3. Bacterial Cell Walls

The cell wall confers ___ and ___ to the cell.

Shape and rigidity

What is the sacculus?

The continuous, bag-shaped peptidoglycan cell wall that entirely encases a bacterium

What is the main function of the cell wall?

Protecting the (any) cell membrane

Peptidoglycan

A disaccharide unit of glycine has an attached peptide of four to six amino acids

The combination of peptidoglycan are…

NAM and NAG

Peptidoglycan is unique to…?

Bacteria; thus, the enzymes responsible for its biosynthesis make excellent targets for antibiotics

Penicillin targets what enzyme and what is the function of the enzyme?

Transpeptidiase; the enzyme that cross links the amino acids in peptidoglycan

Describe Gram-Positive Bacteria

• stains more purple

• Has a thick peptidoglycan layer

• Threaded by teichoic acids

What charge do teichoic acids have?

Negative

Describe Gram-Negative Bacteria

• stains more pink/red

• Thin layer of peptidoglycan

• Have an outer membrane

  • This makes it more resistant to penicillin

What is unique to gram-negative bacteria?

LPS= lipopolysaccharides

What are lipopolysaccharides (LPS)? Where are they located?

• in the outer membrane

• Provides support to the cell; if destroyed, the whole cell falls apart

• Negatively charged threads

• In humans can sometimes act as an endotoxin

What are endotoxins?

Substances that when released from dead bacteria…

• overstimulates human immune cells

• Dysregulated human cells signaling (cytokines storm)

Hypotonic Environments

• solute concentration outside cell is less than inside cell

• Water moves into cell and cell swells

• Cell wall protects from lysis (the bursting of a cell when too much water enters it)

Hypertonic Environements

• solute concentration outside cell is greater than inside cell

• Water leaves cell and cytoplasm shrivels up

• Cell wall protects from plasmolysis (the shrinking of a plant cell’s cytoplasm and plasma membrane away from its rigid cell wall caused by water loss)

Extracellular Vesicles

small membrane bound particles

How do extracellular vesicles develop?

Develop when a membrane buds out, pinches off, and is released from the cell

Gram-Positive EVs

Made of the plasma membrane surround a small amount of cytoplasm

Gram-Negative EVs

Made up of LPS, contains organic matter surround a sample of periplasm

Which components are found outside the cell wall? (In the outermost layer in the cell envelope)

• capsules

• Slime layers

• S-layers

Capsules

Well organized layers made of polysaccharides that are covalently bonded and difficult to wash away

What are the protective advantages of capsules?

• resistant to host immune cells

• Protect from desiccation

• Exclude viruses and detergents

Slime layers

Polysaccharide layers that are unorganized and easily washed away

S-Layers

Geometric pattern made of protein that aid in protecting from ion and pH fluctuations

What are the functions of the S-Layers ?

To the outer membrane

In gram-neg bacteria, the s-layer adheres to where?

To the outer membrane

In gram-pos bacteria, the s-layer is associated with what layer?

The peptidoglycan