gram-negative cell envelope

what makes up a prokaryotic cell

the cytoplasm is a crowded, gel-like space and the plasma membrane surrounds it

outside that is a cell wall and in gram-negative bacteria there is also an outer membrane

what is the gram-negative cell envelope made of

three main layers: an inner layer, thin peptidoglycan cell wall, and outer membrane that contains LPS

what is LPS

a large glycolipid found in the outer membrane of gram-negative bacteria. helps protect the cell and acts as a barrier to antibiotics

what are the three parts of the LPS

Lipid A, the core region, and the O-antigen

what is lipid A

the toxic portion of the LPS. anchors LPS into the membrane and is responsible for endotoxin activity

what is endotoxin

lipid A of LPS. can trigger strong immune responses in humans

what pathway makes lipid A

the raetz pathway

where are different parts of LPS made

core sugars are made in the cytoplasm

o-antigen is built in the periplasm

how is the LPS fully assembled

lipid A is made first, then core sugars are added, and finally the O-antigen is attached

how does LPS get to the outer membrane

it is transported by a system of proteins called LptA-G

what is the PEZ model

LPS molecules are pushed one after another through a protein bridge, like candy in a PEZ dispenser.

What protein flips LPS across the inner membrane?

What protein flips LPS across the inner membrane?

Why is LPS essential for bacteria?

It stabilizes the outer membrane and protects against harmful substances.

What happens if LPS synthesis is disrupted?

The membrane becomes unstable. Bacteria become more sensitive to antibiotics or may die.

How does LPS affect humans?

It triggers a strong immune response.

What can high levels of LPS cause?

Fever, low blood pressure, inflammation, and septic shock.

What is sepsis?

A dangerous condition with high fever, fast heart rate, low blood pressure, and organ dysfunction.

How does the body detect LPS?

Through Toll-like receptors, especially TLR4.

What happens after TLR4 detects LPS?

It activates signaling pathways that increase cytokine production and inflammation.

Why is this response dangerous?

Too much cytokine release can lead to septic shock.

What is innate immunity?

The body’s first line of defense against pathogens.

Two major functions of innate immunity?

Destroys pathogens and sends signals through cytokines.

What is phagocytosis?

Immune cells like macrophages engulf and destroy bacteria.

What is opsonization?

When antibodies coat a pathogen to make it easier to be engulfed.

What do antigen-presenting cells (APCs) do?

display pieces of pathogens on their surface to activate T cells.

Which cells act as APCs?

Macrophages, dendritic cells, and B cells.

What is the basic structure of an antibody?

Fab regions that bind antigen and an Fc region that interacts with immune cells.

Why is antibody orientation important?

Determines how effectively immune cells recognize and respond to pathogens

What are the two main colony types?

smooth and rough

What determines smooth vs rough colonies?

The structure of LPS, especially the O-antigen.

What is the O-antigen?

A repeating sugar chain extending outward from LPS.

What controls O-antigen length?

The Wzz system

Why does O-antigen length matter?

Affects virulence and how bacteria interact with the immune system.

Can LPS affect other bacterial systems

Yes. It can influence systems like the Type III secretion system.

Why is LPS a good antibiotic target?

It is essential and unique to bacteria.

How do some new antibiotics work against LPS?

Block LPS transport by trapping it in the transporter system.

Why are Gram-negative bacteria hard to kill?

Outer membrane with LPS blocks many antibiotics.

How is LPS formed?

Lipid A is synthesized first, then core sugars are added in the cytoplasm, and finally O-antigen is attached in the periplasm before transport to the outer membrane.

What is endotoxin?

The Lipid A portion of LPS that triggers immune responses.

Can LPS interfere with other systems?

Yes, it can affect processes like secretion systems and virulence.

Does LPS affect colony morphology?

Yes. It determines smooth vs rough colony types.