Download Introduction to Prokaryotes versus Eukaryotes

Name___________________________________________________Date_____________
Introduction to Prokaryotes & Eukaryotes
The modern electron microscope has been especially valuable in viewing the organelles of the
prokaryote cell, such as a bacterial cell. Such cells are only about 1/10 the size of a typical
eukaryote cell, and they are much simpler in their structural design. As you examine Figure 5.2,
note that the prokaryote bacterial cell lacks a true nucleus. Prokaryotic cells appeared “before”
(pro-) nuclei had evolved. Instead of a nucleus, the bacterium has a central, oval shaped,
nucleoid region that is “kernel-like,” but which is not surrounded by its own individual
membrane. The nucleoid region contains a complex collection of coiled DNA molecules. These
DNA molecules use RNA molecules to direct and control the activities of the other organelles.
The most prominent organelles are the ribosomes or “5-carbon sugar” (rib) “bodies” (- somes).
The ribosomes are tiny black bodies containing the 5-carbon sugar, ribose. These black bodies
are the main locations for
protein synthesis in the
bacterial cell.
Like most other cells, the
bacterial cell is surrounded
by a soft cell membrane (also
called plasma membrane).
This membrane encloses the
cytoplasm and most other
organelles. In addition,
bacteria have a rigid cell
wall: a protective barrier
outside the soft cell
membrane. The third and
outermost layer is the
bacterial capsule, which is a
sticky coat that helps glue
some types of bacteria to
surfaces of other cells.
Fig. 5.2 Anatomy of a typical prokaryotic bacterial
cell.
Two types of projections
often extend from the
bacterial surface: pili, short,
“hair”-like strands, and
flagella, long, “whip”-like
strands. The pili help the
bacterium attach itself to
other objects, while each flagellum acts
like a whip to push the cell through its
watery surroundings.
Name___________________________________________________Date_____________
Eukaryote Cells: Plant and Animal Cells
Plant and animal cells have a much more complex structure than a bacterium. As eukaryotes,
both types of cells have their own well-defined nucleus, surrounded by a nuclear membrane.
Of the two eukaryote
types, the plant cell has
more in common with the
bacterial cell. Note from
Figure 5.3, A that the
plant cell, like the
bacterium, is surrounded
by a rigid cell wall.
Likewise, plant cells have
a plasma (cell) membrane
immediately inside the
cell wall. This is different
from the typical animal
cell (Figure 5.3, B), which
has only a plasma
membrane surrounding it.
Fig. 5.3 Typical eukaryotes – plant and animal cells. (A) Plant cell
anatomy. (B) Animal cell anatomy.
The plant cell has its green
chloroplasts filled with
chlorophyll, and a large
central vacuole. The
central vacuole lies near
the center of the cell, and
it appears to be “empty”
or clear when viewed
through a light
microscope. In reality, it is
a storage sac for various
digestive enzymes. This
makes the central vacuole
in the plant cell the rough
equivalent of the animal
cell’s lysosome or
“breakdown” (lys) “body”
(som), which also contains
digestive enzymes that
digest or break down
foodstuffs and other
materials within the cell.
Name___________________________________________________Date_____________
Both types of eukaryotic cells have numerous mitochondria. The mitochondria are nicknamed
the “powerhouse” of the cell because they are the site of aerobic respiration and ATP (energy)
production. Also present in both cell types is an endoplasmic reticulum. The endoplasmic
reticulum, or ER, is literally a “tiny network present within the cytoplasm.” The ER is a complex
network of flattened sacs that carry things around in the cell, much like a miniature circulation or
highway system. The rough ER gets its name from the fact that its “rough” surface is studded
with many ribosomes. The smooth ER does not have any ribosomes attached to its surface. The
ribosomes on the rough ER engage in protein synthesis.
The synthesized proteins are then circulated to the Golgi body or apparatus. The Golgi
body/apparatus is named after its discoverer, Camillo Golgi, a histologist, or “one who
specializes in the study of tissues.” The Golgi body consists of a series of tightly stacked,
flattened sacs. It mainly serves to package the proteins, lipids, hormones, and various other
products of the cell.
Finally, both plant and animal cells contain a cytoskeleton. The cytoskeleton is literally the
“skeleton” of the cell, giving it some rigidity and support. The cytoskeleton consists of both
hollow microtubules and solid microfilaments.
1. Describe the size difference between prokaryotic and eukaryotic cells.
2. Why are ribosomes important?
3. Describe three similarities between prokaryotic and eukaryotic cells.
4. Describe three differences between prokaryotic and eukaryotic cells.
5. Describe three similarities between plant and animal cells.
6. Describe three differences between plant and animal cells.
Name___________________________________________________Date_____________
Describe the job of each organelle, and color the structures as indicated:
Mitochondria (red):
Chloroplasts (green):
Cell Wall (brown):
Lysosome (orange):
Golgi Body (blue):
Nucleus (purple):
DNA:
RER & SER (yellow):
Cytoskeleton (black):
Cell Membrane (pink):
Flagella (red):