Prokaryotic and Eukaryotic Cells

Prokaryotic and
Eukaryotic Cells
Structure and Function
In general microbes or microorganisms may be either
prokaryotic (bacteria) or eukaryotic (protists, fungi,
and some animals).
However, there are some microbial organisms that
appear to be intermediates between prokaryotes and
eukaryotes (they possess a nucleus but do not have
mitochondria or chloroplasts, an example is Giardia
intestinalis.
Prokaryotes differ from eukaryotes in several ways
including but not limited to:
Characteristics Prokaryotic Eukaryotic
Types bacteria (monerans) protists, fungi, plants, and animals
Organization unicellular usually multicellular (exception some
protists)
Cell size small (0.1-10um) larger (10-100um)
Membrane-bound organelles absent present
Reproduction asexual asexual and sexual
DNA circular linear
Proteins assoc. with DNA Basic Histone
Plasma membrane No sterols Sterols
Ribosomes 70S 80S
Cytoskeleton Absent present
PROKARYOTIC
CELLS
Key Functions of Cells
A boundary that keeps the cellular contents
separate from the external environment but allows

for the transfer of some substances into and out of
the cell.
Replication of DNA
Synthesis of cellular components
The ability to obtain energy through metabolic
processes
Appendages are basically involved in
movement or adhesion
Flagella (singular flagellum)
are cellular appendages that
consist of three parts:
•
a filament that rotates for
movement
•
a hook where the filament
attaches
•
a basal body that anchors the
hook to the cell
•
the arrangement of the
hook/basal body articulation
allows the hook with its
filament to rotate 360
o
Arrangements of Flagella
polar - flagella are attached at
one or both ends of the cell
monotrichous - a single

flagellum at one end
lophotrichous -
multiple flagella arising
from one or both ends
amphitrichous – a
single flagellum arises
from each end
peritrichous - flagella are
randomly dispersed over the
cell surface
Axial filaments
are modified flagella that
occur in spirochetes
Non-locomotor appendages
Pili are longer and sparser
than fimbriae.
fimbriae are involved in
adhesion and pili (found
only in Gram - bacteria)
are involved in
conjugation ( a “mating”
process).
Cell envelopes differ between taxa
but they basically consist of three
layers:
The capsule or slime layer
(outermost layer) differs greatly in
thickness, organization and chemical
composition depending on the
bacterial species. T

Beneath the outer layer lies the cell
wall.
The cell membrane is a thin flexible
sheet that surrounds the contents of
the bacterial cell. Its functions
include: transport, energy extraction,
nutrient processing, and synthesis
The Gram Stain
An important tool in the
identification of bacteria is the
Gram stain. Some bacteria are
Gram + while others are Gram -
(some however, do not show a
Gram reaction). Gram + bacteria
stain purple (the color of the
primary dye) and Gram - bacteria
stain pink (the color of the
counterstain or second dye). The
Gram stain is a differential
staining technique because
different species of bacteria stain
differently. The difference is a
result of the composition of the
cell wall.
The protoplasm or cytoplasm
is the dense gelatinous
solution within the cell
membrane that is the
primary site for the cell’s
biochemical and synthetic

processes. The following
are found within the
protoplasm of the
prokaryotic cell:
chromatin body or the
bacterial chromosome
nucleoid or nuclear region
of the cell that is
associated with the
chromatin body
plasmids are tiny circular
extrachromosomal
strands of DNA
ribosomes are small
structures consisting of
RNA and proteins that are
involved in protein
synthesis
inclusions or granules are
areas where nutrients are
concentrated
Endospores are dormant
structures produced by
some species of Bacillus
and Clostridium.
Shapes and arrangements of bacteria
There are six common
shapes of bacteria: coccus,
bacillus, coccobacillus,
vibrio, spirochete, and

spirullum and there are
several arrangements of
these cells: single, chains
(strepto-), clusters
(staphylo-), pairs (diplo-)
etc.
Eukaryotic Cell
Cell Membrane
Cell membrane
Structure
Components
Arrangement
Functions include
Barrier
Transport (know diffusion, osmosis, facilitated
diffusion and active transport)
Recognition (e.g., self vs. non-self)
Reception (for protein hormones)
Adhesion
Nucleus
Structure and Function
–
membrane similar to cell
membrane (similar
function)
–
Nucleolus (formation of
ribosomes)
–

Chromosomes (gene
expression)
–
Nucleoplasm (matrix)
Ribosomes
•
Structure
–
rRNA
–
Proteins
•
Function
–
Site of protein formation
(translation)
•
Found in both
prokaryotes and
eukaryotes (different
structurally)
Endoplasmic Reticulum
•
Structure membranous
system of tunnels and
sacs
–
Rough – with ribosomes
on surface
–

Smooth- no ribosomes
on surface
•
Function
–
Rough – protein
synthesis
–
Smooth- lipid synthesis
Golgi Apparatus
•
Structure also
membranous, kind of
like a stack of pancakes
•
Function processing of
lipids and proteins
Lysosomes
•
Structure membrane
bound sac containing
hydrolytic enzymes
•
Function digestion