Eukaryotes and Prokaryotes

Prokaryotes includes the bacteria Karyote means nucleus

Prokaryotes do not have a membrane bound nucleusThe nuclear material is free in the cytoplasm

It does not wrap around histone proteins to form chromosomes

DNA

Cytoplasm

Prokaryotes have no membrane bound organells

Some functions like respiration take place on folds of the cell surface membrane called mesosomesThe enzymes required are embedded in the membrane

Cell membrane

mesosomes

Prokaryotes have 70S ribosomes free in the cytoplasm

70S Ribosomes

Prokaryotes have a cell wall made of peptidoglycan

This may be surrounded by a slime capsule

Peptidoglycan cell wall

Slime capsule

Prokaryotes may have a flagellum for movement

The structure of proteins inside the flagellum is different to that in Eukaryotes

Some Prokaryotes have many cytoplasmic projections called Pili

Flagellum

Eukaryote means “true nucleus”

Eukaryote cells have a nucleus with a nuclear envelope They have membrane bound organelles

Chloroplasts and mitochondria have a double membrane

The Endosymbiont Theory

• Chloroplasts and Mitochondria are the same size as Prokaryotes (0.5 - 10µm)

• They contain 70S ribosomes and circular DNA like prokaryotes

• They have a double membrane

The endosymbiont theory suggests these organelles were once free living prokaryote organisms that were engulfed by another

cell and enclosed in a vacuole

A larger prokaryotic cell engulfs a smaller one

The smaller cell can photosynthesise because it contains chlorophyll pigments

Note the smaller cell has its original membrane and a

vacuolar membrane around it

Or a double membrane

Instead of digesting the contents of the vacuole a symbiotic relationship was established

Symbiotic relationships are those in which both parties benefit from the relationship

The larger cell receives glucose

The smaller cell is sheltered and receives other nutrients and raw materials