Prokaryotes are evolutionary precursors to eukaryotes that lack a nucleus. They include organisms like Escherichia coli (E. coli). Prokaryotic cells have various parts like cell walls, plasma membranes, pili, cytoplasm, and ribosomes. However, these parts are not membrane-bound like organelles in eukaryotes. The prokaryotic DNA exists in a condensed nucleoid region. Prokaryotes reproduce through binary fission, where the cell duplicates its DNA and divides in two.

1. Prokaryotes
Stephen Taylor
i-Biology.net
Image: Hospital-associated MRSA by NIAID on Flickr http://flic.kr/p/a4RLq5

2. Prokaryotes
“Before nucleus:” evolutionary precursors to eukaryotes.
Escherichia coli (E. coli) http://en.wikipedia.org/wiki/Escherichia_coli

3. Prokaryotic Cell Parts
mesosome
cell wall
plasma membrane
pili
cytoplasm
nucleoid
ribosomes
flagella
Prokaryotic cell parts are not generally
membrane-bound, so we don’t refer to
them as organelles.
Cell structures animation:
http://www.wiley.com/legacy/college/boyer/0470003790/animations/cell_structure/cell_structure.swf

4. Prokaryotic Cell Parts
mesosome
cell wall: protective protein-based coating (Gram + / Gram -)
plasma membrane: selectively permeable, controls entry & exit of
materials to and from the cell.
pili: attach to other bacteria for DNA transfer
cytoplasm: contains enzymes for metabolic reactions
nucleoid: closed-loop of bacterial DNA in a condensed area
ribosomes: protein synthesis (transcription & translation)
flagella: whiplash-like motion causes movement
Cell structures animation:
http://www.wiley.com/legacy/college/boyer/0470003790/animations/cell_structure/cell_structure.swf

5. Prokaryotic Cell Parts
mesosomes
These don’t really exist naturally as bacterial cell parts, and could
be an example of a paradigm shift in thinking.
They were observed in some electron micrographs and thought to
be in-folds of membrane used for division, respiration or making
cell walls…
… turns out they are an
artifact of the
preparation method
for some electron
microscope images.
http://en.wikipedia.org/wiki/Mesosome
Cell structures animation:
http://www.wiley.com/legacy/college/boyer/0470003790/animations/cell_structure/cell_structure.swf

6. Past-paper question: E. coli TEM image
Identify these structures:
I.
II.
III.
IV.
Calculate the magnification of the image.
Image from IB Biology QuestionBank CDRom – get a copy here: https://store.ibo.org/biology

7. Past-paper question: E. coli TEM image
Identify these structures:
I. Plasma membrane
II. Cell wall / pili
III. Nucleoid
IV. Cytoplasm / ribosomes
Calculate the magnification of the image.
1. Measure the scale bar in mm.
2. Multiply x 1000 to convert to μm.
That is the magnification.
How long is the bacterium?
Image from IB Biology QuestionBank CDRom – get a copy here: https://store.ibo.org/biology

8. PROKARYOTES
E
P
R
O
D
U
C
E
through
binary fission
two-parts splitting

9. PROKARYOTES
binary fission
E through
P
R
The closed-loop DNA of the
O
bacterium makes copies through
semi-conservative DNA replication.
D
U New plasmids are pulled to opposing
poles by the spindle fibres.
C
The bacterium divides in two.
E

10. http://www.youtube.com/watch?v=gEwzDydciWc

11. How dirty is your phone? http://www.youtube.com/watch?v=4lmwbBzClAc

12. Prokaryotes divide by binary fission.
Life cycle of E. coli from: http://en.wikipedia.org/wiki/Escherichia_coli

17. A man got sick from E. coli after eating old sausages.
He’d contracted a porkaryote.
Photo: Sausages by Paul Hickman on Flickr (CC) http://flic.kr/p/bzcFSn

18. For more resources & links.
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