animation
Membrane Functions
You must be connected to the internet to run this animation.

11. The Plasma Membrane The structure of the membrane
Phospholipids form a lipid bilayer - cholesterol and glycolipids (sugar-lipids) also contribute.
Integral proteins - extend into or through the bilayer.
Transmembrane proteins (most integral proteins) span the entire lipid bilayer.
Peripheral proteins attach to the inner or outer surface but do not extend through the membrane.

12. The Plasma Membrane

13. The Plasma Membrane
Glycoproteins are membrane proteins with a carbohydrate group attached that protrude into
the extracellular fluid.
The Glycocalyx is the entire
“sugary coating” surrounding
the membrane (made up of
the carbohydrate portions
of the glycolipids and
glycoproteins).

14. The Plasma Membrane The Functions of the membrane
Some integral proteins are ion channels.
Transporters - selectively move substances through the membrane.
Receptors - for cellular recognition; a ligand is a molecule that binds with a receptor.
Enzymes - catalyze chemical reactions
Others act as cell-identity markers.