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 e.g. Escherichia coli

• Sizes: 1 m

1- 2 m

Depending on growth media!

General aspects, cont.

• Weight (dry):~ 10-13 – 10-12 g

• Volume: ~ 10-12 ml

• Aggregates: - 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 -buildingblocks for macromolecules e.g. aa, metal salts etc.

• macro molecules - protein/enzymes, RNA etc.

• particles - ribosomes, granula etc.

Prokaryots Eykaryotes

Membrane - +

Endoplasmic reticulum -

Cromosome(s)

+

1 >1

closed open

DNA

(1 molecule)

DNA + proteins (histones)

Cytoplasm, cont.The ’nucleus’ - a comparison

• Slow growth – 1-2 copies of the chromosome

• Rapid growth – 2-5 copies

Cytoplasm, cont.Ribosomes - nucleoproteins = rRNA + proteins

- function in protein synthesis

• Prokaryotes • Eukaryotes

• 2 subunits

30S

50S

40S

60S

16S rRNA +

21 diff. prot

23S rRNA +

34 diff. prot

18S rRNA +

?? diff. prot

28S rRNA +

?? diff. prot

70S 80S

Cytoplasm membraneFunction: - 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

D-glu

L-lys

D-ala

D-ala

NAM – NAG – NAM – NAG – NAM – NAG

(D-ala)

D-ala

L-lys

D-glu

L-ala

(aa)n

Peptide bond

aa with two amino groups

(alternative DAP)

Gram stainingHeat 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

Component Gram + Gram -

Murein, mucopeptide 15-18 nm 10 nm

Teichoic acid (PO4-rich) + -

Lipoprotein - +

Lipopolysccharide (LPS) - +

Proteins (+) (+)

• Summary:

Lysozyme treatment

NAM – NAG – NAM – NAG – NAM – NAG

lysozyme

G+: - protoplast formation, cell wall completely removed

G-: - spheroplast formation, part of the cell wall left

Granula• Storage of energy and carbon sources

- Glykogen

- Starch

- -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 - involved in adherence to surfaces

• Flagella: -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