Topic 2.2 Prokaryotic Cells
IB Biology 2010
Objectives
 2.2.1-Draw and Label a diagram of the
ultrastructure of Escherichia coli as an example
of a prokaryote.

2.2.2 -Annotate the diagram with the functions
of each named structure.

2.2.3-Identify structures from 2.2.1 in electron
micrographs of E. coli

2.2.4-State that prokaryotic cells by binary
fissions
What is a Prokaryotic Cell?

Cells are often divided into certain
groups based on major characteristics
◦ One such groupings divide cells into two
groups: prokaryotic and eukaryotic

Prokaryotic cells are much smaller and
simpler than eukaryotic cells
◦ Most prokaryotic cells are less than 1
micrometer in diameter
Feature of prokaryotic cells

Study Figure and be sure you can identify:
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Cell wall
Plasma membrane
Flagella
Ribosomes
Nucleoid
Electron micrographs of E. coli
Cell Wall

Prokaryotic cell wall protects and the
maintains the shape of the cell
◦ Composed of carbohydrate-protein complex
called Peptioglycan
◦ Some bacteria have an additional layer of a
type of polysaccharide outside the cell wall
 This layer makes it possible for some bacteria to
adhere to structures such as teeth, skin, and food
Plasma membrane

Located just inside the cell wall and has a
composition similar to the membrane of
eukaryotic cells
◦ Functions-controls the movement of materials
in and out of the cell. It also plays a role in
binary fission

Cytoplasm—occupies the complete
interior of the cell
Pili and Flagella

Pili-hair-like growths on the outside of the
cell wall
◦ Used for attachment, and in joining bacterial
cells in preparation for the transfer of DNA
from one cell to another

Flagella-they are longer than the pili and
allow cell motility
Ribosome

Occur in all prokaryotic cells and they
function as sites of protein synthesis
◦ They occur in very large numbers in cells
with high protein production
◦ Cause a granular appearance to an electron
micrograph
The nucleoid region


It is non-compartmentalized
Contains a single, long, continuous, circular
thread of DNA
◦ Region is involved with cell control and
reproduction

Plasmids-small, circular DNA molecules that
are not connected to the main bacterial
chromosome
◦ Replicate independently of the chromosomal
DNA
◦ Not needed for everyday functions but does help
adapt to unusual circumstances
Binary Fission

Prokaryotic cells divide by a very simple
process called binary fission
◦ During this process, the DNA is copied, the
chromosmes become attached to different
regions on the plasma membrane, and the cell
divides into two genetically identical daughter
cells.
◦ This divisional process includes an elongation
of the cell and a partitoning of the newly
produced DNA by microtubule-like fibers
made of protein called FtsZ.
Binary Fission
Summary

Here is a list of major distinguishing
characteristics of prokaryotic cells
◦ Their DNA is not enclosed within a membrane and is
one circular chromosome
◦ Their DNA is free; it is not attached to proteins
◦ They lack membrane-bound organelles. Ribosomes
are complex structures within the plasma membrane,
but they have not exterior membrane
◦ Their cell wall is made up of Peptidoglycan
◦ They usually divide by binary fission
◦ They are characteristically small in size, usually 1-10
µm