Microbiology Lecture 4

Bacteria

Cell size

Size range for prokaryotes: 0.2 µm to >700 µm in diameter

Most cultured rod-shaped bacteria are between 0.5 and 4.0 µm wide and <15 µm long

Cell morphology

Morphology = cell shape 

Major cell morphologies: 

• Coccus (pl. cocci): spherical or ovoid
• Bacillus (pl. bacilli): rod or cylindrical shape
• Spirillum (pl. spirilla): spiral shape

Cells with unusual shapes: Spirochetes, appendaged bacteria, and filamentous bacteria 

Many variations on basic morphological types

Cytoplasmic membrane:

• Thin structure that surrounds the cell
• 6–8 nm 
• Vital barrier that separates cytoplasm from environment
• Highly selective permeable barrier; enables concentration of specific metabolites and excretion of waste products

Function

Permeability Barrier 

• Polar and charged molecules must be transported
• Transport proteins accumulate solutes against the concentration gradient

Protein Anchor

• Holds transport proteins in place

Energy Conservation

The bacterial cell wall

Peptidoglycan 

Rigid layer…