1. Cell Structure

2. Cell Theory – again! All organisms are composed of one or more cells.
Cells are the smallest living units of all living organisms.
Cells arise only by division of a previously existing cell.

3. Cell Characteristics Genetic material
single circular molecule of DNA in prokaryotes
double helix located in nucleus in eukaryotes
Cytoplasm fills cell interior –
sugars, amino acids,
proteins - organelles
Plasma membrane encloses
the cell
Phospholipid
Membrane
proteins

4. Cell Size
Most cells are relatively small because as size increases, volume increases much more rapidly than surface area.
What difficulties result?

5. Visualizing Cells
Resolution - minimum distance two points can be apart and still be distinguished as two separate points
Compound optical microscopes - magnify in stages using multiple lenses
Transmission electron microscope - electrons transmitted through specimen
Scanning electron microscope - electrons beamed onto surface of the specimen

6. Visualizing Cells

7. Prokaryotic Cells Simplest organisms, incl. the monera (bacteria)
All have Cytoplasm, surrounded by plasma membrane and encased in a rigid cell wall (not cellulose)
No membrane-bound organelles (ie no nucleus, mitochondria, etc.)
Contain bacterial ribosomes
Contain naked DNA (nucleoid)

8. Prokaryotic Cells Some use flagellum for locomotion
threadlike structures protruding from cell surface
Bacterial cell wall
Rotary
motor
Flagellin
Sheath

9. Prokaryotic Cells
Some have pili – small thread-like structure which protrude through the cell wall.

10. Prokaryotic Cells
Many have a capsule or slime layer around the cell wall, which aids water retention.

11. Prokaryotic Cells
All reproduce a-sexually by binary fission

12. Endosymbiosis
Endosymbiotic theory suggests engulfed prokaryotes provided hosts with advantages associated with specialized metabolic activities.

13. Theory of Endosymbiosis

14. Generalized Eukaryotic Cell