prokaryotes vs eukaryotes
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Prokaryotes vs. Eukaryotes. I. Structure, function, and reproduction of prokaryotes A .  Most prokaryotes are unicellular.           1.Some species form aggregates of two or more individuals . B .  Three (3) common shapes:  cocci (round); bacilli ( rod); helical (spiral).

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I. Structure, function, and reproduction of prokaryotes

A.  Most prokaryotes are unicellular.          

1.Some species form aggregates of two or more individuals.

B.  Three (3) common shapes:  cocci (round); bacilli (rod); helical (spiral)

The world of prokaryotes
  • C.  They’re everywhere!
  • Collective prokaryote biomass outweighs all eukaryotes combined by at least tenfold. 
  • They exist almost everywhere, including places where eukaryotes cannot.
  • Most prokaryotes are beneficial; we couldn’t live without them.  (e.g. Nitrogen-fixing bacteria)
Lyme disease:

Caused by a spirochete

Some cause illness à bubonic plague, diphtheria, salmonella
  • Approximately 5000 species have been identified.  Estimates of prokaryote diversity range from 400,000 to 4,000,000 species.            
  • D.  Bacteria and Achaea are the two main branches of prokaryote evolution
  • Achaea are thought to be more closely related to eukaryotes than to bacteria.
E. Most prokaryotes secrete sticky substances that form a protective layer and enable them to adhere to substrates.

1.  The sticky protective layer secreted by prokaryotes is called the capsule.

2. Some prokaryotes adhere to substrates using Pili.(Pili are thin, protein tubes originating from the cytoplasmic membrane)

a.  Some Pili are specialized for DNA transfer. This process is called conjugation; note for later in class.

F.  Almost all prokaryotes have cell walls external to the plasma membrane.

1. Cell walls maintain cell shape.

2. Cell walls are composed of peptidoglycan.(a polymer consisting of sugars and amino acids that forms a mesh-like layer outside the plasma membrane of bacteria, forming the cell wall)

G. Cellular and genomic organization of prokaryotes is different from that of eukaryotes

1.Prokaryotes have no nucleus.

2. The nucleoidregion in a prokaryotic cell consists of a concentrated mass of DNA. This mass of DNA is usually one thousand times less than what is found in a eukaryote.

components of a prokaryote
Componentsof a prokaryote
  • Cytoplasm
  • Ribosomes
  • Nuclear Zone
  • DNA
  • Plasmid
  • Cell Membrane
  • Mesosome
  • Cell Wall
  • Capsule (or slime layer)
  • Flagellum

Plasma membrane

Lipopolysaccharide layer

Outer membrane


Plasma membrane

Gram Positive

Gram Negative


Photosynthesis evolved early in prokaryotic life

Cyanobacteria started to produce O2 about 2.7 billion years ago

Contrasting hypotheses for the taxonomic distribution of photosynthesis among prokaryotes.

2.  Chlamydias

- Parasitic; survive only within cells of animals

 - Some cause STDs e.g.Chlamydia

 3.  Spirochetes

      - Helical heterotrophs

     - Some cause STDs e.g. syphilis

 5.  Cyanobacteria

         - Oxygenic photosynthesis, and chloroplasts evolved from them.

Ecological impacts of prokaryotes

A.  Prokaryotes are links in the recycling of chemical elements

B.  Many prokaryotes are symbiotic (2 organisms living in direct contact with each other).

Mutualism– both symbiotic organisms benefit

- e.g. Nitrogen-fixing bacteria like Rhizobium: plant obtain organic nitrogen, Rhizobium gets energy in the form of sugars that the plant produces.


Are all prokaryotes disease producing germs?

Without prokaryotes ecosystems would collapse!

Humans use prokaryotes in research and technology


Sewage treatment


Chemical & Medical production

Research (genetic engineering, etc.)

eukaryotic and prokaryotic cells
Eukaryotic and Prokaryotic Cells

Prokaryote = without a nucleus

Eukaryote = with a nucleus

components of a eukaryote
Components of a Eukaryote
  • Cytoplasm
  • Nucleus with Nucleolus
  • Mitochondria
  • Chloroplast
  • Ribosomes
  • Rough Endoplasmic Reticulum
  • Smooth Endoplasmic Reticulum
  • Golgi body
  • Vacuoles
components of a eukaryote continued
Components of a Eukaryote continued
  • Lysosomes
  • Cytoskeleton
  • Centriole
  • Cilium and Flagellum
  • Microvillus
  • Cell membrane
  • Cell Wall
Comparing Prokaryotic and Eukaryotic Cells



Have Organelles

Have a


Have membranes surrounding organelles

Have cell wall

or membrane

Are mostly bacteria

Include all plant and animal cells

Have DNA

Have cytoplasm