Microbiology Lecture 2 - Chapter 3-4

Queens college Summer session

Peptidoglycan Structure

Responsible for linking the cell wall together

• made up of N-Acetylglucosamine (NAG) and N-acetylmuramic acid (NAM)

• provides rigidity and flexibility

• susceptible to osmotic pressure causing lysis.

Gram Positive Cell Wall

contains

• thick peptidoglycan wall with anchors or teichoic acid (neg charge)

• periplasmic space

• bi-phospholipid layer thats porous

• 

Gram Negative Cell Wall

1. outer layer composed of Lipopolysaccharide (LPS) includes porins

2. bi-phospholipid layer under the LPS, contains Lipid A, porins and lipoprotein

3. Small layer of peptidoglycans

4. inner cell wall comprised of phospholipids with embedded integral membrane proteins

Lipid A

potent endotoxin

may cause septic shock

endotoxin

are the lipopolysaccharide-protein complexes, produced at the time of cell death

only released when the cell undergoes lysis

Exotoxin

are polypeptide proteins excreted by few species of bacteria

Gram Negative Infection

entire immune system is notified of a pathogen and reacts as a whole

could potentially cause high blood pressure and convulsion

Porin

water filled channel allows passage of molecules smaller than 600 dallons

Lipopolysaccharide (LPS)

Makes a permeability barrier

• restrict of bile, antibiotics, etc

• protects pathogenic bacteria from hoes defenses by changing O-antigen

Glycocalyx

External coating (mucus) of microbes

includes slime layer and capsule (kinda like a biofilm)

allows adherence to surfaces, protects and hydrates the cell

can tell if capsule by negative staining

two types of glycocalyx

1. slime layer: twitching motility

2. capsule: K-antigen

S layers

Structured layers of protein or glycoprotein, self-assemble to protect from environmental stress, involved in cell wall synthesis and maintenance.

• akin to armor that protects from pH fluctuations, osmotic stress, enzymes and predation

• involved in cell division

the S layer in Gram neg bacteria

the s layer adheres to the outer membrane (similarity: the outermost layer)

the S layer in gram positive bacteria

the s layer is associated with the peptidoglycan (similarity: the outermost layer)

Fimbriae

Hairlike bristles for attachment, numerous on the body, adhere to surfaces or other microbes.

Pili

Protein tubes for anchoring microbes, involved in reproduction, less numerous than fimbriae.

Flagella

Threadlike appendages for mobility and attachment, different arrangements and amounts, involved in chemotaxis and motility.

Ribosomes

Involved in protein synthesis, targeted by antibiotics, have different settling rates for targeting.

Nucleoid and Plasmids

Genetic material organization, nucleoid contains chromosomal DNA, plasmids carry additional genes, used for transformation.

Endospores

Survival structures with coat, cortex, and core layers, dehydrated for stability, dormant state until conditions are favorable.

Archaeal Membranes

Composed of unique lipids, have a monolayer, stable in extreme environments, lack peptidoglycan but have similar structural integrity.

Peptidoglycan

is the structure that is responsible for linking the cell wall together

Anchors

bio name called teichoic acid that are negative charge

they anchor together the various layers of cell wall and keeps the cell enveloped

acts as the repellent

Periplasmic space

open to the outside (outside the periplasmic space)

enzymes will stay in this area on standby