Chapter 4: prokaryotic cell

Prokaryotes:

•One circular chromosome, not in a membrane

•No histones

•No organelles

•Bacteria: peptidoglycan cell walls

•Archaea: pseudomurein cell walls

•Divides by binary fission

Eukaryote:

•Paired chromosomes, in the nuclear membrane

•Histones

•Organelles

•Polysaccharide cell walls, when present

Divides by mitosis

The cell wall in prokaryotes…

•Prevents osmotic lysis (10-25 atmospheres of internal pressure)

•Determines shape (genetic characteristic)

•Made of peptidoglycan (in bacteria)

Peptidoglycan…

•Polymer of disaccharide
N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM)

•Cross-linked by short chain of aa (peptide)

•Forms dynamic, mesh-like girdle around cell

Gram Positive Cell walls have…

•Thick peptidoglycan

•Teichoic acids

•In acid-fast cells, contains mycolic acids (= waxy substance)

Gram Negative Cell walls have…

•Thin peptidoglycan

  (as mono-layer)

•No teichoic acids

•Outer membrane

  ( LPS layer)

Gram-Positive Cell Walls contain…

•Teichoic acids – cell wall anchor

• Lipoteichoic acid links to plasma membrane

• Wall teichoic acid links to peptidoglycan

•May regulate movement of cations.

•Polysaccharides provide antigenic variation.

Gram-Negative outer membranes contain…

• •Lipopolysaccharides, lipoproteins, phospholipids      (= “LPS”) 

• •Lipid A  (endotoxin)

• •Porins (proteins) form channels through membrane (entry for molecules)

  • Limits size of molecules entering cell

Gram-positive Gram Stain Mechanism

•Alcohol dehydrates thick peptidoglycan

•CV-I2 crystals cannot leave

Gram-negative Gram Stain Mechanism

•Alcohol dissolves outer membrane and leaves holes in peptidoglycan.

•CV-I2 washes out

Mycoplasmas have..

atypical cell walls.

•Lack cell walls (genetic)

•Sterols in plasma membrane
 provide stability

Archaea have…

atypical cell walls.

•Wall-less or

•Walls of pseudomurein
(lack NAM and D amino acids)

Flagella provide 

mobility 

Pilli provide 

attachment. 

The flagella is made out of: 

•Filament made of chains of flagellin

  (protein subunits)

•Attached to a protein hook

•Anchored to the wall and membrane by the basal body

Gram negative flagella move in a

propeller motion

Different ways bacteria move to favorable conditions:

•Chemotaxis

• sense chemicals

•Phototaxis

• sense light intensity

•Aerotaxis

• favorable oxygen concentrations

•Magnetotaxis

• move along magnetic lines

How bacteria move:

• Sensing: Bacteria have receptor proteins that detect stimuli in the environment.

• Signal Processing: The signal alters the rotation of the flagella.

• Movement Response:

  • Run: Smooth, straight swimming toward attractant

  • Tumble: Random movement or change in direction away from repellent

Axial Filaments are… 

•In spirochetes

•Anchored at one end
of a cell

•Rotation causes cell
to move

glycocalyx definition

the outermost slimy, gummy, layer found outside the cell wall of many bacteria.

function of glycocalyx

•Protection Against drying out

•Against phagocytosis

•Adherence to surface (biofilm)

Cytoplasmic membrane function

•regulates passage into and out of cell (= transport)

• made of phospholipid bilayer and proteins

Nucleoid

no histone proteins, contains genetic materiel

Ribosomes

protein synthesis 

inclusion bodies (prokayrotes)

functions as internal storage for energy.

cytoplasm

gel like, 85%> water. site of metabolic activity.

sporulation formation steps:

1. Copy DNA

2. Separate DNA into spore area (forespore)

3. Wrap forespore with layers (cortex + coat)

4. Harden and mature

5. Spore released (mother cell breaks open)