The Building blocks of a
bacterial cell
by
E. Börje Lindström
This learning object has been funded by the European Commissions FP6 BioMinE project
Cell types
• prokaryotes:
- bacteria
- archeons
• eukaryotes:
- yeast
- algae
- fungi
- plant
- animal
Bacteria
General aspects
• Bacteria exist in many different forms and sizes.
• Forms:
- spherical
e.g. Staphylococcus aureus
-curved
Spirilles and spirochetes
or helical
- rod shaped
• Sizes:
e.g. Escherichia coli
1 mm
1- 2 mm
Depending on growth media!
General aspects, cont.
• Weight (dry):
• Volume:
• Aggregates:
~ 10-13 – 10-12 g
~ 10-12 ml
- Especially among cocci
- diplococci
- streptococci
- staphylococci
- tetrads
The Bacterial Cell - Schematic
Cell wall
Cytoplasm
membrane
Cytoplasm
Cytoplasm
• In the cytoplasm most of the biosynthesis of the cell occur.
It is a suspension of:
• small soluble molecules
• macro molecules
• particles
-buildingblocks for macromolecules e.g.
aa, metal salts etc.
- protein/enzymes, RNA etc.
- ribosomes, granula etc.
Cytoplasm, cont.
The ’nucleus’ - a comparison
Prokaryots
Eykaryotes
Membrane
-
+
Endoplasmic
reticulum
-
+
1
>1
Cromosome(s)
closed
DNA
(1 molecule)
open
DNA + proteins
(histones)
• Slow growth – 1-2 copies of the chromosome
• Rapid growth – 2-5 copies
Cytoplasm, cont.
- nucleoproteins = rRNA + proteins
Ribosomes
- function in protein synthesis
• Prokaryotes
• Eukaryotes
• 2 subunits
16S rRNA +
21 diff. prot
18S rRNA +
30S
40S
50S
60S
23S rRNA +
34 diff. prot
?? diff. prot
28S rRNA +
?? diff. prot
70S
80S
Cytoplasm membrane
Function:
- selective permeability barrier
- transport mechanisms
- electron transport chain
Properties:
-unit membrane of phospholipids
- ~8 nm thick
- hydrofilic (glycerol) outer part
- hydrophobic (fatty acids) inner part
- protein inbedded (transport)
- a ’floating’ structure, stabilized with Mg2+ and
Ca2+
Cell Wall
• Constitute ~ 10-20% of the dry weight of the baterium
• almost all prokaryotes have a cell wall
Funktion:
- a mechanical protection
- gives the cell its form
Strength:
- due to special chemical structures in all
types of cells
• cellulose – plants
• chitin – fungi
• mucopeptides (murein) - eubacteria
Cell Wall, cont.
The murein structure
• a net work around the cell
• carbohydrates
• peptides
Cell Wall, cont.
Chain of carbohydrates:
-alternating amin suger
- NAG, N-acetyl glucoseamin
- NAM, N-acetyl muramic acid
NAM – NAG – NAM – NAG – NAM – NAG
L-ala
Peptide bond
D-glu
L-lys
D-ala
D-ala
(D-ala)
(aa)n
D-ala
L-lys
aa with two amino groups
(alternative DAP)
D-glu
L-ala
NAM – NAG – NAM – NAG – NAM – NAG
Gram staining
Heat fixation of the
cells (on a object glass)
+ crystal violet (blue dye) +
I2-KI
All cells blue
+ aceton/alcohol
Blue cells
Destained cells,
grayish
+ safranin (red dye)
G+, blue/violett cells
G-, red cells
Components of the cell wall
• Summary:
Component
Gram +
Gram -
 15-18 nm
 10 nm
Teichoic acid (PO4-rich)
+
-
Lipoprotein
-
+
Lipopolysccharide (LPS)
-
+
(+)
(+)
Murein, mucopeptide
Proteins
Lysozyme treatment
NAM – NAG – NAM – NAG – NAM – NAG
lysozyme
G+:
G-:
- protoplast formation,
cell wall completely
removed
- spheroplast formation,
part of the cell wall left
Granula
• Storage
of energy and carbon sources
- Glykogen
- Starch
- b-hydroxybutyrate
• Others
-Polyphosphates
- elementar sulphur
Cell surface structures
• Pili/ fimbriae:
- only in G -
-short protein tube
- Ø ~ 7 nm
- helical structure
- several types e.g. F-pili
- Function
• Flagella:
- involved in adherence to
surfaces
-motility organ
- thin (~ 20 nm) long protein molecules
- polar or peritrichious
Bacterial spores
• A heat resistant form of the cell (endospore)
1 cell
1 spore
1 cell
• Found only in Bacillus (aerob) and
Clostridium (anaerob)
Capsules and slime layers
• Usually a polysaccharide or protein layer
excreted from the cell
Function:
-attachement to surfaces
- protection against phagocytosis