Chapter 4

Functional Anatomy of

Prokaryotic and Eukaryotic

Cells

Definition of “prokaryotic”

Refers to organisms, typically 1-celled,

having cells which: – lack a nucleus

– lack membrane-bound organelles

– contain 1 chromosome

– may contain extra-chromomal DNA (plasmids)

– contain 70S ribosomes

– contain peptidoglycan cell walls

Prokaryotic vs. Eukaryotic cells

K ing do m M o ne ra d ivid e d in to th re e m a jo r g ro up s o r S ub k in g do m s

E u b ac te ria A rch ae b ac te ria C ya no b ac te ria

K in gd o m M on e ra

Bacterial cell size, shapes and arrangements

• 2.0 – 10.0 uM in length

• Eukaryotic cells ~10x larger

• 3 common morphologies– bacillus = rod-shaped

– coccus = spherical shaped

– spirillum = spiral shaped

• Many arrangements– diplo-

– strepto-

– Staphylo-

***spirochetes**

Bacterial morphologies

• Morphology can be used as an initial identifier

• However, shape can change in some bacteria depending on environs– “pleomorphic” cells

Bacterial ultrastructure

1) Cell wall structure

• Alternating NAM & NAG amine sugars produce layers of block units– NAM = n-acetylmuramic acid

– NAG = n-acetylglucosamine

• Layers connected by tetrapeptide chains linked to NAM’s

• Penta-glycine interbridges connect tetrapeptides in Gram + cells (sensitive to penicillin)

• Direct peptide bonds connect tetrapeptides in Gram – cells (not sensitive to penicillin)

Make up peptidoglycan

Alternating NAM-NAG with tetrapeptide connections

Gram positive cell wall structure

Ok, not too bad – now for something completely different – Gram negative cell walls!

Gram negative cell wall structure

Gram neg. cell walls are composed of peptidoglycan AND an outer membrane; it is multi-layered!!

Gram negative LPS*

• *Lipopolysaccharide contains 3 parts:– Antigen O – can change shape in dif’t environs

– Core polysaccharide – contains neg. charge

– Lipid A – also called ‘endotoxin A’; released upon cell death and can have toxic affect on nearby cell membranes

Gram pos. vs Gram neg cell walls

• Thick peptidoglycan– 20-80 nm thick

• Retains CV-I complex of Gram stain

• Teichoic acid anchors cell wall to cell membrane and imparts a negative charge– Glycerol-P polymer

• Two part structure– Thin peptidoglycan

(10-20 nm)

– Outer membrane

• Outer membrane contains LPS

• LPS imparts a negative charge

Gram + Gram -

The Gram stain

2) Bacterial flagella

• Composed of: 1) basal body, 2) filament, 3) hook• Basal body connects to cell wall and to cell membrane• Uses ATP to spin

Arrangements of flagella

Bacteria are hampered to some extent by flagellar rotation