Prokayotic vs Eukaryotic Cells Functional Anatomy

Typical Bacterial Cell

Typical Eukaryotic Cells

Prokaryote vs Eukaryote Overview  Prokaryote or “before nucleus” –no membrane-bound nucleus –no other membrane-bound organelles –DNA not associated with histones –cell walls almost always contain peptidoglycan –70s ribosomes –Largest about size of smallest eukaryote  Eukaryote or “true nucleus” –membrane bound nucleus –many other membrane- bound organelles –DNA associated with histones –cell walls never contain peptidoglycan –80s ribosomes –Smallest about size of largest prokaryote

Prokaryotic Cells  Size –Smallest of living cells »0.2 to 2.0 μm in diameter »2 to 8 μm in length –Most eukaryotes bigger –Viruses much smaller

Common Bacterial Shapes  Cocci - spherical  Bacilli – rods  Spirillum - spiral

Other, Less Common Shapes  Vibrio – comma  Coccobacillus -  Square  Star

Common Cell arrangements  Cocci  Bacilli

Prokaryotic Anatomy from the Outside In  Glycocalyx  Appendages  Cell Wall  Bacterial Cell Membranes  Inside the Cell

Glycocalyx  Sticky substances that surround cells –Firmly attached = capsule –Loosely attached = slime layer  Composition varies with species –Polysaccharides –Polypeptides –Both  Function –Protect cell from phagocytosis and dehydration –Aid in attachment to various surfaces –May inhibit movement of nutrients from cell

Appendages  Flagella –Tail-like structures extending out from glycocalyx –Functions in movement of the bacterial cell –Complex structure

Structure of Flagella  Filament –Long tail-like region –Constant diameter –Made of protein  Hook –Filament attachment  Basal body –Small central rod inserted into a series of rings

Cell Wall  Rigid  Composed mostly of peptidoglycan –Found only in bacterial cell walls –Amount differs in gram+ and gram - cells  Protects cell in environments with osmotic pressures

Peptidoglycan  Glycan portion –NAG »N-acetylglucosamine –NAM »N-acetylmuramic acid –Linked in rows of sugars  Peptide portion –Adjacent rows are linked by polypeptides

Gram + Cell Wall

Gram – Cell Wall

Atypical Cell Walls  Mycoplasmas –Lack cell wall –Smallest known bacteria  Archeobacteria –Cell walls contain pseudomurein rather than peptidoglycan –Lacks D-amino acids found in bacteria  L-forms –Tiny mutant bacteria with defective cell walls –Just enough material to prevent lysis in dilute environments

Inside the Cell Wall  Cell Membrane  Cytoplasm –4/5 water and 1/5 dissolved substances –Most chemical reactions occur here  Ribosomes –Abundant in cytoplasm –70s  Nuclear region –Central 10% of cell volume –DNA in single circular chromosome  Inclusions –small bodies within cytoplasm –Many different types