Cell Walls and Bacterial Classification

These flashcards cover key concepts regarding the structure and function of bacterial cell walls, including distinctions between gram-positive and gram-negative bacteria.

What is the major component of bacterial cell walls?

Peptidoglycan.

What two monosaccharides make up peptidoglycan?

N-acetylmuramic acid (NAM) and N-acetylglucosamine (NAG).

What structure does the tetrapeptide form in peptidoglycan?

A crosslinking bridge that helps create a lattice-like structure.

What is mycoplasma?

The only bacteria that does not have a cell wall.

What role does the cell wall play in bacteria?

It helps maintain the shape of the bacteria and offers protection against environmental changes.

What distinguishes gram-positive bacteria?

They have a thick cell wall containing teichoic acids.

What color do gram-positive bacteria stain?

Purple.

What is the outer membrane in gram-negative bacteria composed of?

A lipid bilayer that serves as a barrier.

What is the significance of lipopolysaccharides (LPS)?

They are found only in gram-negative bacteria and can trigger severe immune responses. Toxin

What is the function of lysozyme?

It breaks down the NAM and NAG backbone of peptidoglycan, primarily affecting gram-positive bacteria.

What action does penicillin have on bacterial cell walls?

It prevents crosslinking in peptidoglycan, effectively targeting gram-positive bacteria.

Function of cell walls

Shape, resists osmotic pressure, protects membrane and interior region, Anchorage for flagella

Clinical cell wall

Contributes to ability to cause disease

Site of action for some antibiotics

Used to differentiate bacteria

Explain gram + cell walls

Thick cell wall. Sits outside of the plasma membrane

Many layers of peptidoglycan

Teichoic acid - Alcohol + phosphate

Function of gram + cell wall

Regulates cation into and out of the cell

Regulates autolysins that degrade cell wall

Antigenic specificity for ID

Anchors cell wall to plasma membrane

What color does gram + stain?

purple

Explain mycolic acid

Mycolic acid is in mycobacterium - it is an acid - it stains pink/red or gram negative. Thick waxy lipid layer

Mycolic acid stain?

Acid fast. Cell must be heated thoroughly to penetrate the waxy lipid bilayer

Gram - cell wall

Has a thin outer membrane + cell wall

True phospholipid bilayer

Permeable to small molecules

Porins present - these are channels for small anionic compounds

Not very permeable to antibiotics because it is not lipid soluble

Lipopolysaccharide layer

Thin layer of peptidoglycan

Why are gram - cells so dangerous?

Heat stable, can’t be autoclaved. Weakly immunogenic, toxic in high doses, Capable of producing fever, blood clots, weakness, shock, etc.

Why are antibiotics general not used in large doses for gram - cells?

Lipopolysaccharides are incredibly toxic to the human body, so when these cells are broken down and this toxin is released it causes major harm

Lysozyme

Enzyme that breaks down NAM + NAG that is exposed

Works great for gram + as NAM and NAG is exposed in these cells

Penicilin

Disrupts the cross bridge connection between cells. Works great if found early enough in development. If fully developed it won’t work on these cells.

NAM and NAG cross-bridge

structure that provides rigidity and strength to bacterial cell walls, essential for maintaining cell integrity.